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The Presentation Manager Vector Fonts by Charles Petzold Let's begin with a question: What graphics programming language stores fonts as a lines and curves (rather than bitmaps), and thus allows fonts to be arbitrarily stretched, rotated, outlined, filled with different patterns, or even used as clipping areas? One answer is obviously PostScript, Adobe Systems' page composition language implemented on many high-end laser printers (beginning with the Apple LaserWriter) and Allied Corporation's Linotronic phototypesetters. Over the past few years, PostScript has become the language of choice for computer manipulation of fonts and text. But an equally valid answer is GPI -- the Graphics Programming Interface component of the OS/2 Presentation Manager. As we'll see, GPI has facilities to do virtually everything with fonts that you can do with PostScript. The Trouble With Text The display of text is always the most problematic part of a graphics programming system. Unlike lines and polygons (which are merely mathematical constructs), text is rooted in a long tradition of aesthetic typography. In any computer graphics system, the goal must always be to display text that is as pleasing and as easy to read as a well-printed book. Yet, most computer output devices (such as video displays and printers) are digital media. The subtly shaped and rounded characters that comprise traditional fonts must be broken down into discrete pixels for storage and then reassembled on the output device. This often causes distortions in the appearance of the text. But one major advantage of using a computer for this job is versatility: We can use a wide variety of fonts in various sizes and characteristics, and modify these fonts for display. The extent to which we can modify fonts is dependent on the way in which the fonts are stored in memory. Images and Vectors A font is generally stored in computer (or printer) memory in one of two very different ways: First, a font can be stored as an "image" or "bitmap." Each character of the font is simply a rectanglar array of bits. The 0 bits generally correspond to the background around the character and the 1 bits correspond to the character itself. Secondly, a font can be stored in a "vector" or "outline" format. Each character is defined as a series of lines and curves that enclose areas. The character is displayed by drawing the outline on the output device and filling the enclosed areas. Image and vector fonts have distinct advantages and disadvantages. Image font are always created for specific font sizes and specific device resolutions. The size of a particular image font cannot easily be changed. (For example, enlarging an image font by doubling the rows and columns of pixels often emphasizes the jaggedness of the characters.) Also, image fonts cannot be rotated except possibly by 90 degree increments. Vector fonts are much more malleable. Because they are defined as a series of lines and curves, vector fonts can be stretched or compressed to any size and can be rotated to any angle. Vector fonts are not tied to a particular output device resolution. In general, however, image fonts are more legible that vector fonts. Various techniques are used to design image fonts so they fool the eye into thinking the characters are smoother than they actually are. Vector fonts -- particularly when displayed on low resolution devices and scaled to small font sizes -- can be adjusted only by mathematical algorithms, which currently are less capable than human font designers. Another advantage of image fonts is performance: Vector fonts usually require much more processing time to draw each character. Most conventional laser printers store fonts as images, either within the printer or in font cartridges. The printer is restricted to specific font sizes and the characters cannot be arbitrarily rotated. Much more versatile are the fonts stored in PostScript-based printers. These fonts are stored as vectors. PostScript fonts can be stretched or compressed to any size, they can be arbitrarily rotated, filled with various patterns, and used for clipping. The GPI Fonts The Graphics Programming Interface (GPI) of the OS/2 Presentation Manager can, of course, take advantage of fonts that are stored in and supported by output devices such as laser printers. But GPI also includes its own support of both image and vector fonts. The image fonts are expected, of course, because they are particularly suited for low resolution video displays and dot matrix printers. Image fonts are an important part of most graphics programming systems (such as Microsoft Windows GDI). The addition of vector fonts in GPI is a real treat. GPI can use these vector fonts