Celestin Apprentice 7/Apprentice-Release7.iso/Source Code/C/Applications/Tcl-Tk 8.0/Pre-installed version/tk8.0/generic/tkTextDisp.c

C/C++ Source or Header | 1997-08-15 | 148.6 KB | 5,016 lines | [TEXT/CWIE]

/*
 * tkTextDisp.c --
 *
 *    This module provides facilities to display text widgets.  It is
 *    the only place where information is kept about the screen layout
 *    of text widgets.
 *
 * Copyright (c) 1992-1994 The Regents of the University of California.
 * Copyright (c) 1994-1997 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * SCCS: @(#) tkTextDisp.c 1.124 97/07/11 18:01:03
 */

#include "tkPort.h"
#include "tkInt.h"
#include "tkText.h"

/*
 * The following structure describes how to display a range of characters.
 * The information is generated by scanning all of the tags associated
 * with the characters and combining that with default information for
 * the overall widget.  These structures form the hash keys for
 * dInfoPtr->styleTable.
 */

typedef struct StyleValues {
    Tk_3DBorder border;        /* Used for drawing background under text.
                 * NULL means use widget background. */
    int borderWidth;        /* Width of 3-D border for background. */
    int relief;            /* 3-D relief for background. */
    Pixmap bgStipple;        /* Stipple bitmap for background.  None
                 * means draw solid. */
    XColor *fgColor;        /* Foreground color for text. */
    Tk_Font tkfont;        /* Font for displaying text. */
    Pixmap fgStipple;        /* Stipple bitmap for text and other
                 * foreground stuff.   None means draw
                 * solid.*/
    int justify;        /* Justification style for text. */
    int lMargin1;        /* Left margin, in pixels, for first display
                 * line of each text line. */
    int lMargin2;        /* Left margin, in pixels, for second and
                 * later display lines of each text line. */
    int offset;            /* Offset in pixels of baseline, relative to
                 * baseline of line. */
    int overstrike;        /* Non-zero means draw overstrike through
                 * text. */
    int rMargin;        /* Right margin, in pixels. */
    int spacing1;        /* Spacing above first dline in text line. */
    int spacing2;        /* Spacing between lines of dline. */
    int spacing3;        /* Spacing below last dline in text line. */
    TkTextTabArray *tabArrayPtr;/* Locations and types of tab stops (may
                 * be NULL). */
    int underline;        /* Non-zero means draw underline underneath
                 * text. */
    Tk_Uid wrapMode;        /* How to handle wrap-around for this tag.
                 * One of tkTextCharUid, tkTextNoneUid,
                 * or tkTextWordUid. */
} StyleValues;

/*
 * The following structure extends the StyleValues structure above with
 * graphics contexts used to actually draw the characters.  The entries
 * in dInfoPtr->styleTable point to structures of this type.
 */

typedef struct TextStyle {
    int refCount;        /* Number of times this structure is
                 * referenced in Chunks. */
    GC bgGC;            /* Graphics context for background.  None
                 * means use widget background. */
    GC fgGC;            /* Graphics context for foreground. */
    StyleValues *sValuePtr;    /* Raw information from which GCs were
                 * derived. */
    Tcl_HashEntry *hPtr;    /* Pointer to entry in styleTable.  Used
                 * to delete entry. */
} TextStyle;

/*
 * The following macro determines whether two styles have the same
 * background so that, for example, no beveled border should be drawn
 * between them.
 */

#define SAME_BACKGROUND(s1, s2) \
    (((s1)->sValuePtr->border == (s2)->sValuePtr->border) \
        && ((s1)->sValuePtr->borderWidth == (s2)->sValuePtr->borderWidth) \
        && ((s1)->sValuePtr->relief == (s2)->sValuePtr->relief) \
        && ((s1)->sValuePtr->bgStipple == (s2)->sValuePtr->bgStipple))

/*
 * The following structure describes one line of the display, which may
 * be either part or all of one line of the text.
 */

typedef struct DLine {
    TkTextIndex index;        /* Identifies first character in text
                 * that is displayed on this line. */
    int count;            /* Number of characters accounted for by this
                 * display line, including a trailing space
                 * or newline that isn't actually displayed. */
    int y;            /* Y-position at which line is supposed to
                 * be drawn (topmost pixel of rectangular
                 * area occupied by line). */
    int oldY;            /* Y-position at which line currently
                 * appears on display.  -1 means line isn't
                 * currently visible on display and must be
                 * redrawn.  This is used to move lines by
                 * scrolling rather than re-drawing. */
    int height;            /* Height of line, in pixels. */
    int baseline;        /* Offset of text baseline from y, in
                 * pixels. */
    int spaceAbove;        /* How much extra space was added to the
                 * top of the line because of spacing
                 * options.  This is included in height
                 * and baseline. */
    int spaceBelow;        /* How much extra space was added to the
                 * bottom of the line because of spacing
                 * options.  This is included in height. */
    int length;            /* Total length of line, in pixels. */
    TkTextDispChunk *chunkPtr;    /* Pointer to first chunk in list of all
                 * of those that are displayed on this
                 * line of the screen. */
    struct DLine *nextPtr;    /* Next in list of all display lines for
                 * this window.   The list is sorted in
                 * order from top to bottom.  Note:  the
                 * next DLine doesn't always correspond
                 * to the next line of text:  (a) can have
                 * multiple DLines for one text line, and
                 * (b) can have gaps where DLine's have been
                 * deleted because they're out of date. */
    int flags;            /* Various flag bits:  see below for values. */
} DLine;

/*
 * Flag bits for DLine structures:
 *
 * HAS_3D_BORDER -        Non-zero means that at least one of the
 *                chunks in this line has a 3D border, so
 *                it potentially interacts with 3D borders
 *                in neighboring lines (see
 *                DisplayLineBackground).
 * NEW_LAYOUT -            Non-zero means that the line has been
 *                re-layed out since the last time the
 *                display was updated.
 * TOP_LINE -            Non-zero means that this was the top line
 *                in the window the last time that the window
 *                was laid out.  This is important because
 *                a line may be displayed differently if its
 *                at the top or bottom than if it's in the
 *                middle (e.g. beveled edges aren't displayed
 *                for middle lines if the adjacent line has
 *                a similar background).
 * BOTTOM_LINE -        Non-zero means that this was the bottom line
 *                in the window the last time that the window
 *                was laid out.
 */

#define HAS_3D_BORDER    1
#define NEW_LAYOUT    2
#define TOP_LINE    4
#define BOTTOM_LINE    8

/*
 * Overall display information for a text widget:
 */

typedef struct TextDInfo {
    Tcl_HashTable styleTable;    /* Hash table that maps from StyleValues
                 * to TextStyles for this widget. */
    DLine *dLinePtr;        /* First in list of all display lines for
                 * this widget, in order from top to bottom. */
    GC copyGC;            /* Graphics context for copying from off-
                 * screen pixmaps onto screen. */
    GC scrollGC;        /* Graphics context for copying from one place
                 * in the window to another (scrolling):
                 * differs from copyGC in that we need to get
                 * GraphicsExpose events. */
    int x;            /* First x-coordinate that may be used for
                 * actually displaying line information.
                 * Leaves space for border, etc. */
    int y;            /* First y-coordinate that may be used for
                 * actually displaying line information.
                 * Leaves space for border, etc. */
    int maxX;            /* First x-coordinate to right of available
                 * space for displaying lines. */
    int maxY;            /* First y-coordinate below available
                 * space for displaying lines. */
    int topOfEof;        /* Top-most pixel (lowest y-value) that has
                 * been drawn in the appropriate fashion for
                 * the portion of the window after the last
                 * line of the text.  This field is used to
                 * figure out when to redraw part or all of
                 * the eof field. */

    /*
     * Information used for scrolling:
     */

    int newCharOffset;        /* Desired x scroll position, measured as the
                 * number of average-size characters off-screen
                 * to the left for a line with no left
                 * margin. */
    int curPixelOffset;        /* Actual x scroll position, measured as the
                 * number of pixels off-screen to the left. */
    int maxLength;        /* Length in pixels of longest line that's
                 * visible in window (length may exceed window
                 * size).  If there's no wrapping, this will
                 * be zero. */
    double xScrollFirst, xScrollLast;
                /* Most recent values reported to horizontal
                 * scrollbar;  used to eliminate unnecessary
                 * reports. */
    double yScrollFirst, yScrollLast;
                /* Most recent values reported to vertical
                 * scrollbar;  used to eliminate unnecessary
                 * reports. */

    /*
     * The following information is used to implement scanning:
     */

    int scanMarkChar;        /* Character that was at the left edge of
                 * the window when the scan started. */
    int scanMarkX;        /* X-position of mouse at time scan started. */
    int scanTotalScroll;    /* Total scrolling (in screen lines) that has
                 * occurred since scanMarkY was set. */
    int scanMarkY;        /* Y-position of mouse at time scan started. */

    /*
     * Miscellaneous information:
     */

    int dLinesInvalidated;    /* This value is set to 1 whenever something
                 * happens that invalidates information in
                 * DLine structures;  if a redisplay
                 * is in progress, it will see this and
                 * abort the redisplay.  This is needed
                 * because, for example, an embedded window
                 * could change its size when it is first
                 * displayed, invalidating the DLine that
                 * is currently being displayed.  If redisplay
                 * continues, it will use freed memory and
                 * could dump core. */
    int flags;            /* Various flag values:  see below for
                 * definitions. */
} TextDInfo;

/*
 * In TkTextDispChunk structures for character segments, the clientData
 * field points to one of the following structures:
 */

typedef struct CharInfo {
    int numChars;        /* Number of characters to display. */
    char chars[4];        /* Characters to display.  Actual size
                 * will be numChars, not 4.  THIS MUST BE
                 * THE LAST FIELD IN THE STRUCTURE. */
} CharInfo;

/*
 * Flag values for TextDInfo structures:
 *
 * DINFO_OUT_OF_DATE:        Non-zero means that the DLine structures
 *                for this window are partially or completely
 *                out of date and need to be recomputed.
 * REDRAW_PENDING:        Means that a when-idle handler has been
 *                scheduled to update the display.
 * REDRAW_BORDERS:        Means window border or pad area has
 *                potentially been damaged and must be redrawn.
 * REPICK_NEEDED:        1 means that the widget has been modified
 *                in a way that could change the current
 *                character (a different character might be
 *                under the mouse cursor now).  Need to
 *                recompute the current character before
 *                the next redisplay.
 */

#define DINFO_OUT_OF_DATE    1
#define REDRAW_PENDING        2
#define REDRAW_BORDERS        4
#define REPICK_NEEDED        8

/*
 * The following counters keep statistics about redisplay that can be
 * checked to see how clever this code is at reducing redisplays.
 */

static int numRedisplays;    /* Number of calls to DisplayText. */
static int linesRedrawn;    /* Number of calls to DisplayDLine. */
static int numCopies;        /* Number of calls to XCopyArea to copy part
                 * of the screen. */

/*
 * Forward declarations for procedures defined later in this file:
 */

static void        AdjustForTab _ANSI_ARGS_((TkText *textPtr,
                TkTextTabArray *tabArrayPtr, int index,
                TkTextDispChunk *chunkPtr));
static void        CharBboxProc _ANSI_ARGS_((TkTextDispChunk *chunkPtr,
                int index, int y, int lineHeight, int baseline,
                int *xPtr, int *yPtr, int *widthPtr,
                int *heightPtr));
static void        CharDisplayProc _ANSI_ARGS_((TkTextDispChunk *chunkPtr,
                int x, int y, int height, int baseline,
                Display *display, Drawable dst, int screenY));
static int        CharMeasureProc _ANSI_ARGS_((TkTextDispChunk *chunkPtr,
                int x));
static void        CharUndisplayProc _ANSI_ARGS_((TkText *textPtr,
                TkTextDispChunk *chunkPtr));
static void        DisplayDLine _ANSI_ARGS_((TkText *textPtr,
                DLine *dlPtr, DLine *prevPtr, Pixmap pixmap));
static void        DisplayLineBackground _ANSI_ARGS_((TkText *textPtr,
                DLine *dlPtr, DLine *prevPtr, Pixmap pixmap));
static void        DisplayText _ANSI_ARGS_((ClientData clientData));
static DLine *        FindDLine _ANSI_ARGS_((DLine *dlPtr,
                TkTextIndex *indexPtr));
static void        FreeDLines _ANSI_ARGS_((TkText *textPtr,
                DLine *firstPtr, DLine *lastPtr, int unlink));
static void        FreeStyle _ANSI_ARGS_((TkText *textPtr,
                TextStyle *stylePtr));
static TextStyle *    GetStyle _ANSI_ARGS_((TkText *textPtr,
                TkTextIndex *indexPtr));
static void        GetXView _ANSI_ARGS_((Tcl_Interp *interp,
                TkText *textPtr, int report));
static void        GetYView _ANSI_ARGS_((Tcl_Interp *interp,
                TkText *textPtr, int report));
static DLine *        LayoutDLine _ANSI_ARGS_((TkText *textPtr,
                TkTextIndex *indexPtr));
static int        MeasureChars _ANSI_ARGS_((Tk_Font tkfont,
                CONST char *source, int maxChars, int startX,
                int maxX, int tabOrigin, int *nextXPtr));
static void        MeasureUp _ANSI_ARGS_((TkText *textPtr,
                TkTextIndex *srcPtr, int distance,
                TkTextIndex *dstPtr));
static int        NextTabStop _ANSI_ARGS_((Tk_Font tkfont, int x,
                int tabOrigin));
static void        UpdateDisplayInfo _ANSI_ARGS_((TkText *textPtr));
static void        ScrollByLines _ANSI_ARGS_((TkText *textPtr,
                int offset));
static int        SizeOfTab _ANSI_ARGS_((TkText *textPtr,
                TkTextTabArray *tabArrayPtr, int index, int x,
                int maxX));
static void        TextInvalidateRegion _ANSI_ARGS_((TkText *textPtr,
                TkRegion region));


/*
 *----------------------------------------------------------------------
 *
 * TkTextCreateDInfo --
 *
 *    This procedure is called when a new text widget is created.
 *    Its job is to set up display-related information for the widget.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    A TextDInfo data structure is allocated and initialized and attached
 *    to textPtr.
 *
 *----------------------------------------------------------------------
 */

void
TkTextCreateDInfo(textPtr)
    TkText *textPtr;        /* Overall information for text widget. */
{
    register TextDInfo *dInfoPtr;
    XGCValues gcValues;

    dInfoPtr = (TextDInfo *) ckalloc(sizeof(TextDInfo));
    Tcl_InitHashTable(&dInfoPtr->styleTable, sizeof(StyleValues)/sizeof(int));
    dInfoPtr->dLinePtr = NULL;
    dInfoPtr->copyGC = None;
    gcValues.graphics_exposures = True;
    dInfoPtr->scrollGC = Tk_GetGC(textPtr->tkwin, GCGraphicsExposures,
        &gcValues);
    dInfoPtr->topOfEof = 0;
    dInfoPtr->newCharOffset = 0;
    dInfoPtr->curPixelOffset = 0;
    dInfoPtr->maxLength = 0;
    dInfoPtr->xScrollFirst = -1;
    dInfoPtr->xScrollLast = -1;
    dInfoPtr->yScrollFirst = -1;
    dInfoPtr->yScrollLast = -1;
    dInfoPtr->scanMarkChar = 0;
    dInfoPtr->scanMarkX = 0;
    dInfoPtr->scanTotalScroll = 0;
    dInfoPtr->scanMarkY = 0;
    dInfoPtr->dLinesInvalidated = 0;
    dInfoPtr->flags = DINFO_OUT_OF_DATE;
    textPtr->dInfoPtr = dInfoPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * TkTextFreeDInfo --
 *
 *    This procedure is called to free up all of the private display
 *    information kept by this file for a text widget.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Lots of resources get freed.
 *
 *----------------------------------------------------------------------
 */

void
TkTextFreeDInfo(textPtr)
    TkText *textPtr;        /* Overall information for text widget. */
{
    register TextDInfo *dInfoPtr = textPtr->dInfoPtr;

    /*
     * Be careful to free up styleTable *after* freeing up all the
     * DLines, so that the hash table is still intact to free up the
     * style-related information from the lines.  Once the lines are
     * all free then styleTable will be empty.
     */

    FreeDLines(textPtr, dInfoPtr->dLinePtr, (DLine *) NULL, 1);
    Tcl_DeleteHashTable(&dInfoPtr->styleTable);
    if (dInfoPtr->copyGC != None) {
    Tk_FreeGC(textPtr->display, dInfoPtr->copyGC);
    }
    Tk_FreeGC(textPtr->display, dInfoPtr->scrollGC);
    if (dInfoPtr->flags & REDRAW_PENDING) {
    Tcl_CancelIdleCall(DisplayText, (ClientData) textPtr);
    }
    ckfree((char *) dInfoPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * GetStyle --
 *
 *    This procedure creates all the information needed to display
 *    text at a particular location.
 *
 * Results:
 *    The return value is a pointer to a TextStyle structure that
 *    corresponds to *sValuePtr.
 *
 * Side effects:
 *    A new entry may be created in the style table for the widget.
 *
 *----------------------------------------------------------------------
 */

static TextStyle *
GetStyle(textPtr, indexPtr)
    TkText *textPtr;        /* Overall information about text widget. */
    TkTextIndex *indexPtr;    /* The character in the text for which
                 * display information is wanted. */
{
    TkTextTag **tagPtrs;
    register TkTextTag *tagPtr;
    StyleValues styleValues;
    TextStyle *stylePtr;
    Tcl_HashEntry *hPtr;
    int numTags, new, i;
    XGCValues gcValues;
    unsigned long mask;

    /*
     * The variables below keep track of the highest-priority specification
     * that has occurred for each of the various fields of the StyleValues.
     */

    int borderPrio, borderWidthPrio, reliefPrio, bgStipplePrio;
    int fgPrio, fontPrio, fgStipplePrio;
    int underlinePrio, justifyPrio, offsetPrio;
    int lMargin1Prio, lMargin2Prio, rMarginPrio;
    int spacing1Prio, spacing2Prio, spacing3Prio;
    int overstrikePrio, tabPrio, wrapPrio;

    /*
     * Find out what tags are present for the character, then compute
     * a StyleValues structure corresponding to those tags (scan
     * through all of the tags, saving information for the highest-
     * priority tag).
     */

    tagPtrs = TkBTreeGetTags(indexPtr, &numTags);
    borderPrio = borderWidthPrio = reliefPrio = bgStipplePrio = -1;
    fgPrio = fontPrio = fgStipplePrio = -1;
    underlinePrio = justifyPrio = offsetPrio = -1;
    lMargin1Prio = lMargin2Prio = rMarginPrio = -1;
    spacing1Prio = spacing2Prio = spacing3Prio = -1;
    overstrikePrio = tabPrio = wrapPrio = -1;
    memset((VOID *) &styleValues, 0, sizeof(StyleValues));
    styleValues.relief = TK_RELIEF_FLAT;
    styleValues.fgColor = textPtr->fgColor;
    styleValues.tkfont = textPtr->tkfont;
    styleValues.justify = TK_JUSTIFY_LEFT;
    styleValues.spacing1 = textPtr->spacing1;
    styleValues.spacing2 = textPtr->spacing2;
    styleValues.spacing3 = textPtr->spacing3;
    styleValues.tabArrayPtr = textPtr->tabArrayPtr;
    styleValues.wrapMode = textPtr->wrapMode;
    for (i = 0 ; i < numTags; i++) {
    tagPtr = tagPtrs[i];

    /*
     * On Windows and Mac, we need to skip the selection tag if
     * we don't have focus.
     */

#ifndef ALWAYS_SHOW_SELECTION
    if ((tagPtr == textPtr->selTagPtr) && !(textPtr->flags & GOT_FOCUS)) {
        continue;
    }
#endif

    if ((tagPtr->border != NULL) && (tagPtr->priority > borderPrio)) {
        styleValues.border = tagPtr->border;
        borderPrio = tagPtr->priority;
    }
    if ((tagPtr->bdString != NULL)
        && (tagPtr->priority > borderWidthPrio)) {
        styleValues.borderWidth = tagPtr->borderWidth;
        borderWidthPrio = tagPtr->priority;
    }
    if ((tagPtr->reliefString != NULL)
        && (tagPtr->priority > reliefPrio)) {
        if (styleValues.border == NULL) {
        styleValues.border = textPtr->border;
        }
        styleValues.relief = tagPtr->relief;
        reliefPrio = tagPtr->priority;
    }
    if ((tagPtr->bgStipple != None)
        && (tagPtr->priority > bgStipplePrio)) {
        styleValues.bgStipple = tagPtr->bgStipple;
        bgStipplePrio = tagPtr->priority;
    }
    if ((tagPtr->fgColor != None) && (tagPtr->priority > fgPrio)) {
        styleValues.fgColor = tagPtr->fgColor;
        fgPrio = tagPtr->priority;
    }
    if ((tagPtr->tkfont != None) && (tagPtr->priority > fontPrio)) {
        styleValues.tkfont = tagPtr->tkfont;
        fontPrio = tagPtr->priority;
    }
    if ((tagPtr->fgStipple != None)
        && (tagPtr->priority > fgStipplePrio)) {
        styleValues.fgStipple = tagPtr->fgStipple;
        fgStipplePrio = tagPtr->priority;
    }
    if ((tagPtr->justifyString != NULL)
        && (tagPtr->priority > justifyPrio)) {
        styleValues.justify = tagPtr->justify;
        justifyPrio = tagPtr->priority;
    }
    if ((tagPtr->lMargin1String != NULL)
        && (tagPtr->priority > lMargin1Prio)) {
        styleValues.lMargin1 = tagPtr->lMargin1;
        lMargin1Prio = tagPtr->priority;
    }
    if ((tagPtr->lMargin2String != NULL)
        && (tagPtr->priority > lMargin2Prio)) {
        styleValues.lMargin2 = tagPtr->lMargin2;
        lMargin2Prio = tagPtr->priority;
    }
    if ((tagPtr->offsetString != NULL)
        && (tagPtr->priority > offsetPrio)) {
        styleValues.offset = tagPtr->offset;
        offsetPrio = tagPtr->priority;
    }
    if ((tagPtr->overstrikeString != NULL)
        && (tagPtr->priority > overstrikePrio)) {
        styleValues.overstrike = tagPtr->overstrike;
        overstrikePrio = tagPtr->priority;
    }
    if ((tagPtr->rMarginString != NULL)
        && (tagPtr->priority > rMarginPrio)) {
        styleValues.rMargin = tagPtr->rMargin;
        rMarginPrio = tagPtr->priority;
    }
    if ((tagPtr->spacing1String != NULL)
        && (tagPtr->priority > spacing1Prio)) {
        styleValues.spacing1 = tagPtr->spacing1;
        spacing1Prio = tagPtr->priority;
    }
    if ((tagPtr->spacing2String != NULL)
        && (tagPtr->priority > spacing2Prio)) {
        styleValues.spacing2 = tagPtr->spacing2;
        spacing2Prio = tagPtr->priority;
    }
    if ((tagPtr->spacing3String != NULL)
        && (tagPtr->priority > spacing3Prio)) {
        styleValues.spacing3 = tagPtr->spacing3;
        spacing3Prio = tagPtr->priority;
    }
    if ((tagPtr->tabString != NULL)
        && (tagPtr->priority > tabPrio)) {
        styleValues.tabArrayPtr = tagPtr->tabArrayPtr;
        tabPrio = tagPtr->priority;
    }
    if ((tagPtr->underlineString != NULL)
        && (tagPtr->priority > underlinePrio)) {
        styleValues.underline = tagPtr->underline;
        underlinePrio = tagPtr->priority;
    }
    if ((tagPtr->wrapMode != NULL)
        && (tagPtr->priority > wrapPrio)) {
        styleValues.wrapMode = tagPtr->wrapMode;
        wrapPrio = tagPtr->priority;
    }
    }
    if (tagPtrs != NULL) {
    ckfree((char *) tagPtrs);
    }

    /*
     * Use an existing style if there's one around that matches.
     */

    hPtr = Tcl_CreateHashEntry(&textPtr->dInfoPtr->styleTable,
        (char *) &styleValues, &new);
    if (!new) {
    stylePtr = (TextStyle *) Tcl_GetHashValue(hPtr);
    stylePtr->refCount++;
    return stylePtr;
    }

    /*
     * No existing style matched.  Make a new one.
     */

    stylePtr = (TextStyle *) ckalloc(sizeof(TextStyle));
    stylePtr->refCount = 1;
    if (styleValues.border != NULL) {
    gcValues.foreground = Tk_3DBorderColor(styleValues.border)->pixel;
    mask = GCForeground;
    if (styleValues.bgStipple != None) {
        gcValues.stipple = styleValues.bgStipple;
        gcValues.fill_style = FillStippled;
        mask |= GCStipple|GCFillStyle;
    }
    stylePtr->bgGC = Tk_GetGC(textPtr->tkwin, mask, &gcValues);
    } else {
    stylePtr->bgGC = None;
    }
    mask = GCForeground|GCFont;
    gcValues.foreground = styleValues.fgColor->pixel;
    gcValues.font = Tk_FontId(styleValues.tkfont);
    if (styleValues.fgStipple != None) {
    gcValues.stipple = styleValues.fgStipple;
    gcValues.fill_style = FillStippled;
    mask |= GCStipple|GCFillStyle;
    }
    stylePtr->fgGC = Tk_GetGC(textPtr->tkwin, mask, &gcValues);
    stylePtr->sValuePtr = (StyleValues *)
        Tcl_GetHashKey(&textPtr->dInfoPtr->styleTable, hPtr);
    stylePtr->hPtr = hPtr;
    Tcl_SetHashValue(hPtr, stylePtr);
    return stylePtr;
}

/*
 *----------------------------------------------------------------------
 *
 * FreeStyle --
 *
 *    This procedure is called when a TextStyle structure is no longer
 *    needed.  It decrements the reference count and frees up the
 *    space for the style structure if the reference count is 0.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The storage and other resources associated with the style
 *    are freed up if no-one's still using it.
 *
 *----------------------------------------------------------------------
 */

static void
FreeStyle(textPtr, stylePtr)
    TkText *textPtr;            /* Information about overall widget. */
    register TextStyle *stylePtr;    /* Information about style to free. */

{
    stylePtr->refCount--;
    if (stylePtr->refCount == 0) {
    if (stylePtr->bgGC != None) {
        Tk_FreeGC(textPtr->display, stylePtr->bgGC);
    }
    Tk_FreeGC(textPtr->display, stylePtr->fgGC);
    Tcl_DeleteHashEntry(stylePtr->hPtr);
    ckfree((char *) stylePtr);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * LayoutDLine --
 *
 *    This procedure generates a single DLine structure for a display
 *    line whose leftmost character is given by indexPtr.
 *
 * Results:
 *    The return value is a pointer to a DLine structure desribing the
 *    display line.  All fields are filled in and correct except for
 *    y and nextPtr.
 *
 * Side effects:
 *    Storage is allocated for the new DLine.
 *
 *----------------------------------------------------------------------
 */

static DLine *
LayoutDLine(textPtr, indexPtr)
    TkText *textPtr;        /* Overall information about text widget. */
    TkTextIndex *indexPtr;    /* Beginning of display line.  May not
                 * necessarily point to a character segment. */
{
    register DLine *dlPtr;        /* New display line. */
    TkTextSegment *segPtr;        /* Current segment in text. */
    TkTextDispChunk *lastChunkPtr;    /* Last chunk allocated so far
                     * for line. */
    TkTextDispChunk *chunkPtr;        /* Current chunk. */
    TkTextIndex curIndex;
    TkTextDispChunk *breakChunkPtr;    /* Chunk containing best word break
                     * point, if any. */
    TkTextIndex breakIndex;        /* Index of first character in
                     * breakChunkPtr. */
    int breakCharOffset;        /* Character within breakChunkPtr just
                     * to right of best break point. */
    int noCharsYet;            /* Non-zero means that no characters
                     * have been placed on the line yet. */
    int justify;            /* How to justify line: taken from
                     * style for first character in line. */
    int jIndent;            /* Additional indentation (beyond
                     * margins) due to justification. */
    int rMargin;            /* Right margin width for line. */
    Tk_Uid wrapMode;            /* Wrap mode to use for this line. */
    int x = 0, maxX = 0;        /* Initializations needed only to
                     * stop compiler warnings. */
    int wholeLine;            /* Non-zero means this display line
                     * runs to the end of the text line. */
    int tabIndex;            /* Index of the current tab stop. */
    int gotTab;                /* Non-zero means the current chunk
                     * contains a tab. */
    TkTextDispChunk *tabChunkPtr;    /* Pointer to the chunk containing
                     * the previous tab stop. */
    int maxChars;            /* Maximum number of characters to
                     * include in this chunk. */
    TkTextTabArray *tabArrayPtr;    /* Tab stops for line;  taken from
                     * style for first character on line. */
    int tabSize;            /* Number of pixels consumed by current
                     * tab stop. */
    TkTextDispChunk *lastCharChunkPtr;    /* Pointer to last chunk in display
                     * lines with numChars > 0.  Used to
                     * drop 0-sized chunks from the end
                     * of the line. */
    int offset, ascent, descent, code;
    StyleValues *sValuePtr;

    /*
     * Create and initialize a new DLine structure.
     */

    dlPtr = (DLine *) ckalloc(sizeof(DLine));
    dlPtr->index = *indexPtr;
    dlPtr->count = 0;
    dlPtr->y = 0;
    dlPtr->oldY = -1;
    dlPtr->height = 0;
    dlPtr->baseline = 0;
    dlPtr->chunkPtr = NULL;
    dlPtr->nextPtr = NULL;
    dlPtr->flags = NEW_LAYOUT;

    /*
     * Each iteration of the loop below creates one TkTextDispChunk for
     * the new display line.  The line will always have at least one
     * chunk (for the newline character at the end, if there's nothing
     * else available).
     */

    curIndex = *indexPtr;
    lastChunkPtr = NULL;
    chunkPtr = NULL;
    noCharsYet = 1;
    breakChunkPtr = NULL;
    breakCharOffset = 0;
    justify = TK_JUSTIFY_LEFT;
    tabIndex = -1;
    tabChunkPtr = NULL;
    tabArrayPtr = NULL;
    rMargin = 0;
    wrapMode = tkTextCharUid;
    tabSize = 0;
    lastCharChunkPtr = NULL;

    /*
     * Find the first segment to consider for the line.  Can't call
     * TkTextIndexToSeg for this because it won't return a segment
     * with zero size (such as the insertion cursor's mark).
     */

    for (offset = curIndex.charIndex, segPtr = curIndex.linePtr->segPtr;
        (offset > 0) && (offset >= segPtr->size);
        offset -= segPtr->size, segPtr = segPtr->nextPtr) {
    /* Empty loop body. */
    }

    while (segPtr != NULL) {
    if (segPtr->typePtr->layoutProc == NULL) {
        segPtr = segPtr->nextPtr;
        offset = 0;
        continue;
    }
    if (chunkPtr == NULL) {
        chunkPtr = (TkTextDispChunk *) ckalloc(sizeof(TkTextDispChunk));
        chunkPtr->nextPtr = NULL;
    }
    chunkPtr->stylePtr = GetStyle(textPtr, &curIndex);

    /*
     * Save style information such as justification and indentation,
     * up until the first character is encountered, then retain that
     * information for the rest of the line.
     */

    if (noCharsYet) {
        tabArrayPtr = chunkPtr->stylePtr->sValuePtr->tabArrayPtr;
        justify = chunkPtr->stylePtr->sValuePtr->justify;
        rMargin = chunkPtr->stylePtr->sValuePtr->rMargin;
        wrapMode = chunkPtr->stylePtr->sValuePtr->wrapMode;
        x = ((curIndex.charIndex == 0)
            ? chunkPtr->stylePtr->sValuePtr->lMargin1
            : chunkPtr->stylePtr->sValuePtr->lMargin2);
        if (wrapMode == tkTextNoneUid) {
        maxX = INT_MAX;
        } else {
        maxX = textPtr->dInfoPtr->maxX - textPtr->dInfoPtr->x
            - rMargin;
        if (maxX < x) {
            maxX = x;
        }
        }
    }

    /*
     * See if there is a tab in the current chunk; if so, only
     * layout characters up to (and including) the tab.
     */

    gotTab = 0;
    maxChars = segPtr->size - offset;
    if (justify == TK_JUSTIFY_LEFT) {
        if (segPtr->typePtr == &tkTextCharType) {
        char *p;

        for (p = segPtr->body.chars  + offset; *p != 0; p++) {
            if (*p == '\t') {
            maxChars = (p + 1 - segPtr->body.chars) - offset;
            gotTab = 1;
            break;
            }
        }
        }
    }

    chunkPtr->x = x;
    code = (*segPtr->typePtr->layoutProc)(textPtr, &curIndex, segPtr,
        offset, maxX-tabSize, maxChars, noCharsYet, wrapMode,
        chunkPtr);
    if (code <= 0) {
        FreeStyle(textPtr, chunkPtr->stylePtr);
        if (code < 0) {
        /*
         * This segment doesn't wish to display itself (e.g. most
         * marks).
         */

        segPtr = segPtr->nextPtr;
        offset = 0;
        continue;
        }

        /*
         * No characters from this segment fit in the window: this
         * means we're at the end of the display line.
         */

        if (chunkPtr != NULL) {
        ckfree((char *) chunkPtr);
        }
        break;
    }
    if (chunkPtr->numChars > 0) {
        noCharsYet = 0;
        lastCharChunkPtr = chunkPtr;
    }
    if (lastChunkPtr == NULL) {
        dlPtr->chunkPtr = chunkPtr;
    } else {
        lastChunkPtr->nextPtr = chunkPtr;
    }
    lastChunkPtr = chunkPtr;
    x += chunkPtr->width;
    if (chunkPtr->breakIndex > 0) {
        breakCharOffset = chunkPtr->breakIndex;
        breakIndex = curIndex;
        breakChunkPtr = chunkPtr;
    }
    if (chunkPtr->numChars != maxChars) {
        break;
    }

    /*
     * If we're at a new tab, adjust the layout for all the chunks
     * pertaining to the previous tab.  Also adjust the amount of
     * space left in the line to account for space that will be eaten
     * up by the tab.
     */

    if (gotTab) {
        if (tabIndex >= 0) {
        AdjustForTab(textPtr, tabArrayPtr, tabIndex, tabChunkPtr);
        x = chunkPtr->x + chunkPtr->width;
        }
        tabIndex++;
        tabChunkPtr = chunkPtr;
        tabSize = SizeOfTab(textPtr, tabArrayPtr, tabIndex, x, maxX);
        if (tabSize >= (maxX - x)) {
        break;
        }
    }
    curIndex.charIndex += chunkPtr->numChars;
    offset += chunkPtr->numChars;
    if (offset >= segPtr->size) {
        offset = 0;
        segPtr = segPtr->nextPtr;
    }
    chunkPtr = NULL;
    }
    if (noCharsYet) {
    panic("LayoutDLine couldn't place any characters on a line");
    }
    wholeLine = (segPtr == NULL);

    /*
     * We're at the end of the display line.  Throw away everything
     * after the most recent word break, if there is one;  this may
     * potentially require the last chunk to be layed out again.
     */

    if (breakChunkPtr == NULL) {
    /*
     * This code makes sure that we don't accidentally display
     * chunks with no characters at the end of the line (such as
     * the insertion cursor).  These chunks belong on the next
     * line.  So, throw away everything after the last chunk that
     * has characters in it.
     */

    breakChunkPtr = lastCharChunkPtr;
    breakCharOffset = breakChunkPtr->numChars;
    }
    if ((breakChunkPtr != NULL) && ((lastChunkPtr != breakChunkPtr)
        || (breakCharOffset != lastChunkPtr->numChars))) {
    while (1) {
        chunkPtr = breakChunkPtr->nextPtr;
        if (chunkPtr == NULL) {
        break;
        }
        FreeStyle(textPtr, chunkPtr->stylePtr);
        breakChunkPtr->nextPtr = chunkPtr->nextPtr;
        (*chunkPtr->undisplayProc)(textPtr, chunkPtr);
        ckfree((char *) chunkPtr);
    }
    if (breakCharOffset != breakChunkPtr->numChars) {
        (*breakChunkPtr->undisplayProc)(textPtr, breakChunkPtr);
        segPtr = TkTextIndexToSeg(&breakIndex, &offset);
        (*segPtr->typePtr->layoutProc)(textPtr, &breakIndex,
            segPtr, offset, maxX, breakCharOffset, 0,
            wrapMode, breakChunkPtr);
    }
    lastChunkPtr = breakChunkPtr;
    wholeLine = 0;
    }

    /*
     * Make tab adjustments for the last tab stop, if there is one.
     */

    if ((tabIndex >= 0) && (tabChunkPtr != NULL)) {
    AdjustForTab(textPtr, tabArrayPtr, tabIndex, tabChunkPtr);
    }

    /*
     * Make one more pass over the line to recompute various things
     * like its height, length, and total number of characters.  Also
     * modify the x-locations of chunks to reflect justification.
     * If we're not wrapping, I'm not sure what is the best way to
     * handle left and center justification:  should the total length,
     * for purposes of justification, be (a) the window width, (b)
     * the length of the longest line in the window, or (c) the length
     * of the longest line in the text?  (c) isn't available, (b) seems
     * weird, since it can change with vertical scrolling, so (a) is
     * what is implemented below.
     */

    if (wrapMode == tkTextNoneUid) {
    maxX = textPtr->dInfoPtr->maxX - textPtr->dInfoPtr->x - rMargin;
    }
    dlPtr->length = lastChunkPtr->x + lastChunkPtr->width;
    if (justify == TK_JUSTIFY_LEFT) {
    jIndent = 0;
    } else if (justify == TK_JUSTIFY_RIGHT) {
    jIndent = maxX - dlPtr->length;
    } else {
    jIndent = (maxX - dlPtr->length)/2;
    }
    ascent = descent = 0;
    for (chunkPtr = dlPtr->chunkPtr; chunkPtr != NULL;
        chunkPtr = chunkPtr->nextPtr) {
    chunkPtr->x += jIndent;
    dlPtr->count += chunkPtr->numChars;
    if (chunkPtr->minAscent > ascent) {
        ascent = chunkPtr->minAscent;
    }
    if (chunkPtr->minDescent > descent) {
        descent = chunkPtr->minDescent;
    }
    if (chunkPtr->minHeight > dlPtr->height) {
        dlPtr->height = chunkPtr->minHeight;
    }
    sValuePtr = chunkPtr->stylePtr->sValuePtr;
    if ((sValuePtr->borderWidth > 0)
        && (sValuePtr->relief != TK_RELIEF_FLAT)) {
        dlPtr->flags |= HAS_3D_BORDER;
    }
    }
    if (dlPtr->height < (ascent + descent)) {
    dlPtr->height = ascent + descent;
    dlPtr->baseline = ascent;
    } else {
    dlPtr->baseline = ascent + (dlPtr->height - ascent - descent)/2;
    }
    sValuePtr = dlPtr->chunkPtr->stylePtr->sValuePtr;
    if (dlPtr->index.charIndex == 0) {
    dlPtr->spaceAbove = sValuePtr->spacing1;
    } else {
    dlPtr->spaceAbove = sValuePtr->spacing2 - sValuePtr->spacing2/2;
    }
    if (wholeLine) {
    dlPtr->spaceBelow = sValuePtr->spacing3;
    } else {
    dlPtr->spaceBelow = sValuePtr->spacing2/2;
    }
    dlPtr->height += dlPtr->spaceAbove + dlPtr->spaceBelow;
    dlPtr->baseline += dlPtr->spaceAbove;

    /*
     * Recompute line length:  may have changed because of justification.
     */

    dlPtr->length = lastChunkPtr->x + lastChunkPtr->width;
    return dlPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * UpdateDisplayInfo --
 *
 *    This procedure is invoked to recompute some or all of the
 *    DLine structures for a text widget.  At the time it is called
 *    the DLine structures still left in the widget are guaranteed
 *    to be correct except that (a) the y-coordinates aren't
 *    necessarily correct, (b) there may be missing structures
 *    (the DLine structures get removed as soon as they are potentially
 *    out-of-date), and (c) DLine structures that don't start at the
 *    beginning of a line may be incorrect if previous information in
 *    the same line changed size in a way that moved a line boundary
 *    (DLines for any info that changed will have been deleted, but
 *    not DLines for unchanged info in the same text line).
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Upon return, the DLine information for textPtr correctly reflects
 *    the positions where characters will be displayed.  However, this
 *    procedure doesn't actually bring the display up-to-date.
 *
 *----------------------------------------------------------------------
 */

static void
UpdateDisplayInfo(textPtr)
    TkText *textPtr;            /* Text widget to update. */
{
    register TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    register DLine *dlPtr, *prevPtr;
    TkTextIndex index;
    TkTextLine *lastLinePtr;
    int y, maxY, pixelOffset, maxOffset;

    if (!(dInfoPtr->flags & DINFO_OUT_OF_DATE)) {
    return;
    }
    dInfoPtr->flags &= ~DINFO_OUT_OF_DATE;

    /*
     * Delete any DLines that are now above the top of the window.
     */

    index = textPtr->topIndex;
    dlPtr = FindDLine(dInfoPtr->dLinePtr, &index);
    if ((dlPtr != NULL) && (dlPtr != dInfoPtr->dLinePtr)) {
    FreeDLines(textPtr, dInfoPtr->dLinePtr, dlPtr, 1);
    }