with any output device. Thus, various font techniques that previously have been restricted to PostScript printers are now possible with other laser printers and even the video display. This article shows you how to work with vector fonts in GPI and demonstrates many PostScript-like techniques. Quite simply, the font support in GPI is nearly as strong as that in PostScript. However, GPI has a serious deficiency that I'll discuss at the end of this article. OS/2 1.1 is shipped with three resource-only dyanamic link libraries with a .FON extension. These are font files, and the contents are shown in Figure 1. In addition, the video display device driver (DISPLAY.DLL) and printer device drivers may also contain fonts designed specifically for the device. For example, the default "System Proportional" font is stored in DISPLAY.DLL. Important: If you want to use any of the fonts in the .FON files, you must install the fonts from the Presentation Manager Control Panel program. It is only necessary to install one font from each of the three files, and you only need do this once. Each font has a face name. This is shown in quotation marks in Figure 1. Each of the image fonts is available in several point sizes and for several output devices: the CGA, EGA, VGA (and 8514/A), and IBM Proprinter. GPI can syntesize variations of these fonts, such as italic or boldfaced versions. Vector fonts, however, need not be designed for a particular output device and point size because they can be arbitrary scaled. You'll note that italic and boldface versions of the vector fonts are also included. The vector fonts in GPI are equivalent to the Courier, Helvetica, and Times fonts included in most PostScript printers. However, because Helvetica and Times are registered trademarks, these names are not used to identify the vector fonts in GPI. A little exploration of the font files will reveal that vector fonts are encoded as a series of GPI drawing orders. When drawing text with these fonts, GPI translates the drawing orders into GPI functions, usually GpiPolyLine to draw straight lines and GpiPolyFilletSharp to draw curves. The VECTFONT Program The VECTFONT program demonstrates the use GPI vector fonts. For purposes of clarity, I've divided the program into several modules. The VECTFONT "Display" menu lists 16 options. The first option (to display nothing) is the default. The other 15 options correspond to routines in the VF01.C through VF15.C files (described below). The VF00.C file contains some "helper" functions used by the routines in VF01.C through VF15.C. VECTFONT creates a micro presentation space during the WM_CREATE message using page units of PU_TWIPS. ("Twips" is fabricated word standing for "20th of a point." A printer's point size is 1/72nd inch, so page units correspond to 1/1440 inch.) VECTFONT then modifies the page viewport rectangle so that a page unit corresponds to 1 point, which (as you may know) is the default coordinate system in PostScript. Although VECTFONT displays output to the screen, vector fonts are obviously more suited for laser printers. As you will see, the appearance of the fonts -- even at 24 point sizes -- is not nearly as good as the image fonts. You'll also notice that several of the demonstration routines in VECTFONT requires a few seconds to run. For anything other than a demonstration program, you'd probably want to use a second thread of execution so as to not hold up message processing. Selecting an Outline Font To use an outline font in a Presentation Manager program, you must first create a "logical font" and then select the font into your presentation space. The GpiCreateLogFont function creates a logical font and associates the font with a local ID (a number between 1L and 254L that you select). This function requires a pointer to a structure of type FATTRS ("font attributes") that specifies the attributes of the font you want. To create a vector font, most of the fields in this structure can be set to zero. The most important fields are szFacename (which is set to the face name of the font) and fsFontUse, which is set to the constant identifiers FATTR_FONTUSE_OUTLINE and FATTR_FONTUSE_TRANSFORMABLE, combined with the C bitwise OR operator. You may prefer using the CreateVectorFont function in VF00.C for creating a vector font. The VF00.C file contains several other helpful functions that are used by the demonstration routines in VF01.C through VF15.C. The CreateVectorFont function requires only the presentation space handle, the local ID, and the face name: CreateVectorFont(hps, lcid, szFacename); After you create a logical font (using either GpiCreateLogFont or CreateVectorFont), you can select the font into the presentation space: GpiSetCharSet(hps, lcid); The lcid parameter