    /*
     *--------------------------------------------------------------
     * Scan through the contents of the window from top to bottom,
     * recomputing information for lines that are missing.
     *--------------------------------------------------------------
     */

    lastLinePtr = TkBTreeFindLine(textPtr->tree,
        TkBTreeNumLines(textPtr->tree));
    dlPtr = dInfoPtr->dLinePtr;
    prevPtr = NULL;
    y = dInfoPtr->y;
    maxY = dInfoPtr->maxY;
    while (1) {
    register DLine *newPtr;

    if (index.linePtr == lastLinePtr) {
        break;
    }

    /*
     * There are three possibilities right now:
     * (a) the next DLine (dlPtr) corresponds exactly to the next
     *     information we want to display: just use it as-is.
     * (b) the next DLine corresponds to a different line, or to
     *     a segment that will be coming later in the same line:
     *     leave this DLine alone in the hopes that we'll be able
     *     to use it later, then create a new DLine in front of
     *     it.
     * (c) the next DLine corresponds to a segment in the line we
     *     want, but it's a segment that has already been processed
     *     or will never be processed.  Delete the DLine and try
     *     again.
     *
     * One other twist on all this.  It's possible for 3D borders
     * to interact between lines (see DisplayLineBackground) so if
     * a line is relayed out and has styles with 3D borders, its
     * neighbors have to be redrawn if they have 3D borders too,
     * since the interactions could have changed (the neighbors
     * don't have to be relayed out, just redrawn).
     */

    if ((dlPtr == NULL) || (dlPtr->index.linePtr != index.linePtr)) {
        /*
         * Case (b) -- must make new DLine.
         */

        makeNewDLine:
        if (tkTextDebug) {
        char string[TK_POS_CHARS];

        /*
         * Debugging is enabled, so keep a log of all the lines
         * that were re-layed out.  The test suite uses this
         * information.
         */

        TkTextPrintIndex(&index, string);
        Tcl_SetVar2(textPtr->interp, "tk_textRelayout", (char *) NULL,
            string,
            TCL_GLOBAL_ONLY|TCL_APPEND_VALUE|TCL_LIST_ELEMENT);
        }
        newPtr = LayoutDLine(textPtr, &index);
        if (prevPtr == NULL) {
        dInfoPtr->dLinePtr = newPtr;
        } else {
        prevPtr->nextPtr = newPtr;
        if (prevPtr->flags & HAS_3D_BORDER) {
            prevPtr->oldY = -1;
        }
        }
        newPtr->nextPtr = dlPtr;
        dlPtr = newPtr;
    } else {
        /*
         * DlPtr refers to the line we want.  Next check the
         * index within the line.
         */

        if (index.charIndex == dlPtr->index.charIndex) {
        /*
         * Case (a) -- can use existing display line as-is.
         */

        if ((dlPtr->flags & HAS_3D_BORDER) && (prevPtr != NULL)
            && (prevPtr->flags & (NEW_LAYOUT))) {
            dlPtr->oldY = -1;
        }
        goto lineOK;
        }
        if (index.charIndex < dlPtr->index.charIndex) {
        goto makeNewDLine;
        }

        /*
         * Case (c) -- dlPtr is useless.  Discard it and start
         * again with the next display line.
         */

        newPtr = dlPtr->nextPtr;
        FreeDLines(textPtr, dlPtr, newPtr, 0);
        dlPtr = newPtr;
        if (prevPtr != NULL) {
        prevPtr->nextPtr = newPtr;
        } else {
        dInfoPtr->dLinePtr = newPtr;
        }
        continue;
    }

    /*
     * Advance to the start of the next line.
     */

    lineOK:
    dlPtr->y = y;
    y += dlPtr->height;
    TkTextIndexForwChars(&index, dlPtr->count, &index);
    prevPtr = dlPtr;
    dlPtr = dlPtr->nextPtr;

    /*
     * If we switched text lines, delete any DLines left for the
     * old text line.
     */

    if (index.linePtr != prevPtr->index.linePtr) {
        register DLine *nextPtr;

        nextPtr = dlPtr;
        while ((nextPtr != NULL)
            && (nextPtr->index.linePtr == prevPtr->index.linePtr)) {
        nextPtr = nextPtr->nextPtr;
        }
        if (nextPtr != dlPtr) {
        FreeDLines(textPtr, dlPtr, nextPtr, 0);
        prevPtr->nextPtr = nextPtr;
        dlPtr = nextPtr;
        }
    }

    /*
     * It's important to have the following check here rather than in
     * the while statement for the loop, so that there's always at least
     * one DLine generated, regardless of how small the window is.  This
     * keeps a lot of other code from breaking.
     */

    if (y >= maxY) {
        break;
    }
    }

    /*
     * Delete any DLine structures that don't fit on the screen.
     */

    FreeDLines(textPtr, dlPtr, (DLine *) NULL, 1);

    /*
     *--------------------------------------------------------------
     * If there is extra space at the bottom of the window (because
     * we've hit the end of the text), then bring in more lines at
     * the top of the window, if there are any, to fill in the view.
     *--------------------------------------------------------------
     */

    if (y < maxY) {
    int lineNum, spaceLeft, charsToCount;
    DLine *lowestPtr;

    /*
     * Layout an entire text line (potentially > 1 display line),
     * then link in as many display lines as fit without moving
     * the bottom line out of the window.  Repeat this until
     * all the extra space has been used up or we've reached the
     * beginning of the text.
     */

    spaceLeft = maxY - y;
    lineNum = TkBTreeLineIndex(dInfoPtr->dLinePtr->index.linePtr);
    charsToCount = dInfoPtr->dLinePtr->index.charIndex;
    if (charsToCount == 0) {
        charsToCount = INT_MAX;
        lineNum--;
    }
    for ( ; (lineNum >= 0) && (spaceLeft > 0); lineNum--) {
        index.linePtr = TkBTreeFindLine(textPtr->tree, lineNum);
        index.charIndex = 0;
        lowestPtr = NULL;
        do {
        dlPtr = LayoutDLine(textPtr, &index);
        dlPtr->nextPtr = lowestPtr;
        lowestPtr = dlPtr;
        TkTextIndexForwChars(&index, dlPtr->count, &index);
        charsToCount -= dlPtr->count;
        } while ((charsToCount > 0)
            && (index.linePtr == lowestPtr->index.linePtr));

        /*
         * Scan through the display lines from the bottom one up to
         * the top one.
         */

        while (lowestPtr != NULL) {
        dlPtr = lowestPtr;
        spaceLeft -= dlPtr->height;
        if (spaceLeft < 0) {
            break;
        }
        lowestPtr = dlPtr->nextPtr;
        dlPtr->nextPtr = dInfoPtr->dLinePtr;
        dInfoPtr->dLinePtr = dlPtr;
        if (tkTextDebug) {
            char string[TK_POS_CHARS];

            TkTextPrintIndex(&dlPtr->index, string);
            Tcl_SetVar2(textPtr->interp, "tk_textRelayout",
                (char *) NULL, string,
                TCL_GLOBAL_ONLY|TCL_APPEND_VALUE|TCL_LIST_ELEMENT);
        }
        }
        FreeDLines(textPtr, lowestPtr, (DLine *) NULL, 0);
        charsToCount = INT_MAX;
    }

    /*
     * Now we're all done except that the y-coordinates in all the
     * DLines are wrong and the top index for the text is wrong.
     * Update them.
     */

    textPtr->topIndex = dInfoPtr->dLinePtr->index;
    y = dInfoPtr->y;
    for (dlPtr = dInfoPtr->dLinePtr; dlPtr != NULL;
        dlPtr = dlPtr->nextPtr) {
        if (y > dInfoPtr->maxY) {
        panic("Added too many new lines in UpdateDisplayInfo");
        }
        dlPtr->y = y;
        y += dlPtr->height;
    }
    }

    /*
     *--------------------------------------------------------------
     * If the old top or bottom line has scrolled elsewhere on the
     * screen, we may not be able to re-use its old contents by
     * copying bits (e.g., a beveled edge that was drawn when it was
     * at the top or bottom won't be drawn when the line is in the
     * middle and its neighbor has a matching background).  Similarly,
     * if the new top or bottom line came from somewhere else on the
     * screen, we may not be able to copy the old bits.
     *--------------------------------------------------------------
     */

    dlPtr = dInfoPtr->dLinePtr;
    if ((dlPtr->flags & HAS_3D_BORDER) && !(dlPtr->flags & TOP_LINE)) {
    dlPtr->oldY = -1;
    }
    while (1) {
    if ((dlPtr->flags & TOP_LINE) && (dlPtr != dInfoPtr->dLinePtr)
        && (dlPtr->flags & HAS_3D_BORDER)) {
        dlPtr->oldY = -1;
    }
    if ((dlPtr->flags & BOTTOM_LINE) && (dlPtr->nextPtr != NULL)
        && (dlPtr->flags & HAS_3D_BORDER)) {
        dlPtr->oldY = -1;
    }
    if (dlPtr->nextPtr == NULL) {
        if ((dlPtr->flags & HAS_3D_BORDER)
            && !(dlPtr->flags & BOTTOM_LINE)) {
        dlPtr->oldY = -1;
        }
        dlPtr->flags &= ~TOP_LINE;
        dlPtr->flags |= BOTTOM_LINE;
        break;
    }
    dlPtr->flags &= ~(TOP_LINE|BOTTOM_LINE);
    dlPtr = dlPtr->nextPtr;
    }
    dInfoPtr->dLinePtr->flags |= TOP_LINE;

    /*
     * Arrange for scrollbars to be updated.
     */

    textPtr->flags |= UPDATE_SCROLLBARS;

    /*
     *--------------------------------------------------------------
     * Deal with horizontal scrolling:
     * 1. If there's empty space to the right of the longest line,
     *    shift the screen to the right to fill in the empty space.
     * 2. If the desired horizontal scroll position has changed,
     *    force a full redisplay of all the lines in the widget.
     * 3. If the wrap mode isn't "none" then re-scroll to the base
     *    position.
     *--------------------------------------------------------------
     */

    dInfoPtr->maxLength = 0;
    for (dlPtr = dInfoPtr->dLinePtr; dlPtr != NULL;
        dlPtr = dlPtr->nextPtr) {
    if (dlPtr->length > dInfoPtr->maxLength) {
        dInfoPtr->maxLength = dlPtr->length;
    }
    }
    maxOffset = (dInfoPtr->maxLength - (dInfoPtr->maxX - dInfoPtr->x)
        + textPtr->charWidth - 1)/textPtr->charWidth;
    if (dInfoPtr->newCharOffset > maxOffset) {
    dInfoPtr->newCharOffset = maxOffset;
    }
    if (dInfoPtr->newCharOffset < 0) {
    dInfoPtr->newCharOffset = 0;
    }
    pixelOffset = dInfoPtr->newCharOffset * textPtr->charWidth;
    if (pixelOffset != dInfoPtr->curPixelOffset) {
    dInfoPtr->curPixelOffset = pixelOffset;
    for (dlPtr = dInfoPtr->dLinePtr; dlPtr != NULL;
        dlPtr = dlPtr->nextPtr) {
        dlPtr->oldY = -1;
    }
    }
}

/*
 *----------------------------------------------------------------------
 *
 * FreeDLines --
 *
 *    This procedure is called to free up all of the resources
 *    associated with one or more DLine structures.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Memory gets freed and various other resources are released.
 *
 *----------------------------------------------------------------------
 */

static void
FreeDLines(textPtr, firstPtr, lastPtr, unlink)
    TkText *textPtr;            /* Information about overall text
                     * widget. */
    register DLine *firstPtr;        /* Pointer to first DLine to free up. */
    DLine *lastPtr;            /* Pointer to DLine just after last
                     * one to free (NULL means everything
                     * starting with firstPtr). */
    int unlink;                /* 1 means DLines are currently linked
                     * into the list rooted at
                     * textPtr->dInfoPtr->dLinePtr and
                     * they have to be unlinked.  0 means
                     * just free without unlinking. */
{
    register TkTextDispChunk *chunkPtr, *nextChunkPtr;
    register DLine *nextDLinePtr;

    if (unlink) {
    if (textPtr->dInfoPtr->dLinePtr == firstPtr) {
        textPtr->dInfoPtr->dLinePtr = lastPtr;
    } else {
        register DLine *prevPtr;
        for (prevPtr = textPtr->dInfoPtr->dLinePtr;
            prevPtr->nextPtr != firstPtr; prevPtr = prevPtr->nextPtr) {
        /* Empty loop body. */
        }
        prevPtr->nextPtr = lastPtr;
    }
    }
    while (firstPtr != lastPtr) {
    nextDLinePtr = firstPtr->nextPtr;
    for (chunkPtr = firstPtr->chunkPtr; chunkPtr != NULL;
        chunkPtr = nextChunkPtr) {
        if (chunkPtr->undisplayProc != NULL) {
        (*chunkPtr->undisplayProc)(textPtr, chunkPtr);
        }
        FreeStyle(textPtr, chunkPtr->stylePtr);
        nextChunkPtr = chunkPtr->nextPtr;
        ckfree((char *) chunkPtr);
    }
    ckfree((char *) firstPtr);
    firstPtr = nextDLinePtr;
    }
    textPtr->dInfoPtr->dLinesInvalidated = 1;
}

/*
 *----------------------------------------------------------------------
 *
 * DisplayDLine --
 *
 *    This procedure is invoked to draw a single line on the
 *    screen.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The line given by dlPtr is drawn at its correct position in
 *    textPtr's window.  Note that this is one *display* line, not
 *    one *text* line.
 *
 *----------------------------------------------------------------------
 */

static void
DisplayDLine(textPtr, dlPtr, prevPtr, pixmap)
    TkText *textPtr;        /* Text widget in which to draw line. */
    register DLine *dlPtr;    /* Information about line to draw. */
    DLine *prevPtr;        /* Line just before one to draw, or NULL
                 * if dlPtr is the top line. */
    Pixmap pixmap;        /* Pixmap to use for double-buffering.
                 * Caller must make sure it's large enough
                 * to hold line. */
{
    register TkTextDispChunk *chunkPtr;
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    Display *display;
    int height, x;

    /*
     * First, clear the area of the line to the background color for the
     * text widget.
     */

    display = Tk_Display(textPtr->tkwin);
    Tk_Fill3DRectangle(textPtr->tkwin, pixmap, textPtr->border, 0, 0,
        Tk_Width(textPtr->tkwin), dlPtr->height, 0, TK_RELIEF_FLAT);

    /*
     * Next, draw background information for the whole line.
     */

    DisplayLineBackground(textPtr, dlPtr, prevPtr, pixmap);

    /*
     * Make another pass through all of the chunks to redraw the
     * insertion cursor, if it is visible on this line.  Must do
     * it here rather than in the foreground pass below because
     * otherwise a wide insertion cursor will obscure the character
     * to its left.
     */

    if (textPtr->state == tkNormalUid) {
    for (chunkPtr = dlPtr->chunkPtr; (chunkPtr != NULL);
        chunkPtr = chunkPtr->nextPtr) {
        x = chunkPtr->x + dInfoPtr->x - dInfoPtr->curPixelOffset;
        if (chunkPtr->displayProc == TkTextInsertDisplayProc) {
        (*chunkPtr->displayProc)(chunkPtr, x, dlPtr->spaceAbove,
            dlPtr->height - dlPtr->spaceAbove - dlPtr->spaceBelow,
            dlPtr->baseline - dlPtr->spaceAbove, display, pixmap,
            dlPtr->y + dlPtr->spaceAbove);
        }
    }
    }

    /*
     * Make yet another pass through all of the chunks to redraw all of
     * foreground information.  Note:  we have to call the displayProc
     * even for chunks that are off-screen.  This is needed, for
     * example, so that embedded windows can be unmapped in this case.
     * Conve
     */

    for (chunkPtr = dlPtr->chunkPtr; (chunkPtr != NULL);
        chunkPtr = chunkPtr->nextPtr) {
    if (chunkPtr->displayProc == TkTextInsertDisplayProc) {
        /*
         * Already displayed the insertion cursor above.  Don't
         * do it again here.
         */

        continue;
    }
    x = chunkPtr->x + dInfoPtr->x - dInfoPtr->curPixelOffset;
    if ((x + chunkPtr->width <= 0) || (x >= dInfoPtr->maxX)) {
        /*
         * Note:  we have to call the displayProc even for chunks
         * that are off-screen.  This is needed, for example, so
         * that embedded windows can be unmapped in this case.
         * Display the chunk at a coordinate that can be clearly
         * identified by the displayProc as being off-screen to
         * the left (the displayProc may not be able to tell if
         * something is off to the right).
         */

        (*chunkPtr->displayProc)(chunkPtr, -chunkPtr->width,
            dlPtr->spaceAbove,
            dlPtr->height - dlPtr->spaceAbove - dlPtr->spaceBelow,
            dlPtr->baseline - dlPtr->spaceAbove, display, pixmap,
            dlPtr->y + dlPtr->spaceAbove);
    } else {
        (*chunkPtr->displayProc)(chunkPtr, x, dlPtr->spaceAbove,
            dlPtr->height - dlPtr->spaceAbove - dlPtr->spaceBelow,
            dlPtr->baseline - dlPtr->spaceAbove, display, pixmap,
            dlPtr->y + dlPtr->spaceAbove);
    }
    if (dInfoPtr->dLinesInvalidated) {
        return;
    }
    }

    /*
     * Copy the pixmap onto the screen.  If this is the last line on
     * the screen then copy a piece of the line, so that it doesn't
     * overflow into the border area.  Another special trick:  copy the
     * padding area to the left of the line;  this is because the
     * insertion cursor sometimes overflows onto that area and we want
     * to get as much of the cursor as possible.
     */

    height = dlPtr->height;
    if ((height + dlPtr->y) > dInfoPtr->maxY) {
    height = dInfoPtr->maxY - dlPtr->y;
    }
    XCopyArea(display, pixmap, Tk_WindowId(textPtr->tkwin), dInfoPtr->copyGC,
        dInfoPtr->x, 0, (unsigned) (dInfoPtr->maxX - dInfoPtr->x),
        (unsigned) height, dInfoPtr->x, dlPtr->y);
    linesRedrawn++;
}

/*
 *--------------------------------------------------------------
 *
 * DisplayLineBackground --
 *
 *    This procedure is called to fill in the background for
 *    a display line.  It draws 3D borders cleverly so that
 *    adjacent chunks with the same style (whether on the same
 *    line or different lines) have a single 3D border around
 *    the whole region.
 *
 * Results:
 *    There is no return value.  Pixmap is filled in with background
 *    information for dlPtr.
 *
 * Side effects:
 *    None.
 *
 *--------------------------------------------------------------
 */

static void
DisplayLineBackground(textPtr, dlPtr, prevPtr, pixmap)
    TkText *textPtr;        /* Text widget containing line. */
    register DLine *dlPtr;    /* Information about line to draw. */
    DLine *prevPtr;        /* Line just above dlPtr, or NULL if dlPtr
                 * is the top-most line in the window. */
    Pixmap pixmap;        /* Pixmap to use for double-buffering.
                 * Caller must make sure it's large enough
                 * to hold line.  Caller must also have
                 * filled it with the background color for
                 * the widget. */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    TkTextDispChunk *chunkPtr;  /* Pointer to chunk in the current line. */
    TkTextDispChunk *chunkPtr2;    /* Pointer to chunk in the line above or
                 * below the current one.  NULL if we're to
                 * the left of or to the right of the chunks
                 * in the line. */
    TkTextDispChunk *nextPtr2;    /* Next chunk after chunkPtr2 (it's not the
                 * same as chunkPtr2->nextPtr in the case
                 * where chunkPtr2 is NULL because the line
                 * is indented). */
    int leftX;            /* The left edge of the region we're
                 * currently working on. */
    int leftXIn;        /* 1 means beveled edge at leftX slopes right
                 * as it goes down, 0 means it slopes left
                 * as it goes down. */
    int rightX;            /* Right edge of chunkPtr. */
    int rightX2;        /* Right edge of chunkPtr2. */
    int matchLeft;        /* Does the style of this line match that
                 * of its neighbor just to the left of
                 * the current x coordinate? */
    int matchRight;        /* Does line's style match its neighbor
                 * just to the right of the current x-coord? */
    int minX, maxX, xOffset;
    StyleValues *sValuePtr;
    Display *display;

    /*
     * Pass 1: scan through dlPtr from left to right.  For each range of
     * chunks with the same style, draw the main background for the style
     * plus the vertical parts of the 3D borders (the left and right
     * edges).
     */

    display = Tk_Display(textPtr->tkwin);
    minX = dInfoPtr->curPixelOffset;
    xOffset = dInfoPtr->x - minX;
    maxX = minX + dInfoPtr->maxX - dInfoPtr->x;
    chunkPtr = dlPtr->chunkPtr;

    /*
     * Note A: in the following statement, and a few others later in
     * this file marked with "See Note A above", the right side of the
     * assignment was replaced with 0 on 6/18/97.  This has the effect
     * of highlighting the empty space to the left of a line whenever
     * the leftmost character of the line is highlighted.  This way,
     * multi-line highlights always line up along their left edges.
     * However, this may look funny in the case where a single word is
     * highlighted. To undo the change, replace "leftX = 0" with "leftX
     * = chunkPtr->x" and "rightX2 = 0" with "rightX2 = nextPtr2->x"
     * here and at all the marked points below.  This restores the old
     * behavior where empty space to the left of a line is not
     * highlighted, leaving a ragged left edge for multi-line
     * highlights.
     */

    leftX = 0;
    for (; leftX < maxX; chunkPtr = chunkPtr->nextPtr) {
    if ((chunkPtr->nextPtr != NULL)
        && SAME_BACKGROUND(chunkPtr->nextPtr->stylePtr,
        chunkPtr->stylePtr)) {
        continue;
    }
    sValuePtr = chunkPtr->stylePtr->sValuePtr;
    rightX = chunkPtr->x + chunkPtr->width;
    if ((chunkPtr->nextPtr == NULL) && (rightX < maxX)) {
        rightX = maxX;
    }
    if (chunkPtr->stylePtr->bgGC != None) {
        XFillRectangle(display, pixmap, chunkPtr->stylePtr->bgGC,
            leftX + xOffset, 0, (unsigned int) (rightX - leftX),
            (unsigned int) dlPtr->height);
        if (sValuePtr->relief != TK_RELIEF_FLAT) {
        Tk_3DVerticalBevel(textPtr->tkwin, pixmap, sValuePtr->border,
            leftX + xOffset, 0, sValuePtr->borderWidth,
            dlPtr->height, 1, sValuePtr->relief);
        Tk_3DVerticalBevel(textPtr->tkwin, pixmap, sValuePtr->border,
            rightX - sValuePtr->borderWidth + xOffset,
            0, sValuePtr->borderWidth, dlPtr->height, 0,
            sValuePtr->relief);
        }
    }
    leftX = rightX;
    }

    /*
     * Pass 2: draw the horizontal bevels along the top of the line.  To
     * do this, scan through dlPtr from left to right while simultaneously
     * scanning through the line just above dlPtr.  ChunkPtr2 and nextPtr2
     * refer to two adjacent chunks in the line above.
     */

    chunkPtr = dlPtr->chunkPtr;
    leftX = 0;                /* See Note A above. */
    leftXIn = 1;
    rightX = chunkPtr->x + chunkPtr->width;
    if ((chunkPtr->nextPtr == NULL) && (rightX < maxX)) {
    rightX = maxX;
    }
    chunkPtr2 = NULL;
    if (prevPtr != NULL) {
    /*
     * Find the chunk in the previous line that covers leftX.
     */

    nextPtr2 = prevPtr->chunkPtr;
    rightX2 = 0;            /* See Note A above. */
    while (rightX2 <= leftX) {
        chunkPtr2 = nextPtr2;
        if (chunkPtr2 == NULL) {
        break;
        }
        nextPtr2 = chunkPtr2->nextPtr;
        rightX2 = chunkPtr2->x + chunkPtr2->width;
        if (nextPtr2 == NULL) {
        rightX2 = INT_MAX;
        }
    }
    } else {
    nextPtr2 = NULL;
    rightX2 = INT_MAX;
    }

    while (leftX < maxX) {
    matchLeft = (chunkPtr2 != NULL)
        && SAME_BACKGROUND(chunkPtr2->stylePtr, chunkPtr->stylePtr);
    sValuePtr = chunkPtr->stylePtr->sValuePtr;
    if (rightX <= rightX2) {
        /*
         * The chunk in our line is about to end.  If its style
         * changes then draw the bevel for the current style.
         */

        if ((chunkPtr->nextPtr == NULL)
            || !SAME_BACKGROUND(chunkPtr->stylePtr,
            chunkPtr->nextPtr->stylePtr)) {
        if (!matchLeft && (sValuePtr->relief != TK_RELIEF_FLAT)) {
            Tk_3DHorizontalBevel(textPtr->tkwin, pixmap,
                sValuePtr->border, leftX + xOffset, 0,
                rightX - leftX, sValuePtr->borderWidth, leftXIn,
                1, 1, sValuePtr->relief);
        }
        leftX = rightX;
        leftXIn = 1;

        /*
         * If the chunk in the line above is also ending at
         * the same point then advance to the next chunk in
         * that line.
         */

        if ((rightX == rightX2) && (chunkPtr2 != NULL)) {
            goto nextChunk2;
        }
        }
        chunkPtr = chunkPtr->nextPtr;
        if (chunkPtr == NULL) {
        break;
        }
        rightX = chunkPtr->x + chunkPtr->width;
        if ((chunkPtr->nextPtr == NULL) && (rightX < maxX)) {
        rightX = maxX;
        }
        continue;
    }

    /*
     * The chunk in the line above is ending at an x-position where
     * there is no change in the style of the current line.  If the
     * style above matches the current line on one side of the change
     * but not on the other, we have to draw an L-shaped piece of
     * bevel.
     */

    matchRight = (nextPtr2 != NULL)
        && SAME_BACKGROUND(nextPtr2->stylePtr, chunkPtr->stylePtr);
    if (matchLeft && !matchRight) {
        if (sValuePtr->relief != TK_RELIEF_FLAT) {
        Tk_3DVerticalBevel(textPtr->tkwin, pixmap, sValuePtr->border,
            rightX2 - sValuePtr->borderWidth + xOffset, 0,
            sValuePtr->borderWidth, sValuePtr->borderWidth, 0,
            sValuePtr->relief);
        }
        leftX = rightX2 - sValuePtr->borderWidth;
        leftXIn = 0;
    } else if (!matchLeft && matchRight
        && (sValuePtr->relief != TK_RELIEF_FLAT)) {
        Tk_3DVerticalBevel(textPtr->tkwin, pixmap, sValuePtr->border,
            rightX2 + xOffset, 0, sValuePtr->borderWidth,
            sValuePtr->borderWidth, 1, sValuePtr->relief);
        Tk_3DHorizontalBevel(textPtr->tkwin, pixmap, sValuePtr->border,
            leftX + xOffset, 0, rightX2 + sValuePtr->borderWidth -leftX,
            sValuePtr->borderWidth, leftXIn, 0, 1,
            sValuePtr->relief);
    }

    nextChunk2:
    chunkPtr2 = nextPtr2;
    if (chunkPtr2 == NULL) {
        rightX2 = INT_MAX;
    } else {
        nextPtr2 = chunkPtr2->nextPtr;
        rightX2 = chunkPtr2->x + chunkPtr2->width;
        if (nextPtr2 == NULL) {
        rightX2 = INT_MAX;
        }
    }
    }
    /*
     * Pass 3: draw the horizontal bevels along the bottom of the line.
     * This uses the same approach as pass 2.
     */

    chunkPtr = dlPtr->chunkPtr;
    leftX = 0;                /* See Note A above. */
    leftXIn = 0;
    rightX = chunkPtr->x + chunkPtr->width;
    if ((chunkPtr->nextPtr == NULL) && (rightX < maxX)) {
    rightX = maxX;
    }
    chunkPtr2 = NULL;
    if (dlPtr->nextPtr != NULL) {
    /*
     * Find the chunk in the previous line that covers leftX.
     */

    nextPtr2 = dlPtr->nextPtr->chunkPtr;
    rightX2 = 0;            /* See Note A above. */
    while (rightX2 <= leftX) {
        chunkPtr2 = nextPtr2;
        if (chunkPtr2 == NULL) {
        break;
        }
        nextPtr2 = chunkPtr2->nextPtr;
        rightX2 = chunkPtr2->x + chunkPtr2->width;
        if (nextPtr2 == NULL) {
        rightX2 = INT_MAX;
        }
    }
    } else {
    nextPtr2 = NULL;
    rightX2 = INT_MAX;
    }

    while (leftX < maxX) {
    matchLeft = (chunkPtr2 != NULL)
        && SAME_BACKGROUND(chunkPtr2->stylePtr, chunkPtr->stylePtr);
    sValuePtr = chunkPtr->stylePtr->sValuePtr;
    if (rightX <= rightX2) {
        if ((chunkPtr->nextPtr == NULL)
            || !SAME_BACKGROUND(chunkPtr->stylePtr,
            chunkPtr->nextPtr->stylePtr)) {
        if (!matchLeft && (sValuePtr->relief != TK_RELIEF_FLAT)) {
            Tk_3DHorizontalBevel(textPtr->tkwin, pixmap,
                sValuePtr->border, leftX + xOffset,
                dlPtr->height - sValuePtr->borderWidth,
                rightX - leftX, sValuePtr->borderWidth, leftXIn,
                0, 0, sValuePtr->relief);
        }
        leftX = rightX;
        leftXIn = 0;
        if ((rightX == rightX2) && (chunkPtr2 != NULL)) {
            goto nextChunk2b;
        }
        }
        chunkPtr = chunkPtr->nextPtr;
        if (chunkPtr == NULL) {
        break;
        }
        rightX = chunkPtr->x + chunkPtr->width;
        if ((chunkPtr->nextPtr == NULL) && (rightX < maxX)) {
        rightX = maxX;
        }
        continue;
    }

    matchRight = (nextPtr2 != NULL)
        && SAME_BACKGROUND(nextPtr2->stylePtr, chunkPtr->stylePtr);
    if (matchLeft && !matchRight) {
        if (sValuePtr->relief != TK_RELIEF_FLAT) {
        Tk_3DVerticalBevel(textPtr->tkwin, pixmap, sValuePtr->border,
            rightX2 - sValuePtr->borderWidth + xOffset,
            dlPtr->height - sValuePtr->borderWidth,
            sValuePtr->borderWidth, sValuePtr->borderWidth, 0,
            sValuePtr->relief);
        }
        leftX = rightX2 - sValuePtr->borderWidth;
        leftXIn = 1;
    } else if (!matchLeft && matchRight
        && (sValuePtr->relief != TK_RELIEF_FLAT)) {
        Tk_3DVerticalBevel(textPtr->tkwin, pixmap, sValuePtr->border,
            rightX2 + xOffset, dlPtr->height - sValuePtr->borderWidth,
            sValuePtr->borderWidth, sValuePtr->borderWidth,
            1, sValuePtr->relief);
        Tk_3DHorizontalBevel(textPtr->tkwin, pixmap, sValuePtr->border,
            leftX + xOffset, dlPtr->height - sValuePtr->borderWidth,
            rightX2 + sValuePtr->borderWidth - leftX,
            sValuePtr->borderWidth, leftXIn, 1, 0, sValuePtr->relief);
    }

    nextChunk2b:
    chunkPtr2 = nextPtr2;
    if (chunkPtr2 == NULL) {
        rightX2 = INT_MAX;
    } else {
        nextPtr2 = chunkPtr2->nextPtr;
        rightX2 = chunkPtr2->x + chunkPtr2->width;
        if (nextPtr2 == NULL) {
        rightX2 = INT_MAX;
        }
    }
    }
}

/*
 *----------------------------------------------------------------------
 *
 * DisplayText --
 *
 *    This procedure is invoked as a when-idle handler to update the
 *    display.  It only redisplays the parts of the text widget that
 *    are out of date.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Information is redrawn on the screen.
 *
 *----------------------------------------------------------------------
 */

static void
DisplayText(clientData)
    ClientData clientData;    /* Information about widget. */
{
    register TkText *textPtr = (TkText *) clientData;
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    Tk_Window tkwin;
    register DLine *dlPtr;
    DLine *prevPtr;
    Pixmap pixmap;
    int maxHeight, borders;
    int bottomY = 0;        /* Initialization needed only to stop
                 * compiler warnings. */
    Tcl_Interp *interp;

    if (textPtr->tkwin == NULL) {

    /*
     * The widget has been deleted.  Don't do anything.
     */

    return;
    }

    interp = textPtr->interp;
    Tcl_Preserve((ClientData) interp);

    if (tkTextDebug) {
    Tcl_SetVar2(interp, "tk_textRelayout", (char *) NULL, "",
                TCL_GLOBAL_ONLY);
    }

    if (textPtr->tkwin == NULL) {

    /*
     * The widget has been deleted.  Don't do anything.
     */

        goto end;
    }

    if (!Tk_IsMapped(textPtr->tkwin) || (dInfoPtr->maxX <= dInfoPtr->x)
        || (dInfoPtr->maxY <= dInfoPtr->y)) {
    UpdateDisplayInfo(textPtr);
    dInfoPtr->flags &= ~REDRAW_PENDING;
    goto doScrollbars;
    }
    numRedisplays++;
    if (tkTextDebug) {
    Tcl_SetVar2(interp, "tk_textRedraw", (char *) NULL, "",
                TCL_GLOBAL_ONLY);
    }

    if (textPtr->tkwin == NULL) {

    /*
     * The widget has been deleted.  Don't do anything.
     */

    goto end;
    }

    /*
     * Choose a new current item if that is needed (this could cause
     * event handlers to be invoked, hence the preserve/release calls
     * and the loop, since the handlers could conceivably necessitate
     * yet another current item calculation).  The tkwin check is because
     * the whole window could go away in the Tcl_Release call.
     */

    while (dInfoPtr->flags & REPICK_NEEDED) {
    Tcl_Preserve((ClientData) textPtr);
    dInfoPtr->flags &= ~REPICK_NEEDED;
    TkTextPickCurrent(textPtr, &textPtr->pickEvent);
    tkwin = textPtr->tkwin;
    Tcl_Release((ClientData) textPtr);
    if (tkwin == NULL) {
        goto end;
    }
    }

    /*
     * First recompute what's supposed to be displayed.
     */

    UpdateDisplayInfo(textPtr);
    dInfoPtr->dLinesInvalidated = 0;

    /*
     * See if it's possible to bring some parts of the screen up-to-date
     * by scrolling (copying from other parts of the screen).
     */

    for (dlPtr = dInfoPtr->dLinePtr; dlPtr != NULL; dlPtr = dlPtr->nextPtr) {
    register DLine *dlPtr2;
    int offset, height, y, oldY;
    TkRegion damageRgn;

    if ((dlPtr->oldY == -1) || (dlPtr->y == dlPtr->oldY)
        || ((dlPtr->oldY + dlPtr->height) > dInfoPtr->maxY)) {
        continue;
    }

    /*
     * This line is already drawn somewhere in the window so it only
     * needs to be copied to its new location.  See if there's a group
     * of lines that can all be copied together.
     */

    offset = dlPtr->y - dlPtr->oldY;
    height = dlPtr->height;
    y = dlPtr->y;
    for (dlPtr2 = dlPtr->nextPtr; dlPtr2 != NULL;
        dlPtr2 = dlPtr2->nextPtr) {
        if ((dlPtr2->oldY == -1)
            || ((dlPtr2->oldY + offset) != dlPtr2->y)
            || ((dlPtr2->oldY + dlPtr2->height) > dInfoPtr->maxY)) {
        break;
        }
        height += dlPtr2->height;
    }

    /*
     * Reduce the height of the area being copied if necessary to
     * avoid overwriting the border area.
     */

    if ((y + height) > dInfoPtr->maxY) {
        height = dInfoPtr->maxY -y;
    }
    oldY = dlPtr->oldY;

    /*
     * Update the lines we are going to scroll to show that they
     * have been copied.
     */

    while (1) {
        dlPtr->oldY = dlPtr->y;
        if (dlPtr->nextPtr == dlPtr2) {
        break;
        }
        dlPtr = dlPtr->nextPtr;
    }

    /*
     * Scan through the lines following the copied ones to see if
     * we are going to overwrite them with the copy operation.
     * If so, mark them for redisplay.
     */

    for ( ; dlPtr2 != NULL; dlPtr2 = dlPtr2->nextPtr) {
        if ((dlPtr2->oldY != -1)
            && ((dlPtr2->oldY + dlPtr2->height) > y)
            && (dlPtr2->oldY < (y + height))) {
        dlPtr2->oldY = -1;
        }
    }

    /*
     * Now scroll the lines.  This may generate damage which we
     * handle by calling TextInvalidateRegion to mark the display
     * blocks as stale.
     */

    damageRgn = TkCreateRegion();
    if (TkScrollWindow(textPtr->tkwin, dInfoPtr->scrollGC,
        dInfoPtr->x, oldY,
        (dInfoPtr->maxX - dInfoPtr->x), height,
        0, y - oldY, damageRgn)) {
        TextInvalidateRegion(textPtr, damageRgn);
    }
    numCopies++;
    TkDestroyRegion(damageRgn);
    }

    /*
     * Clear the REDRAW_PENDING flag here.  This is actually pretty
     * tricky.  We want to wait until *after* doing the scrolling,
     * since that could generate more areas to redraw and don't
     * want to reschedule a redisplay for them.  On the other hand,
     * we can't wait until after all the redisplaying, because the
     * act of redisplaying could actually generate more redisplays
     * (e.g. in the case of a nested window with event bindings triggered
     * by redisplay).
     */

    dInfoPtr->flags &= ~REDRAW_PENDING;

    /*
     * Redraw the borders if that's needed.
     */

    if (dInfoPtr->flags & REDRAW_BORDERS) {
    if (tkTextDebug) {
        Tcl_SetVar2(interp, "tk_textRedraw", (char *) NULL, "borders",
            TCL_GLOBAL_ONLY|TCL_APPEND_VALUE|TCL_LIST_ELEMENT);
    }

        if (textPtr->tkwin == NULL) {

        /*
             * The widget has been deleted.  Don't do anything.
             */

            goto end;
        }

    Tk_Draw3DRectangle(textPtr->tkwin, Tk_WindowId(textPtr->tkwin),
        textPtr->border, textPtr->highlightWidth,
        textPtr->highlightWidth,
        Tk_Width(textPtr->tkwin) - 2*textPtr->highlightWidth,
        Tk_Height(textPtr->tkwin) - 2*textPtr->highlightWidth,
        textPtr->borderWidth, textPtr->relief);
    if (textPtr->highlightWidth != 0) {
        GC gc;

        if (textPtr->flags & GOT_FOCUS) {
        gc = Tk_GCForColor(textPtr->highlightColorPtr,
            Tk_WindowId(textPtr->tkwin));
        } else {
        gc = Tk_GCForColor(textPtr->highlightBgColorPtr,
            Tk_WindowId(textPtr->tkwin));
        }
        Tk_DrawFocusHighlight(textPtr->tkwin, gc, textPtr->highlightWidth,
            Tk_WindowId(textPtr->tkwin));
    }
    borders = textPtr->borderWidth + textPtr->highlightWidth;
    if (textPtr->padY > 0) {
        Tk_Fill3DRectangle(textPtr->tkwin, Tk_WindowId(textPtr->tkwin),
            textPtr->border, borders, borders,
            Tk_Width(textPtr->tkwin) - 2*borders, textPtr->padY,
            0, TK_RELIEF_FLAT);
        Tk_Fill3DRectangle(textPtr->tkwin, Tk_WindowId(textPtr->tkwin),
            textPtr->border, borders,
            Tk_Height(textPtr->tkwin) - borders - textPtr->padY,
            Tk_Width(textPtr->tkwin) - 2*borders,
            textPtr->padY, 0, TK_RELIEF_FLAT);
    }
    if (textPtr->padX > 0) {
        Tk_Fill3DRectangle(textPtr->tkwin, Tk_WindowId(textPtr->tkwin),
            textPtr->border, borders, borders + textPtr->padY,
            textPtr->padX,
            Tk_Height(textPtr->tkwin) - 2*borders -2*textPtr->padY,
            0, TK_RELIEF_FLAT);
        Tk_Fill3DRectangle(textPtr->tkwin, Tk_WindowId(textPtr->tkwin),
            textPtr->border,
            Tk_Width(textPtr->tkwin) - borders - textPtr->padX,
            borders + textPtr->padY, textPtr->padX,
            Tk_Height(textPtr->tkwin) - 2*borders -2*textPtr->padY,
            0, TK_RELIEF_FLAT);
    }
    dInfoPtr->flags &= ~REDRAW_BORDERS;
    }

    /*
     * Now we have to redraw the lines that couldn't be updated by
     * scrolling.  First, compute the height of the largest line and
     * allocate an off-screen pixmap to use for double-buffered
     * displays.
     */

    maxHeight = -1;
    for (dlPtr = dInfoPtr->dLinePtr; dlPtr != NULL;
        dlPtr = dlPtr->nextPtr) {
    if ((dlPtr->height > maxHeight) && (dlPtr->oldY != dlPtr->y)) {
        maxHeight = dlPtr->height;
    }
    bottomY = dlPtr->y + dlPtr->height;
    }
    if (maxHeight > dInfoPtr->maxY) {
    maxHeight = dInfoPtr->maxY;
    }
    if (maxHeight > 0) {
    pixmap = Tk_GetPixmap(Tk_Display(textPtr->tkwin),
        Tk_WindowId(textPtr->tkwin), Tk_Width(textPtr->tkwin),
        maxHeight, Tk_Depth(textPtr->tkwin));
    for (prevPtr = NULL, dlPtr = textPtr->dInfoPtr->dLinePtr;
        (dlPtr != NULL) && (dlPtr->y < dInfoPtr->maxY);
        prevPtr = dlPtr, dlPtr = dlPtr->nextPtr) {
        if (dlPtr->oldY != dlPtr->y) {
        if (tkTextDebug) {
            char string[TK_POS_CHARS];
            TkTextPrintIndex(&dlPtr->index, string);
            Tcl_SetVar2(textPtr->interp, "tk_textRedraw",
                (char *) NULL, string,
                TCL_GLOBAL_ONLY|TCL_APPEND_VALUE|TCL_LIST_ELEMENT);
        }
        DisplayDLine(textPtr, dlPtr, prevPtr, pixmap);
        if (dInfoPtr->dLinesInvalidated) {
            Tk_FreePixmap(Tk_Display(textPtr->tkwin), pixmap);
            return;
        }
        dlPtr->oldY = dlPtr->y;
        dlPtr->flags &= ~NEW_LAYOUT;
        }
    }
    Tk_FreePixmap(Tk_Display(textPtr->tkwin), pixmap);
    }