is the local ID for the font. After the font is selected in the presentation space, you can alter the attributes of the font with various functions described below, obtain information about the font by calling GpiQueryFontMetrics, GpiQueryWidthTable, and GpiQueryTextBox, and you can use the font for text output with one of the text functions such as GpiCharStringAt. When you no longer need the font, you select the default font back into the presentation space: GpiSetCharSet( hps, LCID_DEFAULT); and then delete the local ID associated with the font: GpiDeleteSetId(hps, lcid); In VECTFONT, I always use the identifier LCID_MYFONT for the local ID. This is defined in VECTFONT.H as 1L. Scaling to a Point Size When you call GpiSetCharSet to select a vector font into the prsentation space, the initial width and height of the font are based on the GPI "character box," which defines a character width and height in page units. The default character box is based on the size of the default system font. You can change the character box size by calling GpiSetCharBox. Very important: To get a correctly proportioned vector font, it is necessary to change the character box size. Do not use the default Generally you set the height of the character box to the desired height of the font. If you want the a vector font to have a normal width, you set the width of the character box equal to the height. For a skinnier font, set the width of the character box less than the height; for a fatter font, set the width greater than the height. If you're working in page units of PU_PELS, you must also adjust the character box dimensions to account for differences in horizontal and vertical resolution of the output device. For this reason, it's much easier to work with vector fonts if you use one of the metric page units (PU_LOENGLISH, PU_HIENGLISH, PU_LOMETRIC, PU_HIMETRIC, or PU_TWIPS). With these page units, horizontal and vertical page units are the same. For example, suppose you're using page units of PU_TWIPS. This means that one page unit is equal to 1/20 of a point or 1/1440 inch. After selecting a vector font into the presentation space, you want to scale the font to 24 points. You first define a structure of type SIZEF: SIZEF sizfx; The two fields of this structure are named cx and cy and are interpreted as 32-bit FIXED numbers, that is, the high 16- bits are interpreted as an integer, and the low 16-bits are interpreted as a fraction. If you want to scale the vector font to a 24 point height, you can use the MAKEFIXED macro to set to the fields of the structure like this: sizfx.cx = MAKEFIXED( 24 * 20, 0); sizfx.cy = MAKEFIXED( 24 * 20, 0); Multiplying by 20 is necessary to convert the point size you want to twips. Then call GpiSetCharBox: GpiSetCharBox(hps, &sizfx); After setting the character box, any character or text dimensions you obtain from GpiQueryFontMetrics, GpiQueryTextBox, and GpiQueryWidthTable will reflect the new font size. The ScaleVectorFont routine in VF00.C can help in scaling a vector font to a desired point size. The function will work with any page units, even PU_PELS. The second and third parameters to ScaleVectorFont specify a point size in units of 0.1 points. (For example, use 240 for a 24-point size.) If you want a normally proportioned vector font, set the third parameter to ScaleVectorFont equal to the second parameter. The VF01.C file shows how the functions discussed so far can be used to display all the available vector fonts in 24 point sizes. You can run the function in VF01.C by selecting the "24 Point Fonts" option from the VECTFONT "Display" menu. Arbitrary Stretching Besides scaling the vector font to a specific point size, you can also scale vector fonts to fit within an arbitrary rectangle. For example, you may want to scale a short text string to fill the client window. The function shown in VF02.C shows how this is done. You can run this function by selecting "Stretched Font" from VECTFONT's menu. The function in VF02.C displays the word "Hello!" in the "Tms Rmn Italic" font stretched to the size of the client window. The ScaleFontToBox function in VF00.C helps out with this job. This function first calls GpiQueryTextBox to obtain the coordinates of a parallelogram that encompasses the text string. The character box is then scaled based on the size of this text box and the rectangle to which the font must be stretched. The QueryStartPointInTextBox function in VF00.C determines the starting point of the text string (that is, the point at the baseline of the left side of the first character) within this rectangle. This point is used in the GpiCharStringAt function to display the text. Mirror Images Besides scaling the font to a particular size, the character box can also flip