    /*
     * See if we need to refresh the part of the window below the
     * last line of text (if there is any such area).  Refresh the
     * padding area on the left too, since the insertion cursor might
     * have been displayed there previously).
     */

    if (dInfoPtr->topOfEof > dInfoPtr->maxY) {
    dInfoPtr->topOfEof = dInfoPtr->maxY;
    }
    if (bottomY < dInfoPtr->topOfEof) {
    if (tkTextDebug) {
        Tcl_SetVar2(textPtr->interp, "tk_textRedraw",
            (char *) NULL, "eof",
            TCL_GLOBAL_ONLY|TCL_APPEND_VALUE|TCL_LIST_ELEMENT);
    }

        if (textPtr->tkwin == NULL) {

        /*
             * The widget has been deleted.  Don't do anything.
             */

            goto end;
        }

    Tk_Fill3DRectangle(textPtr->tkwin, Tk_WindowId(textPtr->tkwin),
        textPtr->border, dInfoPtr->x - textPtr->padX, bottomY,
        dInfoPtr->maxX - (dInfoPtr->x - textPtr->padX),
        dInfoPtr->topOfEof-bottomY, 0, TK_RELIEF_FLAT);
    }
    dInfoPtr->topOfEof = bottomY;

    doScrollbars:

    /*
     * Update the vertical scrollbar, if there is one.  Note:  it's
     * important to clear REDRAW_PENDING here, just in case the
     * scroll procedure does something that requires redisplay.
     */

    if (textPtr->flags & UPDATE_SCROLLBARS) {
    textPtr->flags &= ~UPDATE_SCROLLBARS;
    if (textPtr->yScrollCmd != NULL) {
        GetYView(textPtr->interp, textPtr, 1);
    }

        if (textPtr->tkwin == NULL) {

        /*
             * The widget has been deleted.  Don't do anything.
             */

            goto end;
        }

    /*
     * Update the horizontal scrollbar, if any.
     */

    if (textPtr->xScrollCmd != NULL) {
        GetXView(textPtr->interp, textPtr, 1);
    }
    }

end:
    Tcl_Release((ClientData) interp);
}

/*
 *----------------------------------------------------------------------
 *
 * TkTextEventuallyRepick --
 *
 *    This procedure is invoked whenever something happens that
 *    could change the current character or the tags associated
 *    with it.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    A repick is scheduled as an idle handler.
 *
 *----------------------------------------------------------------------
 */

    /* ARGSUSED */
void
TkTextEventuallyRepick(textPtr)
    TkText *textPtr;        /* Widget record for text widget. */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;

    dInfoPtr->flags |= REPICK_NEEDED;
    if (!(dInfoPtr->flags & REDRAW_PENDING)) {
    dInfoPtr->flags |= REDRAW_PENDING;
    Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkTextRedrawRegion --
 *
 *    This procedure is invoked to schedule a redisplay for a given
 *    region of a text widget.  The redisplay itself may not occur
 *    immediately:  it's scheduled as a when-idle handler.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Information will eventually be redrawn on the screen.
 *
 *----------------------------------------------------------------------
 */

    /* ARGSUSED */
void
TkTextRedrawRegion(textPtr, x, y, width, height)
    TkText *textPtr;        /* Widget record for text widget. */
    int x, y;            /* Coordinates of upper-left corner of area
                 * to be redrawn, in pixels relative to
                 * textPtr's window. */
    int width, height;        /* Width and height of area to be redrawn. */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    TkRegion damageRgn = TkCreateRegion();
    XRectangle rect;

    rect.x = x;
    rect.y = y;
    rect.width = width;
    rect.height = height;
    TkUnionRectWithRegion(&rect, damageRgn, damageRgn);

    TextInvalidateRegion(textPtr, damageRgn);

    if (!(dInfoPtr->flags & REDRAW_PENDING)) {
    dInfoPtr->flags |= REDRAW_PENDING;
    Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
    }
    TkDestroyRegion(damageRgn);
}

/*
 *----------------------------------------------------------------------
 *
 * TextInvalidateRegion --
 *
 *    Mark a region of text as invalid.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Updates the display information for the text widget.
 *
 *----------------------------------------------------------------------
 */

static void
TextInvalidateRegion(textPtr, region)
    TkText *textPtr;        /* Widget record for text widget. */
    TkRegion region;        /* Region of area to redraw. */
{
    register DLine *dlPtr;
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    int maxY, inset;
    XRectangle rect;

    /*
     * Find all lines that overlap the given region and mark them for
     * redisplay.
     */

    TkClipBox(region, &rect);
    maxY = rect.y + rect.height;
    for (dlPtr = dInfoPtr->dLinePtr; dlPtr != NULL;
        dlPtr = dlPtr->nextPtr) {
    if ((dlPtr->oldY != -1) && (TkRectInRegion(region, rect.x, dlPtr->y,
        rect.width, (unsigned int) dlPtr->height) != RectangleOut)) {
        dlPtr->oldY = -1;
    }
    }
    if (dInfoPtr->topOfEof < maxY) {
    dInfoPtr->topOfEof = maxY;
    }

    /*
     * Schedule the redisplay operation if there isn't one already
     * scheduled.
     */

    inset = textPtr->borderWidth + textPtr->highlightWidth;
    if ((rect.x < (inset + textPtr->padX))
        || (rect.y < (inset + textPtr->padY))
        || ((int) (rect.x + rect.width) > (Tk_Width(textPtr->tkwin)
            - inset - textPtr->padX))
        || (maxY > (Tk_Height(textPtr->tkwin) - inset - textPtr->padY))) {
    dInfoPtr->flags |= REDRAW_BORDERS;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkTextChanged --
 *
 *    This procedure is invoked when info in a text widget is about
 *    to be modified in a way that changes how it is displayed (e.g.
 *    characters were inserted or deleted, or tag information was
 *    changed).  This procedure must be called *before* a change is
 *    made, so that indexes in the display information are still
 *    valid.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The range of character between index1Ptr (inclusive) and
 *    index2Ptr (exclusive) will be redisplayed at some point in the
 *    future (the actual redisplay is scheduled as a when-idle handler).
 *
 *----------------------------------------------------------------------
 */

void
TkTextChanged(textPtr, index1Ptr, index2Ptr)
    TkText *textPtr;        /* Widget record for text widget. */
    TkTextIndex *index1Ptr;    /* Index of first character to redisplay. */
    TkTextIndex *index2Ptr;    /* Index of character just after last one
                 * to redisplay. */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    DLine *firstPtr, *lastPtr;
    TkTextIndex rounded;

    /*
     * Schedule both a redisplay and a recomputation of display information.
     * It's done here rather than the end of the procedure for two reasons:
     *
     * 1. If there are no display lines to update we'll want to return
     *    immediately, well before the end of the procedure.
     * 2. It's important to arrange for the redisplay BEFORE calling
     *    FreeDLines.  The reason for this is subtle and has to do with
     *    embedded windows.  The chunk delete procedure for an embedded
     *    window will schedule an idle handler to unmap the window.
     *    However, we want the idle handler for redisplay to be called
     *    first, so that it can put the embedded window back on the screen
     *    again (if appropriate).  This will prevent the window from ever
     *    being unmapped, and thereby avoid flashing.
     */

    if (!(dInfoPtr->flags & REDRAW_PENDING)) {
    Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
    }
    dInfoPtr->flags |= REDRAW_PENDING|DINFO_OUT_OF_DATE|REPICK_NEEDED;

    /*
     * Find the DLines corresponding to index1Ptr and index2Ptr.  There
     * is one tricky thing here, which is that we have to relayout in
     * units of whole text lines:  round index1Ptr back to the beginning
     * of its text line, and include all the display lines after index2,
     * up to the end of its text line.  This is necessary because the
     * indices stored in the display lines will no longer be valid.  It's
     * also needed because any edit could change the way lines wrap.
     */

    rounded = *index1Ptr;
    rounded.charIndex = 0;
    firstPtr = FindDLine(dInfoPtr->dLinePtr, &rounded);
    if (firstPtr == NULL) {
    return;
    }
    lastPtr = FindDLine(dInfoPtr->dLinePtr, index2Ptr);
    while ((lastPtr != NULL)
        && (lastPtr->index.linePtr == index2Ptr->linePtr)) {
    lastPtr = lastPtr->nextPtr;
    }

    /*
     * Delete all the DLines from firstPtr up to but not including lastPtr.
     */

    FreeDLines(textPtr, firstPtr, lastPtr, 1);
}

/*
 *----------------------------------------------------------------------
 *
 * TkTextRedrawTag --
 *
 *    This procedure is invoked to request a redraw of all characters
 *    in a given range that have a particular tag on or off.  It's
 *    called, for example, when tag options change.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Information on the screen may be redrawn, and the layout of
 *    the screen may change.
 *
 *----------------------------------------------------------------------
 */

void
TkTextRedrawTag(textPtr, index1Ptr, index2Ptr, tagPtr, withTag)
    TkText *textPtr;        /* Widget record for text widget. */
    TkTextIndex *index1Ptr;    /* First character in range to consider
                 * for redisplay.  NULL means start at
                 * beginning of text. */
    TkTextIndex *index2Ptr;    /* Character just after last one to consider
                 * for redisplay.  NULL means process all
                 * the characters in the text. */
    TkTextTag *tagPtr;        /* Information about tag. */
    int withTag;        /* 1 means redraw characters that have the
                 * tag, 0 means redraw those without. */
{
    register DLine *dlPtr;
    DLine *endPtr;
    int tagOn;
    TkTextSearch search;
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    TkTextIndex *curIndexPtr;
    TkTextIndex endOfText, *endIndexPtr;

    /*
     * Round up the starting position if it's before the first line
     * visible on the screen (we only care about what's on the screen).
     */

    dlPtr = dInfoPtr->dLinePtr;
    if (dlPtr == NULL) {
    return;
    }
    if ((index1Ptr == NULL) || (TkTextIndexCmp(&dlPtr->index, index1Ptr) > 0)) {
    index1Ptr = &dlPtr->index;
    }

    /*
     * Set the stopping position if it wasn't specified.
     */

    if (index2Ptr == NULL) {
    index2Ptr = TkTextMakeIndex(textPtr->tree,
        TkBTreeNumLines(textPtr->tree), 0, &endOfText);
    }

    /*
     * Initialize a search through all transitions on the tag, starting
     * with the first transition where the tag's current state is different
     * from what it will eventually be.
     */

    TkBTreeStartSearch(index1Ptr, index2Ptr, tagPtr, &search);
    /*
     * Make our own curIndex because at this point search.curIndex
     * may not equal index1Ptr->curIndex in the case the first tag toggle
     * comes after index1Ptr (See the use of FindTagStart in TkBTreeStartSearch)
     */
    curIndexPtr = index1Ptr;
    tagOn = TkBTreeCharTagged(index1Ptr, tagPtr);
    if (tagOn != withTag) {
    if (!TkBTreeNextTag(&search)) {
        return;
    }
    curIndexPtr = &search.curIndex;
    }

    /*
     * Schedule a redisplay and layout recalculation if they aren't
     * already pending.  This has to be done before calling FreeDLines,
     * for the reason given in TkTextChanged.
     */

    if (!(dInfoPtr->flags & REDRAW_PENDING)) {
    Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
    }
    dInfoPtr->flags |= REDRAW_PENDING|DINFO_OUT_OF_DATE|REPICK_NEEDED;

    /*
     * Each loop through the loop below is for one range of characters
     * where the tag's current state is different than its eventual
     * state.  At the top of the loop, search contains information about
     * the first character in the range.
     */

    while (1) {
    /*
     * Find the first DLine structure in the range.  Note: if the
     * desired character isn't the first in its text line, then look
     * for the character just before it instead.  This is needed to
     * handle the case where the first character of a wrapped
     * display line just got smaller, so that it now fits on the
     * line before:  need to relayout the line containing the
     * previous character.
     */

    if (curIndexPtr->charIndex == 0) {
        dlPtr = FindDLine(dlPtr, curIndexPtr);
    } else {
        TkTextIndex tmp;

        tmp = *curIndexPtr;
        tmp.charIndex -= 1;
        dlPtr = FindDLine(dlPtr, &tmp);
    }
    if (dlPtr == NULL) {
        break;
    }

    /*
     * Find the first DLine structure that's past the end of the range.
     */

    if (!TkBTreeNextTag(&search)) {
        endIndexPtr = index2Ptr;
    } else {
        curIndexPtr = &search.curIndex;
        endIndexPtr = curIndexPtr;
    }
    endPtr = FindDLine(dlPtr, endIndexPtr);
    if ((endPtr != NULL) && (endPtr->index.linePtr == endIndexPtr->linePtr)
        && (endPtr->index.charIndex < endIndexPtr->charIndex)) {
        endPtr = endPtr->nextPtr;
    }

    /*
     * Delete all of the display lines in the range, so that they'll
     * be re-layed out and redrawn.
     */

    FreeDLines(textPtr, dlPtr, endPtr, 1);
    dlPtr = endPtr;

    /*
     * Find the first text line in the next range.
     */

    if (!TkBTreeNextTag(&search)) {
        break;
    }
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkTextRelayoutWindow --
 *
 *    This procedure is called when something has happened that
 *    invalidates the whole layout of characters on the screen, such
 *    as a change in a configuration option for the overall text
 *    widget or a change in the window size.  It causes all display
 *    information to be recomputed and the window to be redrawn.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    All the display information will be recomputed for the window
 *    and the window will be redrawn.
 *
 *----------------------------------------------------------------------
 */

void
TkTextRelayoutWindow(textPtr)
    TkText *textPtr;        /* Widget record for text widget. */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    GC new;
    XGCValues gcValues;

    /*
     * Schedule the window redisplay.  See TkTextChanged for the
     * reason why this has to be done before any calls to FreeDLines.
     */

    if (!(dInfoPtr->flags & REDRAW_PENDING)) {
    Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
    }
    dInfoPtr->flags |= REDRAW_PENDING|REDRAW_BORDERS|DINFO_OUT_OF_DATE
        |REPICK_NEEDED;

    /*
     * (Re-)create the graphics context for drawing the traversal
     * highlight.
     */

    gcValues.graphics_exposures = False;
    new = Tk_GetGC(textPtr->tkwin, GCGraphicsExposures, &gcValues);
    if (dInfoPtr->copyGC != None) {
    Tk_FreeGC(textPtr->display, dInfoPtr->copyGC);
    }
    dInfoPtr->copyGC = new;

    /*
     * Throw away all the current layout information.
     */

    FreeDLines(textPtr, dInfoPtr->dLinePtr, (DLine *) NULL, 1);
    dInfoPtr->dLinePtr = NULL;

    /*
     * Recompute some overall things for the layout.  Even if the
     * window gets very small, pretend that there's at least one
     * pixel of drawing space in it.
     */

    if (textPtr->highlightWidth < 0) {
    textPtr->highlightWidth = 0;
    }
    dInfoPtr->x = textPtr->highlightWidth + textPtr->borderWidth
        + textPtr->padX;
    dInfoPtr->y = textPtr->highlightWidth + textPtr->borderWidth
        + textPtr->padY;
    dInfoPtr->maxX = Tk_Width(textPtr->tkwin) - textPtr->highlightWidth
        - textPtr->borderWidth - textPtr->padX;
    if (dInfoPtr->maxX <= dInfoPtr->x) {
    dInfoPtr->maxX = dInfoPtr->x + 1;
    }
    dInfoPtr->maxY = Tk_Height(textPtr->tkwin) - textPtr->highlightWidth
        - textPtr->borderWidth - textPtr->padY;
    if (dInfoPtr->maxY <= dInfoPtr->y) {
    dInfoPtr->maxY = dInfoPtr->y + 1;
    }
    dInfoPtr->topOfEof = dInfoPtr->maxY;

    /*
     * If the upper-left character isn't the first in a line, recompute
     * it.  This is necessary because a change in the window's size
     * or options could change the way lines wrap.
     */

    if (textPtr->topIndex.charIndex != 0) {
    MeasureUp(textPtr, &textPtr->topIndex, 0, &textPtr->topIndex);
    }

    /*
     * Invalidate cached scrollbar positions, so that scrollbars
     * sliders will be udpated.
     */

    dInfoPtr->xScrollFirst = dInfoPtr->xScrollLast = -1;
    dInfoPtr->yScrollFirst = dInfoPtr->yScrollLast = -1;
}

/*
 *----------------------------------------------------------------------
 *
 * TkTextSetYView --
 *
 *    This procedure is called to specify what lines are to be
 *    displayed in a text widget.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The display will (eventually) be updated so that the position
 *    given by "indexPtr" is visible on the screen at the position
 *    determined by "pickPlace".
 *
 *----------------------------------------------------------------------
 */

void
TkTextSetYView(textPtr, indexPtr, pickPlace)
    TkText *textPtr;        /* Widget record for text widget. */
    TkTextIndex *indexPtr;    /* Position that is to appear somewhere
                 * in the view. */
    int pickPlace;        /* 0 means topLine must appear at top of
                 * screen.  1 means we get to pick where it
                 * appears:  minimize screen motion or else
                 * display line at center of screen. */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    register DLine *dlPtr;
    int bottomY, close, lineIndex;
    TkTextIndex tmpIndex, rounded;
    Tk_FontMetrics fm;

    /*
     * If the specified position is the extra line at the end of the
     * text, round it back to the last real line.
     */

    lineIndex = TkBTreeLineIndex(indexPtr->linePtr);
    if (lineIndex == TkBTreeNumLines(indexPtr->tree)) {
    TkTextIndexBackChars(indexPtr, 1, &rounded);
    indexPtr = &rounded;
    }

    if (!pickPlace) {
    /*
     * The specified position must go at the top of the screen.
     * Just leave all the DLine's alone: we may be able to reuse
     * some of the information that's currently on the screen
     * without redisplaying it all.
     */

    if (indexPtr->charIndex == 0) {
        textPtr->topIndex = *indexPtr;
    } else {
        MeasureUp(textPtr, indexPtr, 0, &textPtr->topIndex);
    }
    goto scheduleUpdate;
    }

    /*
     * We have to pick where to display the index.  First, bring
     * the display information up to date and see if the index will be
     * completely visible in the current screen configuration.  If so
     * then there's nothing to do.
     */

    if (dInfoPtr->flags & DINFO_OUT_OF_DATE) {
    UpdateDisplayInfo(textPtr);
    }
    dlPtr = FindDLine(dInfoPtr->dLinePtr, indexPtr);
    if (dlPtr != NULL) {
    if ((dlPtr->y + dlPtr->height) > dInfoPtr->maxY) {
        /*
         * Part of the line hangs off the bottom of the screen;
         * pretend the whole line is off-screen.
         */

        dlPtr = NULL;
    } else if ((dlPtr->index.linePtr == indexPtr->linePtr)
        && (dlPtr->index.charIndex <= indexPtr->charIndex)) {
        return;
    }
    }

    /*
     * The desired line isn't already on-screen.  Figure out what
     * it means to be "close" to the top or bottom of the screen.
     * Close means within 1/3 of the screen height or within three
     * lines, whichever is greater.  Add one extra line also, to
     * account for the way MeasureUp rounds.
     */

    Tk_GetFontMetrics(textPtr->tkfont, &fm);
    bottomY = (dInfoPtr->y + dInfoPtr->maxY + fm.linespace)/2;
    close = (dInfoPtr->maxY - dInfoPtr->y)/3;
    if (close < 3*fm.linespace) {
    close = 3*fm.linespace;
    }
    close += fm.linespace;
    if (dlPtr != NULL) {
    /*
     * The desired line is above the top of screen.  If it is
     * "close" to the top of the window then make it the top
     * line on the screen.
     */

    MeasureUp(textPtr, &textPtr->topIndex, close, &tmpIndex);
    if (TkTextIndexCmp(&tmpIndex, indexPtr) <= 0) {
        MeasureUp(textPtr, indexPtr, 0, &textPtr->topIndex);
        goto scheduleUpdate;
    }
    } else {
    /*
     * The desired line is below the bottom of the screen.  If it is
     * "close" to the bottom of the screen then position it at the
     * bottom of the screen.
     */

    MeasureUp(textPtr, indexPtr, close, &tmpIndex);
    if (FindDLine(dInfoPtr->dLinePtr, &tmpIndex) != NULL) {
        bottomY = dInfoPtr->maxY - dInfoPtr->y;
    }
    }

    /*
     * Our job now is to arrange the display so that indexPtr appears
     * as low on the screen as possible but with its bottom no lower
     * than bottomY.  BottomY is the bottom of the window if the
     * desired line is just below the current screen, otherwise it
     * is a half-line lower than the center of the window.
     */

    MeasureUp(textPtr, indexPtr, bottomY, &textPtr->topIndex);

    scheduleUpdate:
    if (!(dInfoPtr->flags & REDRAW_PENDING)) {
    Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
    }
    dInfoPtr->flags |= REDRAW_PENDING|DINFO_OUT_OF_DATE|REPICK_NEEDED;
}

/*
 *--------------------------------------------------------------
 *
 * MeasureUp --
 *
 *    Given one index, find the index of the first character
 *    on the highest display line that would be displayed no more
 *    than "distance" pixels above the given index.
 *
 * Results:
 *    *dstPtr is filled in with the index of the first character
 *    on a display line.  The display line is found by measuring
 *    up "distance" pixels above the pixel just below an imaginary
 *    display line that contains srcPtr.  If the display line
 *    that covers this coordinate actually extends above the
 *    coordinate, then return the index of the next lower line
 *    instead (i.e. the returned index will be completely visible
 *    at or below the given y-coordinate).
 *
 * Side effects:
 *    None.
 *
 *--------------------------------------------------------------
 */

static void
MeasureUp(textPtr, srcPtr, distance, dstPtr)
    TkText *textPtr;        /* Text widget in which to measure. */
    TkTextIndex *srcPtr;    /* Index of character from which to start
                 * measuring. */
    int distance;        /* Vertical distance in pixels measured
                 * from the pixel just below the lowest
                 * one in srcPtr's line. */
    TkTextIndex *dstPtr;    /* Index to fill in with result. */
{
    int lineNum;        /* Number of current line. */
    int charsToCount;        /* Maximum number of characters to measure
                 * in current line. */
    TkTextIndex bestIndex;    /* Best candidate seen so far for result. */
    TkTextIndex index;
    DLine *dlPtr, *lowestPtr;
    int noBestYet;        /* 1 means bestIndex hasn't been set. */

    noBestYet = 1;
    charsToCount = srcPtr->charIndex + 1;
    index.tree = srcPtr->tree;
    for (lineNum = TkBTreeLineIndex(srcPtr->linePtr); lineNum >= 0;
        lineNum--) {
    /*
     * Layout an entire text line (potentially > 1 display line).
     * For the first line, which contains srcPtr, only layout the
     * part up through srcPtr (charsToCount is non-infinite to
     * accomplish this).  Make a list of all the display lines
     * in backwards order (the lowest DLine on the screen is first
     * in the list).
     */

    index.linePtr = TkBTreeFindLine(srcPtr->tree, lineNum);
    index.charIndex = 0;
    lowestPtr = NULL;
    do {
        dlPtr = LayoutDLine(textPtr, &index);
        dlPtr->nextPtr = lowestPtr;
        lowestPtr = dlPtr;
        TkTextIndexForwChars(&index, dlPtr->count, &index);
        charsToCount -= dlPtr->count;
    } while ((charsToCount > 0) && (index.linePtr == dlPtr->index.linePtr));

    /*
     * Scan through the display lines to see if we've covered enough
     * vertical distance.  If so, save the starting index for the
     * line at the desired location.
     */

    for (dlPtr = lowestPtr; dlPtr != NULL; dlPtr = dlPtr->nextPtr) {
        distance -= dlPtr->height;
        if (distance < 0) {
        *dstPtr = (noBestYet) ? dlPtr->index : bestIndex;
        break;
        }
        bestIndex = dlPtr->index;
        noBestYet = 0;
    }

    /*
     * Discard the display lines, then either return or prepare
     * for the next display line to lay out.
     */

    FreeDLines(textPtr, lowestPtr, (DLine *) NULL, 0);
    if (distance < 0) {
        return;
    }
    charsToCount = INT_MAX;        /* Consider all chars. in next line. */
    }

    /*
     * Ran off the beginning of the text.  Return the first character
     * in the text.
     */

    TkTextMakeIndex(textPtr->tree, 0, 0, dstPtr);
}

/*
 *--------------------------------------------------------------
 *
 * TkTextSeeCmd --
 *
 *    This procedure is invoked to process the "see" option for
 *    the widget command for text widgets. See the user documentation
 *    for details on what it does.
 *
 * Results:
 *    A standard Tcl result.
 *
 * Side effects:
 *    See the user documentation.
 *
 *--------------------------------------------------------------
 */

int
TkTextSeeCmd(textPtr, interp, argc, argv)
    TkText *textPtr;        /* Information about text widget. */
    Tcl_Interp *interp;        /* Current interpreter. */
    int argc;            /* Number of arguments. */
    char **argv;        /* Argument strings.  Someone else has already
                 * parsed this command enough to know that
                 * argv[1] is "see". */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    TkTextIndex index;
    int x, y, width, height, lineWidth, charCount, oneThird, delta;
    DLine *dlPtr;
    TkTextDispChunk *chunkPtr;

    if (argc != 3) {
    Tcl_AppendResult(interp, "wrong # args: should be \"",
        argv[0], " see index\"", (char *) NULL);
    return TCL_ERROR;
    }
    if (TkTextGetIndex(interp, textPtr, argv[2], &index) != TCL_OK) {
    return TCL_ERROR;
    }

    /*
     * If the specified position is the extra line at the end of the
     * text, round it back to the last real line.
     */

    if (TkBTreeLineIndex(index.linePtr) == TkBTreeNumLines(index.tree)) {
    TkTextIndexBackChars(&index, 1, &index);
    }

    /*
     * First get the desired position into the vertical range of the window.
     */

    TkTextSetYView(textPtr, &index, 1);

    /*
     * Now make sure that the character is in view horizontally.
     */

    if (dInfoPtr->flags & DINFO_OUT_OF_DATE) {
    UpdateDisplayInfo(textPtr);
    }
    lineWidth = dInfoPtr->maxX - dInfoPtr->x;
    if (dInfoPtr->maxLength < lineWidth) {
    return TCL_OK;
    }

    /*
     * Find the chunk that contains the desired index.
     */

    dlPtr = FindDLine(dInfoPtr->dLinePtr, &index);
    charCount = index.charIndex - dlPtr->index.charIndex;
    for (chunkPtr = dlPtr->chunkPtr; ; chunkPtr = chunkPtr->nextPtr) {
    if (charCount < chunkPtr->numChars) {
        break;
    }
    charCount -= chunkPtr->numChars;
    }

    /*
     * Call a chunk-specific procedure to find the horizontal range of
     * the character within the chunk.
     */

    (*chunkPtr->bboxProc)(chunkPtr, charCount, dlPtr->y + dlPtr->spaceAbove,
        dlPtr->height - dlPtr->spaceAbove - dlPtr->spaceBelow,
        dlPtr->baseline - dlPtr->spaceAbove, &x, &y, &width,
        &height);
    delta = x - dInfoPtr->curPixelOffset;
    oneThird = lineWidth/3;
    if (delta < 0) {
    if (delta < -oneThird) {
        dInfoPtr->newCharOffset = (x - lineWidth/2)/textPtr->charWidth;
    } else {
        dInfoPtr->newCharOffset -= ((-delta) + textPtr->charWidth - 1)
        / textPtr->charWidth;
    }
    } else {
    delta -= (lineWidth - width);
    if (delta > 0) {
        if (delta > oneThird) {
        dInfoPtr->newCharOffset = (x - lineWidth/2)/textPtr->charWidth;
        } else {
        dInfoPtr->newCharOffset += (delta + textPtr->charWidth - 1)
            / textPtr->charWidth;
        }
    } else {
        return TCL_OK;
    }
    }
    dInfoPtr->flags |= DINFO_OUT_OF_DATE;
    if (!(dInfoPtr->flags & REDRAW_PENDING)) {
    dInfoPtr->flags |= REDRAW_PENDING;
    Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
    }
    return TCL_OK;
}

/*
 *--------------------------------------------------------------
 *
 * TkTextXviewCmd --
 *
 *    This procedure is invoked to process the "xview" option for
 *    the widget command for text widgets. See the user documentation
 *    for details on what it does.
 *
 * Results:
 *    A standard Tcl result.
 *
 * Side effects:
 *    See the user documentation.
 *
 *--------------------------------------------------------------
 */

int
TkTextXviewCmd(textPtr, interp, argc, argv)
    TkText *textPtr;        /* Information about text widget. */
    Tcl_Interp *interp;        /* Current interpreter. */
    int argc;            /* Number of arguments. */
    char **argv;        /* Argument strings.  Someone else has already
                 * parsed this command enough to know that
                 * argv[1] is "xview". */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    int type, charsPerPage, count, newOffset;
    double fraction;

    if (dInfoPtr->flags & DINFO_OUT_OF_DATE) {
    UpdateDisplayInfo(textPtr);
    }

    if (argc == 2) {
    GetXView(interp, textPtr, 0);
    return TCL_OK;
    }

    newOffset = dInfoPtr->newCharOffset;
    type = Tk_GetScrollInfo(interp, argc, argv, &fraction, &count);
    switch (type) {
    case TK_SCROLL_ERROR:
        return TCL_ERROR;
    case TK_SCROLL_MOVETO:
        if (fraction > 1.0) {
        fraction = 1.0;
        }
        if (fraction < 0) {
        fraction = 0;
        }
        newOffset = (int) (((fraction * dInfoPtr->maxLength) / textPtr->charWidth)
            + 0.5);
        break;
    case TK_SCROLL_PAGES:
        charsPerPage = ((dInfoPtr->maxX - dInfoPtr->x) / textPtr->charWidth)
            - 2;
        if (charsPerPage < 1) {
        charsPerPage = 1;
        }
        newOffset += charsPerPage*count;
        break;
    case TK_SCROLL_UNITS:
        newOffset += count;
        break;
    }

    dInfoPtr->newCharOffset = newOffset;
    dInfoPtr->flags |= DINFO_OUT_OF_DATE;
    if (!(dInfoPtr->flags & REDRAW_PENDING)) {
    dInfoPtr->flags |= REDRAW_PENDING;
    Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ScrollByLines --
 *
 *    This procedure is called to scroll a text widget up or down
 *    by a given number of lines.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The view in textPtr's window changes to reflect the value
 *    of "offset".
 *
 *----------------------------------------------------------------------
 */

static void
ScrollByLines(textPtr, offset)
    TkText *textPtr;        /* Widget to scroll. */
    int offset;            /* Amount by which to scroll, in *screen*
                 * lines.  Positive means that information
                 * later in text becomes visible, negative
                 * means that information earlier in the
                 * text becomes visible. */
{
    int i, charsToCount, lineNum;
    TkTextIndex new, index;
    TkTextLine *lastLinePtr;
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    DLine *dlPtr, *lowestPtr;

    if (offset < 0) {
    /*
     * Must scroll up (to show earlier information in the text).
     * The code below is similar to that in MeasureUp, except that
     * it counts lines instead of pixels.
     */

    charsToCount = textPtr->topIndex.charIndex + 1;
    index.tree = textPtr->tree;
    offset--;            /* Skip line containing topIndex. */
    for (lineNum = TkBTreeLineIndex(textPtr->topIndex.linePtr);
        lineNum >= 0; lineNum--) {
        index.linePtr = TkBTreeFindLine(textPtr->tree, lineNum);
        index.charIndex = 0;
        lowestPtr = NULL;
        do {
        dlPtr = LayoutDLine(textPtr, &index);
        dlPtr->nextPtr = lowestPtr;
        lowestPtr = dlPtr;
        TkTextIndexForwChars(&index, dlPtr->count, &index);
        charsToCount -= dlPtr->count;
        } while ((charsToCount > 0)
            && (index.linePtr == dlPtr->index.linePtr));

        for (dlPtr = lowestPtr; dlPtr != NULL; dlPtr = dlPtr->nextPtr) {
        offset++;
        if (offset == 0) {
            textPtr->topIndex = dlPtr->index;
            break;
        }
        }

        /*
         * Discard the display lines, then either return or prepare
         * for the next display line to lay out.
         */

        FreeDLines(textPtr, lowestPtr, (DLine *) NULL, 0);
        if (offset >= 0) {
        goto scheduleUpdate;
        }
        charsToCount = INT_MAX;
    }

    /*
     * Ran off the beginning of the text.  Return the first character
     * in the text.
     */

    TkTextMakeIndex(textPtr->tree, 0, 0, &textPtr->topIndex);
    } else {
    /*
     * Scrolling down, to show later information in the text.
     * Just count lines from the current top of the window.
     */

    lastLinePtr = TkBTreeFindLine(textPtr->tree,
        TkBTreeNumLines(textPtr->tree));
    for (i = 0; i < offset; i++) {
        dlPtr = LayoutDLine(textPtr, &textPtr->topIndex);
        dlPtr->nextPtr = NULL;
        TkTextIndexForwChars(&textPtr->topIndex, dlPtr->count, &new);
        FreeDLines(textPtr, dlPtr, (DLine *) NULL, 0);
        if (new.linePtr == lastLinePtr) {
        break;
        }
        textPtr->topIndex = new;
    }
    }

    scheduleUpdate:
    if (!(dInfoPtr->flags & REDRAW_PENDING)) {
    Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
    }
    dInfoPtr->flags |= REDRAW_PENDING|DINFO_OUT_OF_DATE|REPICK_NEEDED;
}

/*
 *--------------------------------------------------------------
 *
 * TkTextYviewCmd --
 *
 *    This procedure is invoked to process the "yview" option for
 *    the widget command for text widgets. See the user documentation
 *    for details on what it does.
 *
 * Results:
 *    A standard Tcl result.
 *
 * Side effects:
 *    See the user documentation.
 *
 *--------------------------------------------------------------
 */

int
TkTextYviewCmd(textPtr, interp, argc, argv)
    TkText *textPtr;        /* Information about text widget. */
    Tcl_Interp *interp;        /* Current interpreter. */
    int argc;            /* Number of arguments. */
    char **argv;        /* Argument strings.  Someone else has already
                 * parsed this command enough to know that
                 * argv[1] is "yview". */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    int pickPlace, lineNum, type, charsInLine;
    Tk_FontMetrics fm;
    int pixels, count;
    size_t switchLength;
    double fraction;
    TkTextIndex index, new;
    TkTextLine *lastLinePtr;
    DLine *dlPtr;

    if (dInfoPtr->flags & DINFO_OUT_OF_DATE) {
    UpdateDisplayInfo(textPtr);
    }

    if (argc == 2) {
    GetYView(interp, textPtr, 0);
    return TCL_OK;
    }

    /*
     * Next, handle the old syntax: "pathName yview ?-pickplace? where"
     */

    pickPlace = 0;
    if (argv[2][0] == '-') {
    switchLength = strlen(argv[2]);
    if ((switchLength >= 2)
        && (strncmp(argv[2], "-pickplace", switchLength) == 0)) {
        pickPlace = 1;
        if (argc != 4) {
        Tcl_AppendResult(interp, "wrong # args: should be \"",
            argv[0], " yview -pickplace lineNum|index\"",
            (char *) NULL);
        return TCL_ERROR;
        }
    }
    }
    if ((argc == 3) || pickPlace) {
    if (Tcl_GetInt(interp, argv[2+pickPlace], &lineNum) == TCL_OK) {
        TkTextMakeIndex(textPtr->tree, lineNum, 0, &index);
        TkTextSetYView(textPtr, &index, 0);
        return TCL_OK;
    }

    /*
     * The argument must be a regular text index.
     */

    Tcl_ResetResult(interp);
    if (TkTextGetIndex(interp, textPtr, argv[2+pickPlace],
        &index) != TCL_OK) {
        return TCL_ERROR;
    }
    TkTextSetYView(textPtr, &index, pickPlace);
    return TCL_OK;
    }

    /*
     * New syntax: dispatch based on argv[2].
     */

    type = Tk_GetScrollInfo(interp, argc, argv, &fraction, &count);
    switch (type) {
    case TK_SCROLL_ERROR:
        return TCL_ERROR;
    case TK_SCROLL_MOVETO:
        if (fraction > 1.0) {
        fraction = 1.0;
        }
        if (fraction < 0) {
        fraction = 0;
        }
        fraction *= TkBTreeNumLines(textPtr->tree);
        lineNum = (int) fraction;
        TkTextMakeIndex(textPtr->tree, lineNum, 0, &index);
        charsInLine = TkBTreeCharsInLine(index.linePtr);
        index.charIndex = (int)((charsInLine * (fraction-lineNum)) + 0.5);
        if (index.charIndex >= charsInLine) {
        TkTextMakeIndex(textPtr->tree, lineNum+1, 0, &index);
        }
        TkTextSetYView(textPtr, &index, 0);
        break;
    case TK_SCROLL_PAGES:
        /*
         * Scroll up or down by screenfuls.  Actually, use the
         * window height minus two lines, so that there's some
         * overlap between adjacent pages.
         */

        Tk_GetFontMetrics(textPtr->tkfont, &fm);
        if (count < 0) {
        pixels = (dInfoPtr->maxY - 2*fm.linespace - dInfoPtr->y)*(-count)
            + fm.linespace;
        MeasureUp(textPtr, &textPtr->topIndex, pixels, &new);
        if (TkTextIndexCmp(&textPtr->topIndex, &new) == 0) {
            /*
             * A page of scrolling ended up being less than one line.
             * Scroll one line anyway.
             */

            count = -1;
            goto scrollByLines;
        }
        textPtr->topIndex = new;
        } else {
        /*
         * Scrolling down by pages.  Layout lines starting at the
         * top index and count through the desired vertical distance.
         */

        pixels = (dInfoPtr->maxY - 2*fm.linespace - dInfoPtr->y)*count;
        lastLinePtr = TkBTreeFindLine(textPtr->tree,
            TkBTreeNumLines(textPtr->tree));
        do {
            dlPtr = LayoutDLine(textPtr, &textPtr->topIndex);
            dlPtr->nextPtr = NULL;
            TkTextIndexForwChars(&textPtr->topIndex, dlPtr->count,
                &new);
            pixels -= dlPtr->height;
            FreeDLines(textPtr, dlPtr, (DLine *) NULL, 0);
            if (new.linePtr == lastLinePtr) {
            break;
            }
            textPtr->topIndex = new;
        } while (pixels > 0);
        }
        if (!(dInfoPtr->flags & REDRAW_PENDING)) {
        Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
        }
        dInfoPtr->flags |= REDRAW_PENDING|DINFO_OUT_OF_DATE|REPICK_NEEDED;
        break;
    case TK_SCROLL_UNITS:
        scrollByLines:
        ScrollByLines(textPtr, count);
        break;
    }
    return TCL_OK;
}

/*
 *--------------------------------------------------------------
 *
 * TkTextScanCmd --
 *
 *    This procedure is invoked to process the "scan" option for
 *    the widget command for text widgets. See the user documentation
 *    for details on what it does.
 *
 * Results:
 *    A standard Tcl result.
 *
 * Side effects:
 *    See the user documentation.
 *
 *--------------------------------------------------------------
 */

int
TkTextScanCmd(textPtr, interp, argc, argv)
    register TkText *textPtr;    /* Information about text widget. */
    Tcl_Interp *interp;        /* Current interpreter. */
    int argc;            /* Number of arguments. */
    char **argv;        /* Argument strings.  Someone else has already
                 * parsed this command enough to know that
                 * argv[1] is "scan". */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    TkTextIndex index;
    int c, x, y, totalScroll, newChar, maxChar;
    Tk_FontMetrics fm;
    size_t length;

    if (argc != 5) {
    Tcl_AppendResult(interp, "wrong # args: should be \"",
        argv[0], " scan mark|dragto x y\"", (char *) NULL);
    return TCL_ERROR;
    }
    if (Tcl_GetInt(interp, argv[3], &x) != TCL_OK) {
    return TCL_ERROR;
    }
    if (Tcl_GetInt(interp, argv[4], &y) != TCL_OK) {
    return TCL_ERROR;
    }
    c = argv[2][0];
    length = strlen(argv[2]);
    if ((c == 'd') && (strncmp(argv[2], "dragto", length) == 0)) {
    /*
     * Amplify the difference between the current position and the
     * mark position to compute how much the view should shift, then
     * update the mark position to correspond to the new view.  If we
     * run off the edge of the text, reset the mark point so that the
     * current position continues to correspond to the edge of the
     * window.  This means that the picture will start dragging as
     * soon as the mouse reverses direction (without this reset, might
     * have to slide mouse a long ways back before the picture starts
     * moving again).
     */

    newChar = dInfoPtr->scanMarkChar + (10*(dInfoPtr->scanMarkX - x))
        / (textPtr->charWidth);
    maxChar = 1 + (dInfoPtr->maxLength - (dInfoPtr->maxX - dInfoPtr->x)
        + textPtr->charWidth - 1)/textPtr->charWidth;
    if (newChar < 0) {
        dInfoPtr->scanMarkChar = newChar = 0;
        dInfoPtr->scanMarkX = x;
    } else if (newChar > maxChar) {
        dInfoPtr->scanMarkChar = newChar = maxChar;
        dInfoPtr->scanMarkX = x;
    }
    dInfoPtr->newCharOffset = newChar;