the characters around the horizontal or vertical axis. If the character box height (the cy field of the SIZEF structure) is negative, then the characters will be flipped around the baseline and displayed upside down. If the character box width (the cx field) is negative, the individual characters are flipped around the vertical axis. Moreover, GpiCharStringAt will draw a character string from right to left. It's as if the whole character string is flipped around the vertical line at the left side of the first character. The function in VF03.C displays the same string four times, using all possible combinations of negative and positive character box dimensions. You can run this function by selecting "Mirrored Font" from the VECTFONT menu. Vector Fonts and Transformations Unlike image fonts, vector fonts can be scaled to any size and sheared and rotated to any angle. The matrix transforms described in my article "OS/2 Graphics Programming Interface: An Introduction to Coordinate Spaces" (Microsoft Systems Journal, Volume 3, Number 4) affect vector fonts in the same way they affect the display of other graphics primitives. In addition, GPI also supports several functions specifically for performing transforms on vector fonts. We've already seen how the GpiSetCharBox function allows font characters to be scaled. The GpiSetCharAngle rotates the font characters and the GpiSetCharShear performs x- shear. Character Angle and Rotation By default, the baseline of the vector font characters is parallel to the x axis in world coordinates. You can change this by calling GpiSetCharAngle. This rotates the vector fonts characters. The character angle is specified using a GRADIENTL structure, which has two fields named x and y of type LONG. Imagine a line connecting the point (0,0) to the point (x,y) in world coordinates. The baseline of each character is parallel to this line. The direction of the text is the same as the direction from (0,0) to (x,y). You can also think of this in trigonometric terms. The baseline of the text is parallel to a line at angle a measured counterclockwise from the x-axis, where: a = arctan (y/x) and y and x are the two fields of the GRADIENTL structure. The absolute magnitudes of y and x are not important. What's important are the relative magnitudes and signs. The signs of x and y determine the direction of the text string as indicated in the following table: x y Direction - - --------- + + To upper right - + To upper left - - To lower left + - To lower right The function in VF04.C uses the GpiSetCharAngle function to display eight text strings at 45 degree increments around the center of the client window. Each string displays the fields of the GRADIENTL structure that is used in the GpiSetCharAngle call. In this example, the text strings begin with a blank character so as not to make a mess of overlapping characters in the center of the client window. The character angle does not affect the interpretation of the starting position of the string specified in the GpiCharStringAt function. If you move your head so that a particular string is seen as running left to right, the starting position still refers to the point at the baseline of the left side of the first character. You can make the characters in a text string follow a curved path by individually calculating the starting position an angle of each character and displaying the characters one at a time. This is what is done in VF05.C to display "Hello, world!" around the perimeter of a circle. The text string is scaled based on the circumference of a circle that is positioned in the center of the window and has a diameter half the width or height (whichever is less) of the window. The GpiQueryWidthTable function is used to obtain the width of individual characters and then space them around the circle. Character Shear It is easy to confuse the character angle and character shear. Lets look at the difference. The character angle refers to the orientation of the baseline. Text displayed with various character angles is rotated but otherwise not distorted in any way. The character shear affects the appearance of the characters themselves apart from any rotation. Character shear by itself "bends" characters to the left or right, but the bottom of each character remains parallel to the x-axis. You can use character shear to create oblique (sometimes mistakenly called italic) versions of a font. To set character shear you call the GpiSetCharShear function. This function requires a pointer to a structure of type POINTL, which has two fields named x and y. Imagine a line drawn from (0,0) to the point (x,y) in world coordinates. The left and right sides of each character are parallel to this line. The function shown in in VF06.C displays seven text strings using different character shears. You can run this function by selecting "Character Shear" from the VECTFONT menu. Each string displays the x and y values used in the POINTL structure to set the character shear. The character shear is governed by the relative magnitudes and signs of the x and y fields of the POINTL structure. If the signs of both fields are the same, the characters tilt to the right; if different, the characters tilt to the left. The character shear does not cause characters to be flipped upside down. For example, character shear using the point (100,100) has the same effect as (-100,-100). The angle of the left and right sides of the characters from the y axis is sometimes called the shear angle. In theory, the shear angle can range to just above -180 degrees (infinite left shear) to just under +180 degrees (infinite right shear) and is equal to: a = arctan (x/y) where x and y are the two fields of the POINTL structure. When you set a non-default character shear, the GpiQueryTextBox function returns an array of points that define a parallelogram rather than a rectangle. However, the top and bottom sides of this text box are the same width as for a non-sheared text string, and the distance between the top and bottom sides also remains the same. You can use character shear to draw an oblique shadow of a text string. The function in VF07.C colors the background of the client window blue, and displays the text string "Shadow" twice. The first call to GpiCharStringAt displays the shadow. This is drawn in dark blue using a positive character shear. The second call to GpiCharStringAt draws the characters upright in red with a slightly smaller character box height. You can run this function by selecting "Font with Shadow" from the VECTFONT menu. A Primer on Paths To explore more capabilities of vector fonts, it's necessary to become familiar with the GPI "path," which is similar to a PostScript path. In GPI, you create a path by calling line drawing functions between calls to the GpiBeginPath and GpiEndPath functions: GpiBeginPath(hps, idPath); <... call line drawing functions ... > GpiEndPath (hps) ; This is called a "path bracket." In OS/2 1.1, idPath must be set equal to 1L. The functions that are valid within a path bracket are listed in the documentation of the Presentation Manager functions. The functions you call within the path bracket do not draw anything. Instead, the lines that make up the path are retained by the system. Often the lines you draw in a path will enclose areas, but they don't have to. After the GpiEndPath call, you can do one of three things with the path you've created: * Call GpiStrokePath to draw the lines that comprise the path. These lines are drawn using the geometric line width, joins, and ends (discussed shortly). * Call GpiFillPath to fill enclosed areas defined by the path. Any open areas are automatically closed. The area is filled with the current pattern. * Call GpiSetClipPath to make the enclosed areas of the path a clipping area. Any open areas are automatically closed. Subsequent GPI calls will only display output within the enclosed area defined by the path. Each of these three functions cause the path to be deleted. Prior to calling any of these three functions you can call GpiModifyPath, which I'll describe towards the end of this article. Normally, GpiCharStringAt and the other text output functions are not valid in a path bracket. The exception is when a vector font is selected in the presentation space. When called from within a path bracket, GpiCharStringAt does not draw the text string. Instead, the outlines of the characters become part of the path. This facility opens up a whole collection of PostScript-like stylistic techniques that you can use with vector fonts. Hollow Characters Let's begin by calling GpiCharStringAt in a path bracket and then use GpiStrokePath to draw the lines of the path. GpiStrokePath has the following syntax: GpiStrokePath( hps, idPath, 0L); In the initial version of the Presentation Manager, the last parameter of the function must be set to 0L. When used to stroke a path created by calling GpiCharStringAt, only the outline is drawn and not the interiors. This creates hollow characters. The function in VF08.C uses this technique to display the outline of the characters in the text string "Hollow." You can run this function by selecting "Hollow Font" from the VECTFONT menu. You may want to display characters in one color with an outline of another color. In this case, you must call GpiCharStringAt twice, first to draw the interior in a specific color, and secondly in a path bracket followed by a GpiStrokeFont call to draw the outline. The function in VF09.C does something like this to draw