    Tk_GetFontMetrics(textPtr->tkfont, &fm);
    totalScroll = (10*(dInfoPtr->scanMarkY - y)) / fm.linespace;
    if (totalScroll != dInfoPtr->scanTotalScroll) {
        index = textPtr->topIndex;
        ScrollByLines(textPtr, totalScroll-dInfoPtr->scanTotalScroll);
        dInfoPtr->scanTotalScroll = totalScroll;
        if ((index.linePtr == textPtr->topIndex.linePtr) &&
            (index.charIndex == textPtr->topIndex.charIndex)) {
        dInfoPtr->scanTotalScroll = 0;
        dInfoPtr->scanMarkY = y;
        }
    }
    } else if ((c == 'm') && (strncmp(argv[2], "mark", length) == 0)) {
    dInfoPtr->scanMarkChar = dInfoPtr->newCharOffset;
    dInfoPtr->scanMarkX = x;
    dInfoPtr->scanTotalScroll = 0;
    dInfoPtr->scanMarkY = y;
    } else {
    Tcl_AppendResult(interp, "bad scan option \"", argv[2],
        "\": must be mark or dragto", (char *) NULL);
    return TCL_ERROR;
    }
    dInfoPtr->flags |= DINFO_OUT_OF_DATE;
    if (!(dInfoPtr->flags & REDRAW_PENDING)) {
    dInfoPtr->flags |= REDRAW_PENDING;
    Tcl_DoWhenIdle(DisplayText, (ClientData) textPtr);
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * GetXView --
 *
 *    This procedure computes the fractions that indicate what's
 *    visible in a text window and, optionally, evaluates a
 *    Tcl script to report them to the text's associated scrollbar.
 *
 * Results:
 *    If report is zero, then interp->result is filled in with
 *    two real numbers separated by a space, giving the position of
 *    the left and right edges of the window as fractions from 0 to
 *    1, where 0 means the left edge of the text and 1 means the right
 *    edge.  If report is non-zero, then interp->result isn't modified
 *    directly, but instead a script is evaluated in interp to report
 *    the new horizontal scroll position to the scrollbar (if the scroll
 *    position hasn't changed then no script is invoked).
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static void
GetXView(interp, textPtr, report)
    Tcl_Interp *interp;            /* If "report" is FALSE, string
                     * describing visible range gets
                     * stored in interp->result. */
    TkText *textPtr;            /* Information about text widget. */
    int report;                /* Non-zero means report info to
                     * scrollbar if it has changed. */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    char buffer[200];
    double first, last;
    int code;

    if (dInfoPtr->maxLength > 0) {
    first = ((double) dInfoPtr->curPixelOffset)
        / dInfoPtr->maxLength;
    last = first + ((double) (dInfoPtr->maxX - dInfoPtr->x))
        / dInfoPtr->maxLength;
    if (last > 1.0) {
        last = 1.0;
    }
    } else {
    first = 0;
    last = 1.0;
    }
    if (!report) {
    sprintf(interp->result, "%g %g", first, last);
    return;
    }
    if ((first == dInfoPtr->xScrollFirst) && (last == dInfoPtr->xScrollLast)) {
    return;
    }
    dInfoPtr->xScrollFirst = first;
    dInfoPtr->xScrollLast = last;
    sprintf(buffer, " %g %g", first, last);
    code = Tcl_VarEval(interp, textPtr->xScrollCmd,
        buffer, (char *) NULL);
    if (code != TCL_OK) {
    Tcl_AddErrorInfo(interp,
        "\n    (horizontal scrolling command executed by text)");
    Tcl_BackgroundError(interp);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * GetYView --
 *
 *    This procedure computes the fractions that indicate what's
 *    visible in a text window and, optionally, evaluates a
 *    Tcl script to report them to the text's associated scrollbar.
 *
 * Results:
 *    If report is zero, then interp->result is filled in with
 *    two real numbers separated by a space, giving the position of
 *    the top and bottom of the window as fractions from 0 to 1, where
 *    0 means the beginning of the text and 1 means the end.  If
 *    report is non-zero, then interp->result isn't modified directly,
 *    but a script is evaluated in interp to report the new scroll
 *    position to the scrollbar (if the scroll position hasn't changed
 *    then no script is invoked).
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static void
GetYView(interp, textPtr, report)
    Tcl_Interp *interp;            /* If "report" is FALSE, string
                     * describing visible range gets
                     * stored in interp->result. */
    TkText *textPtr;            /* Information about text widget. */
    int report;                /* Non-zero means report info to
                     * scrollbar if it has changed. */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    char buffer[200];
    double first, last;
    DLine *dlPtr;
    int totalLines, code, count;

    dlPtr = dInfoPtr->dLinePtr;
    totalLines = TkBTreeNumLines(textPtr->tree);
    first = ((double) TkBTreeLineIndex(dlPtr->index.linePtr))
        + ((double) dlPtr->index.charIndex)
        / (TkBTreeCharsInLine(dlPtr->index.linePtr));
    first /= totalLines;
    while (1) {
    if ((dlPtr->y + dlPtr->height) > dInfoPtr->maxY) {
        /*
         * The last line is only partially visible, so don't
         * count its characters in what's visible.
         */
        count = 0;
        break;
    }
    if (dlPtr->nextPtr == NULL) {
        count = dlPtr->count;
        break;
    }
    dlPtr = dlPtr->nextPtr;
    }
    last = ((double) TkBTreeLineIndex(dlPtr->index.linePtr))
        + ((double) (dlPtr->index.charIndex + count))
        / (TkBTreeCharsInLine(dlPtr->index.linePtr));
    last /= totalLines;
    if (!report) {
    sprintf(interp->result, "%g %g", first, last);
    return;
    }
    if ((first == dInfoPtr->yScrollFirst) && (last == dInfoPtr->yScrollLast)) {
    return;
    }
    dInfoPtr->yScrollFirst = first;
    dInfoPtr->yScrollLast = last;
    sprintf(buffer, " %g %g", first, last);
    code = Tcl_VarEval(interp, textPtr->yScrollCmd,
        buffer, (char *) NULL);
    if (code != TCL_OK) {
    Tcl_AddErrorInfo(interp,
        "\n    (vertical scrolling command executed by text)");
    Tcl_BackgroundError(interp);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * FindDLine --
 *
 *    This procedure is called to find the DLine corresponding to a
 *    given text index.
 *
 * Results:
 *    The return value is a pointer to the first DLine found in the
 *    list headed by dlPtr that displays information at or after the
 *    specified position.  If there is no such line in the list then
 *    NULL is returned.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static DLine *
FindDLine(dlPtr, indexPtr)
    register DLine *dlPtr;    /* Pointer to first in list of DLines
                 * to search. */
    TkTextIndex *indexPtr;    /* Index of desired character. */
{
    TkTextLine *linePtr;

    if (dlPtr == NULL) {
    return NULL;
    }
    if (TkBTreeLineIndex(indexPtr->linePtr)
        < TkBTreeLineIndex(dlPtr->index.linePtr)) {
    /*
     * The first display line is already past the desired line.
     */
    return dlPtr;
    }

    /*
     * Find the first display line that covers the desired text line.
     */

    linePtr = dlPtr->index.linePtr;
    while (linePtr != indexPtr->linePtr) {
    while (dlPtr->index.linePtr == linePtr) {
        dlPtr = dlPtr->nextPtr;
        if (dlPtr == NULL) {
        return NULL;
        }
    }
    linePtr = TkBTreeNextLine(linePtr);
    if (linePtr == NULL) {
        panic("FindDLine reached end of text");
    }
    }
    if (indexPtr->linePtr != dlPtr->index.linePtr) {
    return dlPtr;
    }

    /*
     * Now get to the right position within the text line.
     */

    while (indexPtr->charIndex >= (dlPtr->index.charIndex + dlPtr->count)) {
    dlPtr = dlPtr->nextPtr;
    if ((dlPtr == NULL) || (dlPtr->index.linePtr != indexPtr->linePtr)) {
        break;
    }
    }
    return dlPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * TkTextPixelIndex --
 *
 *    Given an (x,y) coordinate on the screen, find the location of
 *    the character closest to that location.
 *
 * Results:
 *    The index at *indexPtr is modified to refer to the character
 *    on the display that is closest to (x,y).
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
TkTextPixelIndex(textPtr, x, y, indexPtr)
    TkText *textPtr;        /* Widget record for text widget. */
    int x, y;            /* Pixel coordinates of point in widget's
                 * window. */
    TkTextIndex *indexPtr;    /* This index gets filled in with the
                 * index of the character nearest to (x,y). */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    register DLine *dlPtr;
    register TkTextDispChunk *chunkPtr;

    /*
     * Make sure that all of the layout information about what's
     * displayed where on the screen is up-to-date.
     */

    if (dInfoPtr->flags & DINFO_OUT_OF_DATE) {
    UpdateDisplayInfo(textPtr);
    }

    /*
     * If the coordinates are above the top of the window, then adjust
     * them to refer to the upper-right corner of the window.  If they're
     * off to one side or the other, then adjust to the closest side.
     */

    if (y < dInfoPtr->y) {
    y = dInfoPtr->y;
    x = dInfoPtr->x;
    }
    if (x >= dInfoPtr->maxX) {
    x = dInfoPtr->maxX - 1;
    }
    if (x < dInfoPtr->x) {
    x = dInfoPtr->x;
    }

    /*
     * Find the display line containing the desired y-coordinate.
     */

    for (dlPtr = dInfoPtr->dLinePtr; y >= (dlPtr->y + dlPtr->height);
        dlPtr = dlPtr->nextPtr) {
    if (dlPtr->nextPtr == NULL) {
        /*
         * Y-coordinate is off the bottom of the displayed text.
         * Use the last character on the last line.
         */

        x = dInfoPtr->maxX - 1;
        break;
    }
    }

    /*
     * Scan through the line's chunks to find the one that contains
     * the desired x-coordinate.  Before doing this, translate the
     * x-coordinate from the coordinate system of the window to the
     * coordinate system of the line (to take account of x-scrolling).
     */

    *indexPtr = dlPtr->index;
    x = x - dInfoPtr->x + dInfoPtr->curPixelOffset;
    for (chunkPtr = dlPtr->chunkPtr; x >= (chunkPtr->x + chunkPtr->width);
        indexPtr->charIndex += chunkPtr->numChars,
        chunkPtr = chunkPtr->nextPtr) {
    if (chunkPtr->nextPtr == NULL) {
        indexPtr->charIndex += chunkPtr->numChars - 1;
        return;
    }
    }

    /*
     * If the chunk has more than one character in it, ask it which
     * character is at the desired location.
     */

    if (chunkPtr->numChars > 1) {
    indexPtr->charIndex += (*chunkPtr->measureProc)(chunkPtr, x);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkTextCharBbox --
 *
 *    Given an index, find the bounding box of the screen area
 *    occupied by that character.
 *
 * Results:
 *    Zero is returned if the character is on the screen.  -1
 *    means the character isn't on the screen.  If the return value
 *    is 0, then the bounding box of the part of the character that's
 *    visible on the screen is returned to *xPtr, *yPtr, *widthPtr,
 *    and *heightPtr.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

int
TkTextCharBbox(textPtr, indexPtr, xPtr, yPtr, widthPtr, heightPtr)
    TkText *textPtr;        /* Widget record for text widget. */
    TkTextIndex *indexPtr;    /* Index of character whose bounding
                 * box is desired. */
    int *xPtr, *yPtr;        /* Filled with character's upper-left
                 * coordinate. */
    int *widthPtr, *heightPtr;    /* Filled in with character's dimensions. */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    DLine *dlPtr;
    register TkTextDispChunk *chunkPtr;
    int index;

    /*
     * Make sure that all of the screen layout information is up to date.
     */

    if (dInfoPtr->flags & DINFO_OUT_OF_DATE) {
    UpdateDisplayInfo(textPtr);
    }

    /*
     * Find the display line containing the desired index.
     */

    dlPtr = FindDLine(dInfoPtr->dLinePtr, indexPtr);
    if ((dlPtr == NULL) || (TkTextIndexCmp(&dlPtr->index, indexPtr) > 0)) {
    return -1;
    }

    /*
     * Find the chunk within the line that contains the desired
     * index.
     */

    index = indexPtr->charIndex - dlPtr->index.charIndex;
    for (chunkPtr = dlPtr->chunkPtr; ; chunkPtr = chunkPtr->nextPtr) {
    if (chunkPtr == NULL) {
        return -1;
    }
    if (index < chunkPtr->numChars) {
        break;
    }
    index -= chunkPtr->numChars;
    }

    /*
     * Call a chunk-specific procedure to find the horizontal range of
     * the character within the chunk, then fill in the vertical range.
     * The x-coordinate returned by bboxProc is a coordinate within a
     * line, not a coordinate on the screen.  Translate it to reflect
     * horizontal scrolling.
     */

    (*chunkPtr->bboxProc)(chunkPtr, index, dlPtr->y + dlPtr->spaceAbove,
        dlPtr->height - dlPtr->spaceAbove - dlPtr->spaceBelow,
        dlPtr->baseline - dlPtr->spaceAbove, xPtr, yPtr, widthPtr,
        heightPtr);
    *xPtr = *xPtr + dInfoPtr->x - dInfoPtr->curPixelOffset;
    if ((index == (chunkPtr->numChars-1)) && (chunkPtr->nextPtr == NULL)) {
    /*
     * Last character in display line.  Give it all the space up to
     * the line.
     */

    if (*xPtr > dInfoPtr->maxX) {
        *xPtr = dInfoPtr->maxX;
    }
    *widthPtr = dInfoPtr->maxX - *xPtr;
    }
    if ((*xPtr + *widthPtr) <= dInfoPtr->x) {
    return -1;
    }
    if ((*xPtr + *widthPtr) > dInfoPtr->maxX) {
    *widthPtr = dInfoPtr->maxX - *xPtr;
    if (*widthPtr <= 0) {
        return -1;
    }
    }
    if ((*yPtr + *heightPtr) > dInfoPtr->maxY) {
    *heightPtr = dInfoPtr->maxY - *yPtr;
    if (*heightPtr <= 0) {
        return -1;
    }
    }
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * TkTextDLineInfo --
 *
 *    Given an index, return information about the display line
 *    containing that character.
 *
 * Results:
 *    Zero is returned if the character is on the screen.  -1
 *    means the character isn't on the screen.  If the return value
 *    is 0, then information is returned in the variables pointed
 *    to by xPtr, yPtr, widthPtr, heightPtr, and basePtr.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

int
TkTextDLineInfo(textPtr, indexPtr, xPtr, yPtr, widthPtr, heightPtr, basePtr)
    TkText *textPtr;        /* Widget record for text widget. */
    TkTextIndex *indexPtr;    /* Index of character whose bounding
                 * box is desired. */
    int *xPtr, *yPtr;        /* Filled with line's upper-left
                 * coordinate. */
    int *widthPtr, *heightPtr;    /* Filled in with line's dimensions. */
    int *basePtr;        /* Filled in with the baseline position,
                 * measured as an offset down from *yPtr. */
{
    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
    DLine *dlPtr;

    /*
     * Make sure that all of the screen layout information is up to date.
     */

    if (dInfoPtr->flags & DINFO_OUT_OF_DATE) {
    UpdateDisplayInfo(textPtr);
    }

    /*
     * Find the display line containing the desired index.
     */

    dlPtr = FindDLine(dInfoPtr->dLinePtr, indexPtr);
    if ((dlPtr == NULL) || (TkTextIndexCmp(&dlPtr->index, indexPtr) > 0)) {
    return -1;
    }

    *xPtr = dInfoPtr->x - dInfoPtr->curPixelOffset + dlPtr->chunkPtr->x;
    *widthPtr = dlPtr->length - dlPtr->chunkPtr->x;
    *yPtr = dlPtr->y;
    if ((dlPtr->y + dlPtr->height) > dInfoPtr->maxY) {
    *heightPtr = dInfoPtr->maxY - dlPtr->y;
    } else {
    *heightPtr = dlPtr->height;
    }
    *basePtr = dlPtr->baseline;
    return 0;
}

/*
 *--------------------------------------------------------------
 *
 * TkTextCharLayoutProc --
 *
 *    This procedure is the "layoutProc" for character segments.
 *
 * Results:
 *    If there is something to display for the chunk then a
 *    non-zero value is returned and the fields of chunkPtr
 *    will be filled in (see the declaration of TkTextDispChunk
 *    in tkText.h for details).  If zero is returned it means
 *    that no characters from this chunk fit in the window.
 *    If -1 is returned it means that this segment just doesn't
 *    need to be displayed (never happens for text).
 *
 * Side effects:
 *    Memory is allocated to hold additional information about
 *    the chunk.
 *
 *--------------------------------------------------------------
 */

int
TkTextCharLayoutProc(textPtr, indexPtr, segPtr, offset, maxX, maxChars,
    noCharsYet, wrapMode, chunkPtr)
    TkText *textPtr;        /* Text widget being layed out. */
    TkTextIndex *indexPtr;    /* Index of first character to lay out
                 * (corresponds to segPtr and offset). */
    TkTextSegment *segPtr;    /* Segment being layed out. */
    int offset;            /* Offset within segment of first character
                 * to consider. */
    int maxX;            /* Chunk must not occupy pixels at this
                 * position or higher. */
    int maxChars;        /* Chunk must not include more than this
                 * many characters. */
    int noCharsYet;        /* Non-zero means no characters have been
                 * assigned to this display line yet. */
    Tk_Uid wrapMode;        /* How to handle line wrapping: tkTextCharUid,
                 * tkTextNoneUid, or tkTextWordUid. */
    register TkTextDispChunk *chunkPtr;
                /* Structure to fill in with information
                 * about this chunk.  The x field has already
                 * been set by the caller. */
{
    Tk_Font tkfont;
    int nextX, charsThatFit, count;
    CharInfo *ciPtr;
    char *p;
    TkTextSegment *nextPtr;
    Tk_FontMetrics fm;

    /*
     * Figure out how many characters will fit in the space we've got.
     * Include the next character, even though it won't fit completely,
     * if any of the following is true:
     *   (a) the chunk contains no characters and the display line contains
     *         no characters yet (i.e. the line isn't wide enough to hold
     *         even a single character).
     *   (b) at least one pixel of the character is visible, we haven't
     *         already exceeded the character limit, and the next character
     *         is a white space character.
     */

    p = segPtr->body.chars + offset;
    tkfont = chunkPtr->stylePtr->sValuePtr->tkfont;
    charsThatFit = MeasureChars(tkfont, p, maxChars, chunkPtr->x, maxX, 0,
        &nextX);
    if (charsThatFit < maxChars) {
    if ((charsThatFit == 0) && noCharsYet) {
        charsThatFit = 1;
        MeasureChars(tkfont, p, 1, chunkPtr->x, INT_MAX, 0, &nextX);
    }
    if ((nextX < maxX) && ((p[charsThatFit] == ' ')
        || (p[charsThatFit] == '\t'))) {
        /*
         * Space characters are funny, in that they are considered
         * to fit if there is at least one pixel of space left on the
         * line.  Just give the space character whatever space is left.
         */

        nextX = maxX;
        charsThatFit++;
    }
    if (p[charsThatFit] == '\n') {
        /*
         * A newline character takes up no space, so if the previous
         * character fits then so does the newline.
         */

        charsThatFit++;
    }
    if (charsThatFit == 0) {
        return 0;
    }
    }

    Tk_GetFontMetrics(tkfont, &fm);

    /*
     * Fill in the chunk structure and allocate and initialize a
     * CharInfo structure.  If the last character is a newline
     * then don't bother to display it.
     */

    chunkPtr->displayProc = CharDisplayProc;
    chunkPtr->undisplayProc = CharUndisplayProc;
    chunkPtr->measureProc = CharMeasureProc;
    chunkPtr->bboxProc = CharBboxProc;
    chunkPtr->numChars = charsThatFit;
    chunkPtr->minAscent = fm.ascent + chunkPtr->stylePtr->sValuePtr->offset;
    chunkPtr->minDescent = fm.descent - chunkPtr->stylePtr->sValuePtr->offset;
    chunkPtr->minHeight = 0;
    chunkPtr->width = nextX - chunkPtr->x;
    chunkPtr->breakIndex = -1;
    ciPtr = (CharInfo *) ckalloc((unsigned)
        (sizeof(CharInfo) - 3 + charsThatFit));
    chunkPtr->clientData = (ClientData) ciPtr;
    ciPtr->numChars = charsThatFit;
    strncpy(ciPtr->chars, p, (size_t) charsThatFit);
    if (p[charsThatFit-1] == '\n') {
    ciPtr->numChars--;
    }