text with a drop shadow. The shadow is drawn first using a normal GpiCharStringAt call. Another GpiCharStringAt functions draws the text again in the current window background color at a 1/6 inch offset to the first string. This is surrounded by an outline created by a third GpiCharStringAt call in a path bracket followed by GpiStrokeFont. Quite similar to this is the creation of characters that look like solid blocks, as shown in the function in VF10.C. Eighteen character strings are drawn at 1 point offsets using CLR_DARKGREEN. This is capped by the character string drawn again in CLR_GREEN and the border in CLR_DARKGREEN. Geometrically Thick Lines At first, it may seem as if there is no difference between drawing a line normally, like this: GpiMove(hps, &ptlBeg); GpiLine(hps, &ptlEnd); and calling these same two functions within a path bracket and then stroking the path, like this: GpiBeginPath(hps, idPath); GpiMove(hps, &ptlBeg); GpiLine(hps, &ptlEnd); GpiEndPath(hps) GpiStrokePath(hps, idPath, 0); There are, in fact, some very significant differences. First, the line drawn with the normal GpiLine function has what is called a "cosmetic" line width. The default width of the line is based on the resolution of the output device. It is a device dependent width for a "normal" line. The width of the line does not change when you use matrix transforms to set different scaling factors in the coordinate space. Although GPI provides a function called GpiSetLineWidth to change the cosmetic line width, this function is not implemented in OS/2 1.1. But a line drawn by stroking a path has a "geometric" line width. This is a line width (in world coordinates) that you set with the GpiSetLineWidthGeom function. Because this line width is specified in world coordinates, it is affected by any scaling that you set using matrix transforms. Secondly, a line draw with GpiLine can have different line types that you set with the GpiSetLineType function. These line types are various combinations of dots and dashes. The line is drawn with the current line color and the current line mix. But a line drawn by stroking a path does not use the line type. The line is instead treated as an area that follows the path of the line but which has a geometric width. This area is filled with the pattern that you set with GpiSetPattern, colored with the current pattern foreground and background color, and the current pattern foreground and background mix. Third, a line drawn by stroking the path can have various types of line "joins" and "ends." By calling GpiSetLineJoin you can specify that lines meet with a rounded, square, or miter join. GpiSetLineEnd lets you specify rounded, square, or flat ends to the lines. The function in the VF11.C file demonstrates the use of geometrically thick lines filled with patterns to give the letters a kind of "neon" look. You can run this function by selecting "Neon Effect" from the VECTFONT menu. The function strokes the path using various geometric line widths filled with a PATSYM_HALFTONE pattern and several colors. The outline of the font is white, but surrounded with a halo of red. A better effect could be achieved on devices capable of more than 16 colors. In this case, you can use a solid pattern but color each stroke with a different shade of red. Filling the Path When introducing paths earlier in this article, I mentioned that you can do one of three things with a path: stroke it, fill it, or use it for clipping. Let's move on to the second: filling the path. To fill a path, you call: GpiFillPath(hps, idPath, lOption); This fills the path with the current pattern. Any open areas of the path are automatically closed before being filled. The lOption parameter can be either FPATH_ALTERNATE or FPATH_WINDING to fill the path using alternate or winding modes. For vector fonts, FPATH_WINDING causes the interiors of some letters (such as "O") to be filled. You'll probably want to use FPATH_ALTERNATE instead. If the current area filling pattern is PATSYM_SOLID, then the code: GpiBeginPath(hps, idPath); GpiCharStringAt(hps, &ptl, cch, szText); GpiEndPath(hps); GpiFillPath(hps, idPath, FPATH_ALTERNATE); does roughly the same thing with a vector font as a GpiCharStringAt by itself. When using GpiFillPath you'll want to set a pattern other than PATSYM_SOLID. (A bug in OS/2 1.1 causes the current pattern to be reset to PATSYM_SOLID during a path bracket in which GpiCharStringAt is called. You can get around this bug by calling GpiSetPattern after you end the path.) The function in VF12.C uses GpiFillPath to display the text string "Fade" eight times filled with the eight GPI shading patterns (PATSYM_DENSE1 through PATSYM_DENSE8) and then finishes by calling GpiCharStringAt outside of a path bracket. You