    /*
     * Compute a break location.  If we're in word wrap mode, a
     * break can occur after any space character, or at the end of
     * the chunk if the next segment (ignoring those with zero size)
     * is not a character segment.
     */

    if (wrapMode != tkTextWordUid) {
    chunkPtr->breakIndex = chunkPtr->numChars;
    } else {
    for (count = charsThatFit, p += charsThatFit-1; count > 0;
        count--, p--) {
        if (isspace(UCHAR(*p))) {
        chunkPtr->breakIndex = count;
        break;
        }
    }
    if ((charsThatFit+offset) == segPtr->size) {
        for (nextPtr = segPtr->nextPtr; nextPtr != NULL;
            nextPtr = nextPtr->nextPtr) {
        if (nextPtr->size != 0) {
            if (nextPtr->typePtr != &tkTextCharType) {
            chunkPtr->breakIndex = chunkPtr->numChars;
            }
            break;
        }
        }
    }
    }
    return 1;
}

/*
 *--------------------------------------------------------------
 *
 * CharDisplayProc --
 *
 *    This procedure is called to display a character chunk on
 *    the screen or in an off-screen pixmap.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Graphics are drawn.
 *
 *--------------------------------------------------------------
 */

static void
CharDisplayProc(chunkPtr, x, y, height, baseline, display, dst, screenY)
    TkTextDispChunk *chunkPtr;        /* Chunk that is to be drawn. */
    int x;                /* X-position in dst at which to
                     * draw this chunk (may differ from
                     * the x-position in the chunk because
                     * of scrolling). */
    int y;                /* Y-position at which to draw this
                     * chunk in dst. */
    int height;                /* Total height of line. */
    int baseline;            /* Offset of baseline from y. */
    Display *display;            /* Display to use for drawing. */
    Drawable dst;            /* Pixmap or window in which to draw
                     * chunk. */
    int screenY;            /* Y-coordinate in text window that
                     * corresponds to y. */
{
    CharInfo *ciPtr = (CharInfo *) chunkPtr->clientData;
    TextStyle *stylePtr;
    StyleValues *sValuePtr;
    int offsetChars, offsetX;

    if ((x + chunkPtr->width) <= 0) {
    /*
     * The chunk is off-screen.
     */

    return;
    }

    stylePtr = chunkPtr->stylePtr;
    sValuePtr = stylePtr->sValuePtr;

    /*
     * If the text sticks out way to the left of the window, skip
     * over the characters that aren't in the visible part of the
     * window.  This is essential if x is very negative (such as
     * less than 32K);  otherwise overflow problems will occur
     * in servers that use 16-bit arithmetic, like X.
     */

    offsetX = x;
    offsetChars = 0;
    if (x < 0) {
    offsetChars = MeasureChars(sValuePtr->tkfont, ciPtr->chars,
        ciPtr->numChars, x, 0, x - chunkPtr->x, &offsetX);
    }

    /*
     * Draw the text, underline, and overstrike for this chunk.
     */

    if (ciPtr->numChars > offsetChars) {
    int numChars = ciPtr->numChars - offsetChars;
    char *string = ciPtr->chars + offsetChars;

    if ((numChars > 0) && (string[numChars - 1] == '\t')) {
        numChars--;
    }
    Tk_DrawChars(display, dst, stylePtr->fgGC, sValuePtr->tkfont, string,
        numChars, offsetX, y + baseline - sValuePtr->offset);
    if (sValuePtr->underline) {
        Tk_UnderlineChars(display, dst, stylePtr->fgGC, sValuePtr->tkfont,
            ciPtr->chars + offsetChars, offsetX,
            y + baseline - sValuePtr->offset,
            0, numChars);

    }
    if (sValuePtr->overstrike) {
        Tk_FontMetrics fm;

        Tk_GetFontMetrics(sValuePtr->tkfont, &fm);
        Tk_UnderlineChars(display, dst, stylePtr->fgGC, sValuePtr->tkfont,
            ciPtr->chars + offsetChars, offsetX,
            y + baseline - sValuePtr->offset
                - fm.descent - (fm.ascent * 3) / 10,
            0, numChars);
    }
    }
}

/*
 *--------------------------------------------------------------
 *
 * CharUndisplayProc --
 *
 *    This procedure is called when a character chunk is no
 *    longer going to be displayed.  It frees up resources
 *    that were allocated to display the chunk.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Memory and other resources get freed.
 *
 *--------------------------------------------------------------
 */

static void
CharUndisplayProc(textPtr, chunkPtr)
    TkText *textPtr;            /* Overall information about text
                     * widget. */
    TkTextDispChunk *chunkPtr;        /* Chunk that is about to be freed. */
{
    CharInfo *ciPtr = (CharInfo *) chunkPtr->clientData;

    ckfree((char *) ciPtr);
}

/*
 *--------------------------------------------------------------
 *
 * CharMeasureProc --
 *
 *    This procedure is called to determine which character in
 *    a character chunk lies over a given x-coordinate.
 *
 * Results:
 *    The return value is the index *within the chunk* of the
 *    character that covers the position given by "x".
 *
 * Side effects:
 *    None.
 *
 *--------------------------------------------------------------
 */

static int
CharMeasureProc(chunkPtr, x)
    TkTextDispChunk *chunkPtr;        /* Chunk containing desired coord. */
    int x;                /* X-coordinate, in same coordinate
                     * system as chunkPtr->x. */
{
    CharInfo *ciPtr = (CharInfo *) chunkPtr->clientData;
    int endX;

    return MeasureChars(chunkPtr->stylePtr->sValuePtr->tkfont, ciPtr->chars,
        chunkPtr->numChars-1, chunkPtr->x, x, 0, &endX);
}

/*
 *--------------------------------------------------------------
 *
 * CharBboxProc --
 *
 *    This procedure is called to compute the bounding box of
 *    the area occupied by a single character.
 *
 * Results:
 *    There is no return value.  *xPtr and *yPtr are filled in
 *    with the coordinates of the upper left corner of the
 *    character, and *widthPtr and *heightPtr are filled in with
 *    the dimensions of the character in pixels.  Note:  not all
 *    of the returned bbox is necessarily visible on the screen
 *    (the rightmost part might be off-screen to the right,
 *    and the bottommost part might be off-screen to the bottom).
 *
 * Side effects:
 *    None.
 *
 *--------------------------------------------------------------
 */

static void
CharBboxProc(chunkPtr, index, y, lineHeight, baseline, xPtr, yPtr,
    widthPtr, heightPtr)
    TkTextDispChunk *chunkPtr;        /* Chunk containing desired char. */
    int index;                /* Index of desired character within
                     * the chunk. */
    int y;                /* Topmost pixel in area allocated
                     * for this line. */
    int lineHeight;            /* Height of line, in pixels. */
    int baseline;            /* Location of line's baseline, in
                     * pixels measured down from y. */
    int *xPtr, *yPtr;            /* Gets filled in with coords of
                     * character's upper-left pixel.
                     * X-coord is in same coordinate
                     * system as chunkPtr->x. */
    int *widthPtr;            /* Gets filled in with width of
                     * character, in pixels. */
    int *heightPtr;            /* Gets filled in with height of
                     * character, in pixels. */
{
    CharInfo *ciPtr = (CharInfo *) chunkPtr->clientData;
    int maxX;

    maxX = chunkPtr->width + chunkPtr->x;
    MeasureChars(chunkPtr->stylePtr->sValuePtr->tkfont, ciPtr->chars, index,
        chunkPtr->x, 1000000, 0, xPtr);

    if (index == ciPtr->numChars) {
    /*
     * This situation only happens if the last character in a line
     * is a space character, in which case it absorbs all of the
     * extra space in the line (see TkTextCharLayoutProc).
     */

    *widthPtr = maxX - *xPtr;
    } else if ((ciPtr->chars[index] == '\t')
        && (index == (ciPtr->numChars-1))) {
    /*
     * The desired character is a tab character that terminates a
     * chunk;  give it all the space left in the chunk.
     */

    *widthPtr = maxX - *xPtr;
    } else {
    MeasureChars(chunkPtr->stylePtr->sValuePtr->tkfont,
        ciPtr->chars + index, 1, *xPtr, 1000000, 0, widthPtr);
    if (*widthPtr > maxX) {
        *widthPtr = maxX - *xPtr;
    } else {
        *widthPtr -= *xPtr;
    }
    }
    *yPtr = y + baseline - chunkPtr->minAscent;
    *heightPtr = chunkPtr->minAscent + chunkPtr->minDescent;
}

/*
 *----------------------------------------------------------------------
 *
 * AdjustForTab --
 *
 *    This procedure is called to move a series of chunks right
 *    in order to align them with a tab stop.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The width of chunkPtr gets adjusted so that it absorbs the
 *    extra space due to the tab.  The x locations in all the chunks
 *    after chunkPtr are adjusted rightward to align with the tab
 *    stop given by tabArrayPtr and index.
 *
 *----------------------------------------------------------------------
 */

static void
AdjustForTab(textPtr, tabArrayPtr, index, chunkPtr)
    TkText *textPtr;            /* Information about the text widget as
                     * a whole. */
    TkTextTabArray *tabArrayPtr;    /* Information about the tab stops
                     * that apply to this line.  May be
                     * NULL to indicate default tabbing
                     * (every 8 chars). */
    int index;                /* Index of current tab stop. */
    TkTextDispChunk *chunkPtr;        /* Chunk whose last character is
                     * the tab;  the following chunks
                     * contain information to be shifted
                     * right. */

{
    int x, desired, delta, width, decimal, i, gotDigit;
    TkTextDispChunk *chunkPtr2, *decimalChunkPtr;
    CharInfo *ciPtr;
    int tabX, prev, spaceWidth;
    char *p;
    TkTextTabAlign alignment;

    if (chunkPtr->nextPtr == NULL) {
    /*
     * Nothing after the actual tab;  just return.
     */

    return;
    }

    /*
     * If no tab information has been given, do the usual thing:
     * round up to the next boundary of 8 average-sized characters.
     */

    x = chunkPtr->nextPtr->x;
    if ((tabArrayPtr == NULL) || (tabArrayPtr->numTabs == 0)) {
    /*
     * No tab information has been given, so use the default
     * interpretation of tabs.
     */

    desired = NextTabStop(textPtr->tkfont, x, 0);
    goto update;
    }

    if (index < tabArrayPtr->numTabs) {
    alignment = tabArrayPtr->tabs[index].alignment;
    tabX = tabArrayPtr->tabs[index].location;
    } else {
    /*
     * Ran out of tab stops;  compute a tab position by extrapolating
     * from the last two tab positions.
     */

    if (tabArrayPtr->numTabs > 1) {
        prev = tabArrayPtr->tabs[tabArrayPtr->numTabs-2].location;
    } else {
        prev = 0;
    }
    alignment = tabArrayPtr->tabs[tabArrayPtr->numTabs-1].alignment;
    tabX = tabArrayPtr->tabs[tabArrayPtr->numTabs-1].location
        + (index + 1 - tabArrayPtr->numTabs)
        * (tabArrayPtr->tabs[tabArrayPtr->numTabs-1].location - prev);
    }

    if (alignment == LEFT) {
    desired = tabX;
    goto update;
    }

    if ((alignment == CENTER) || (alignment == RIGHT)) {
    /*
     * Compute the width of all the information in the tab group,
     * then use it to pick a desired location.
     */

    width = 0;
    for (chunkPtr2 = chunkPtr->nextPtr; chunkPtr2 != NULL;
        chunkPtr2 = chunkPtr2->nextPtr) {
        width += chunkPtr2->width;
    }
    if (alignment == CENTER) {
        desired = tabX - width/2;
    } else {
        desired = tabX - width;
    }
    goto update;
    }

    /*
     * Must be numeric alignment.  Search through the text to be
     * tabbed, looking for the last , or . before the first character
     * that isn't a number, comma, period, or sign.
     */

    decimalChunkPtr = NULL;
    decimal = gotDigit = 0;
    for (chunkPtr2 = chunkPtr->nextPtr; chunkPtr2 != NULL;
        chunkPtr2 = chunkPtr2->nextPtr) {
    if (chunkPtr2->displayProc != CharDisplayProc) {
        continue;
    }
    ciPtr = (CharInfo *) chunkPtr2->clientData;
    for (p = ciPtr->chars, i = 0; i < ciPtr->numChars; p++, i++) {
        if (isdigit(UCHAR(*p))) {
        gotDigit = 1;
        } else if ((*p == '.') || (*p == ',')) {
        decimal = p-ciPtr->chars;
        decimalChunkPtr = chunkPtr2;
        } else if (gotDigit) {
        if (decimalChunkPtr == NULL) {
            decimal = p-ciPtr->chars;
            decimalChunkPtr = chunkPtr2;
        }
        goto endOfNumber;
        }
    }
    }
    endOfNumber:
    if (decimalChunkPtr != NULL) {
    int curX;

    ciPtr = (CharInfo *) decimalChunkPtr->clientData;
    MeasureChars(decimalChunkPtr->stylePtr->sValuePtr->tkfont,
        ciPtr->chars, decimal, decimalChunkPtr->x, 1000000, 0, &curX);
    desired = tabX - (curX - x);
    goto update;
    } else {
    /*
     * There wasn't a decimal point.  Right justify the text.
     */

    width = 0;
    for (chunkPtr2 = chunkPtr->nextPtr; chunkPtr2 != NULL;
        chunkPtr2 = chunkPtr2->nextPtr) {
        width += chunkPtr2->width;
    }
    desired = tabX - width;
    }

    /*
     * Shift all of the chunks to the right so that the left edge is
     * at the desired location, then expand the chunk containing the
     * tab.  Be sure that the tab occupies at least the width of a
     * space character.
     */

    update:
    delta = desired - x;
    MeasureChars(textPtr->tkfont, " ", 1, 0, INT_MAX, 0, &spaceWidth);
    if (delta < spaceWidth) {
    delta = spaceWidth;
    }
    for (chunkPtr2 = chunkPtr->nextPtr; chunkPtr2 != NULL;
        chunkPtr2 = chunkPtr2->nextPtr) {
    chunkPtr2->x += delta;
    }
    chunkPtr->width += delta;
}

/*
 *----------------------------------------------------------------------
 *
 * SizeOfTab --
 *
 *    This returns an estimate of the amount of white space that will
 *    be consumed by a tab.
 *
 * Results:
 *    The return value is the minimum number of pixels that will
 *    be occupied by the index'th tab of tabArrayPtr, assuming that
 *    the current position on the line is x and the end of the
 *    line is maxX.  For numeric tabs, this is a conservative
 *    estimate.  The return value is always >= 0.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static int
SizeOfTab(textPtr, tabArrayPtr, index, x, maxX)
    TkText *textPtr;            /* Information about the text widget as
                     * a whole. */
    TkTextTabArray *tabArrayPtr;    /* Information about the tab stops
                     * that apply to this line.  NULL
                     * means use default tabbing (every
                     * 8 chars.) */
    int index;                /* Index of current tab stop. */
    int x;                /* Current x-location in line. Only
                     * used if tabArrayPtr == NULL. */
    int maxX;                /* X-location of pixel just past the
                     * right edge of the line. */
{
    int tabX, prev, result, spaceWidth;
    TkTextTabAlign alignment;

    if ((tabArrayPtr == NULL) || (tabArrayPtr->numTabs == 0)) {
    tabX = NextTabStop(textPtr->tkfont, x, 0);
    return tabX - x;
    }
    if (index < tabArrayPtr->numTabs) {
    tabX = tabArrayPtr->tabs[index].location;
    alignment = tabArrayPtr->tabs[index].alignment;
    } else {
    /*
     * Ran out of tab stops;  compute a tab position by extrapolating
     * from the last two tab positions.
     */

    if (tabArrayPtr->numTabs > 1) {
        prev = tabArrayPtr->tabs[tabArrayPtr->numTabs-2].location;
    } else {
        prev = 0;
    }
    tabX = tabArrayPtr->tabs[tabArrayPtr->numTabs-1].location
        + (index + 1 - tabArrayPtr->numTabs)
        * (tabArrayPtr->tabs[tabArrayPtr->numTabs-1].location - prev);
    alignment = tabArrayPtr->tabs[tabArrayPtr->numTabs-1].alignment;
    }
    if (alignment == CENTER) {
    /*
     * Be very careful in the arithmetic below, because maxX may
     * be the largest positive number:  watch out for integer
     * overflow.
     */

    if ((maxX-tabX) < (tabX - x)) {
        result = (maxX - x) - 2*(maxX - tabX);
    } else {
        result = 0;
    }
    goto done;
    }
    if (alignment == RIGHT) {
    result = 0;
    goto done;
    }

    /*
     * Note: this treats NUMERIC alignment the same as LEFT
     * alignment, which is somewhat conservative.  However, it's
     * pretty tricky at this point to figure out exactly where
     * the damn decimal point will be.
     */

    if (tabX > x) {
    result = tabX - x;
    } else {
    result = 0;
    }

    done:
    MeasureChars(textPtr->tkfont, " ", 1, 0, INT_MAX, 0, &spaceWidth);
    if (result < spaceWidth) {
    result = spaceWidth;
    }
    return result;
}

/*
 *---------------------------------------------------------------------------
 *
 * NextTabStop --
 *
 *    Given the current position, determine where the next default
 *    tab stop would be located.  This procedure is called when the
 *    current chunk in the text has no tabs defined and so the default
 *    tab spacing for the font should be used.
 *
 * Results:
 *    The location in pixels of the next tab stop.
 *
 * Side effects:
 *    None.
 *
 *---------------------------------------------------------------------------
 */

static int
NextTabStop(tkfont, x, tabOrigin)
    Tk_Font tkfont;        /* Font in which chunk that contains tab
                 * stop will be drawn. */
    int x;            /* X-position in pixels where last
                 * character was drawn.  The next tab stop
                 * occurs somewhere after this location. */
    int tabOrigin;        /* The origin for tab stops.  May be
                 * non-zero if text has been scrolled. */
{
    int tabWidth, rem;

    tabWidth = Tk_TextWidth(tkfont, "0", 1) * 8;
    if (tabWidth == 0) {
    tabWidth = 1;
    }

    x += tabWidth;
    rem = (x - tabOrigin) % tabWidth;
    if (rem < 0) {
    rem += tabWidth;
    }
    x -= rem;
    return x;
}

/*
 *---------------------------------------------------------------------------
 *
 *  MeasureChars --
 *
 *    Determine the number of characters from the string that will fit
 *    in the given horizontal span.  The measurement is done under the
 *    assumption that Tk_DisplayChars will be used to actually display
 *    the characters.
 *
 *    If tabs are encountered in the string, they will be expanded
 *    to the next tab stop, unless the TK_IGNORE_TABS flag is specified.
 *
 *    If a newline is encountered in the string, the line will be
 *    broken at that point, unless the TK_NEWSLINES_NOT_SPECIAL flag
 *    is specified.
 *
 * Results:
 *    The return value is the number of characters from source
 *    that fit in the span given by startX and maxX.  *nextXPtr
 *    is filled in with the x-coordinate at which the first
 *    character that didn't fit would be drawn, if it were to
 *    be drawn.
 *
 * Side effects:
 *    None.
 *
 *--------------------------------------------------------------
 */

static int
MeasureChars(tkfont, source, maxChars, startX, maxX, tabOrigin, nextXPtr)
    Tk_Font tkfont;        /* Font in which to draw characters. */
    CONST char *source;        /* Characters to be displayed.  Need not
                 * be NULL-terminated. */
    int maxChars;        /* Maximum # of characters to consider from
                 * source. */
    int startX;            /* X-position at which first character will
                 * be drawn. */
    int maxX;            /* Don't consider any character that would
                 * cross this x-position. */
    int tabOrigin;        /* X-location that serves as "origin" for
                 * tab stops. */
    int *nextXPtr;        /* Return x-position of terminating
                 * character here. */
{
    int curX, width, ch;
    CONST char *special, *end, *start;

    ch = 0;            /* lint. */
    curX = startX;
    special = source;
    end = source + maxChars;
    for (start = source; start < end; ) {
    if (start >= special) {
        /*
         * Find the next special character in the string.
         */

        for (special = start; special < end; special++) {
        ch = *special;
        if ((ch == '\t') || (ch == '\n')) {
            break;
        }
        }
    }

    /*
     * Special points at the next special character (or the end of the
     * string).  Process characters between start and special.
     */

    if (curX >= maxX) {
        break;
    }
    start += Tk_MeasureChars(tkfont, start, special - start, maxX - curX,
        0, &width);
    curX += width;
    if (start < special) {
        /*
         * No more chars fit in line.
         */

        break;
    }
    if (special < end) {
        if (ch == '\t') {
        start++;
        } else {
        break;
        }
    }
    }

    *nextXPtr = curX;
    return start - source;
}