can run this function by selecting "Fading Font" from the VECTFONT menu. Clipping to the Text Characters The third option after creating a path is to call GpiSetClipPath: GpiSetClipPath(hps, idPath, lOption); The lOption parameter can be either SCP_RESET (which equals 0L, so it's the default) or SCP_AND. The SCP_RESET option causes the clipping path to be reset so that no clipping occurs. The SCP_AND option sets the new clipping path to the intersection of the old clipping path and the path you've just defined in a path bracket. Any open areas in the path are automatically closed. You can combine the SCP_AND option with either SCP_ALTERNATE (the default) or SCP_WINDING. As with GpiFillPath, you'll probably want to use alternate mode when working with paths created from vector fonts The function in VF13.C calls GpiCharStringAt with the text string "WOW" within a path bracket. This is followed by a call to GpiSetClipPath. The clipping path is now the interior of the letters. The function draws a series of colored lines emanating from the center of the client window. The function in VF14.C uses a similar technique but draws a series of areas defined by splines. Modifying the Path Between the call to GpiEndPath to end the path and the call to GpiStrokePath, GpiFillPath, or GpiSetClipPath, you can call GpiModifyPath. This function uses the current geometric line width, line join, and line end to convert every line in the path to a new line that encloses an area around the old line. For example, suppose that the path contained a single straight line. After GpiModifyPath the path would contain a closed line in the shape of a hotdog. The width of this hotdog is the geometric line width. The ends of the hotdog could be round, square, or flat, depending on the current line end attribute. Following the creation of a path, these two functions in succession: GpiModifyPath(hps, ID_PATH, MPATH_STROKE); GpiFillPath(hps, ID_PATH, FPATH_WINDING) ; is usually equivalent to: GpiStrokePath(hps, ID_PATH, 0L); GpiModifyPath and GpiStrokePath are the only two functions that use the geometric line width, joins, and ends. In theory, you can call GpiStrokePath after GpiModifyPath, like this: GpiModifyPath(hps, ID_PATH, MPATH_STROKE); GpiStrokePath(hps, ID_PATH, 0L); This should do something, and it should be rather interesting, but GPI usually reports that it can't create the path because it's too complex. Instead, let's look at GpiModifyPath followed by GpiSetClipPath. The function in VF15.C is almost the same as the one in VF13.C except that it sets the geometric line width to 6 (1/12 inch) and calls GpiModifyPath before calling GpiSetClipPath. Note that the colored lines are clipped not to the interior of the characters, but to their original outlines. By the use of GpiModifyPath, the outlines of the characters have themselves been made into a path that is 1/12 inch wide. This is the path that is used for clipping. Is It Enough? I think it's clear that the facilities provided by GPI for working with vector fonts equal -- and sometimes exceed -- those in PostScript. The GPI interface is very powerful and very versatile. Is that enough? No, it's not. The implementation of vector fonts in GPI has a structural flaw that still leaves PostScript the king. Take a close look at the display of the "Helv" font. You'll notice that the two legs of the "H" are different in width by one pixel when they should be the same width. This is undoubtedly due to a rounding error. It's obviously more noticeable on a low-resolution video display than it would be on a 300 dpi laser printer, but even on a laser printer such errors will affect the legibility of the text. Errors such as this do not occur with PostScript fonts. PostScript fonts are true algorithms that are able to recognize and correct any anomalies in the rendition of the characters. In contrast, GPI fonts (which are encoded as a simple series of polylines and polyfillets) are drawn blindly without any feedback or correction. So, while we can rejoice in what we have in GPI, there is still the need to hope for improvement. Figure 1 Dynamic Link Library File Image Fonts Vector Fonts ------------ ----------- ------------ COURIER.FON "Courier" (8, 10, and "Courier" 12 points for CGA, "Courier Bold" EGA, VGA, and "Courier Italic" IBM Proprinter) "Courier Bold Italic" HELV.FON "Helv" (8, 10, 12, 14, "Helv" 18, and 24 points "Helv Bold" for CGA, EGA, VGA, "Helv Italic" and IBM Proprinter) "Helv Bold Italic" TIMES.FON "Tms Rmn" (8, 10, 12, "Tms Rmn" 14, 18, and 24 points "Tms Rmn Bold" for CGA, EGA, VGA, "Tms Rmn Italic" and IBM Proprinter) "Tms Rmn Bold Italic" Caption: The OS/2 1.1 dynamic link library files that Caption: contain fonts. The font face names are shown in quotation marks.