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HGRAPH.LIB V1.01 HGRAPH.LIB is a collection of subroutines to give Hercules graphics capability to MSC and QuickC and are better than MSC's & QuickC's in that they just have to be linked in. They do not require a driver to be loaded like with MSC & QC. This is version 1.01 release of these routines. They have been compiled and tested only on a Leading Edge Model "D" which has a hercules clone card in it. The only known difference between this clone card and a real Hercules card is that this clone fakes the light pen port (if you try to read its lightpen port for the graphics state it always returns text mode). INTRODUCTION The lib includes clearing and non-clearing subroutines to switch between text and graphics modes. A clear page and show page for clearing and switching between the two graphics pages. A pixel routine to read, write, and toggle a pixel. Two line subroutines one to draw a line in either white or black and one to toggle a line. And three string writing functions, one that treats the graphics screen as 43 rows and 90 columns while the other two let you define the upper left corner of where the string is to be written. There are also a save screen and a restore screen, similar to BASIC's BSAVE & BLOAD and a print screen routine for Epson printers. All the routines that write to the graphics screen are written in MSC MASM 5.1 for greater speed. The screen dump routines do their own buffering also for this reason. USAGE There is now a XHGRAPH.LIB library for each memory model, where X is the model (S, M, C, L). So you must link with the library of the same type model as the program was compiled with. The only restriction in using the libraries is that You must call hgraph_init() before using any of the other routines. i HGRAPH.LIB V1.01 The rest of the documentation is a list of library routines and what they do. The appendix holds a couple of examples and a few programing tips. The libraries are release into the public domain with the following restrictions: 1) That they only be transmitted from one person to the next in a complete and unmodified form. 2) That the libraries, documentation, and algorithms remain copy righted to me, Steven P. Murphy. 3) No warranties are expressed or implied. I am not responsible for the use, misuse, or abuse of these libraries. Any comments, suggestions, or bugs should be reported to: Steven P. Murphy 6581 Bing St. San Diego, CA 92115-6715 or murphys@cod.nosc.mil (USENET) And for those you who really like HGRAPH donations will not be refused. ii HGRAPH.LIB V1.01 All the routines treat the graphics screen as a grid of dots except hwrite and hstr which treat it as a set of rows and columns. For all the routines except hwrite and hstr the screen dimension are as follows: 0 719 0 ----------------------------------------------- | | | | | | | | | | | | | | | | | | | | | | | | 347 ----------------------------------------------- for hwrite and hstr the screen is: 0 89 0 ----------------------------------------------- | | | | | | | | | | | | | | | | | | | | | | | | 42 ----------------------------------------------- The conversion from rows & columns to dots is each row is eight dots height and each column is eight dots wide. iii HGRAPH.LIB V1.01 TABLE OF CONTENTS h_get_scrn . . . . . . . . . . . . . . . . . . 1 h_sav_scrn . . . . . . . . . . . . . . . . . . 2 hbox . . . . . . . . . . . . . . . . . . 3 hchar . . . . . . . . . . . . . . . . . . 4 hchar2 . . . . . . . . . . . . . . . . . . 5 hclearpg . . . . . . . . . . . . . . . . . . 6 hellipse . . . . . . . . . . . . . . . . . . 7 herc_there . . . . . . . . . . . . . . . . . . 8 hgmode . . . . . . . . . . . . . . . . . . 9 hgmode_nc . . . . . . . . . . . . . . . . . . 10 hgraph_init . . . . . . . . . . . . . . . . . . 11 hline . . . . . . . . . . . . . . . . . . 12 hpixel . . . . . . . . . . . . . . . . . . 13 hscdump . . . . . . . . . . . . . . . . . . 14 hscdump2 . . . . . . . . . . . . . . . . . . 15 hshowpg . . . . . . . . . . . . . . . . . . 16 hstr . . . . . . . . . . . . . . . . . . 17 htmode . . . . . . . . . . . . . . . . . . 18 htmode_nc . . . . . . . . . . . . . . . . . . 19 hwrite . . . . . . . . . . . . . . . . . . 20 hxchar . . . . . . . . . . . . . . . . . . 21 hxchar2 . . . . . . . . . . . . . . . . . . 22 hxline . . . . . . . . . . . . . . . . . . 23 hxstr . . . . . . . . . . . . . . . . . . 24 Appendix A . . . . . . . . . . . . . . . . . . 25 cornucopia.c . . . . . . . . . . . . . . . . 26 demo1.c . . . . . . . . . . . . . . . . 27 Appendix B . . . . . . . . . . . . . . . . . . 28 programing ideas . . . . . . . . . . . . . . 29 iv HGRAPH.LIB V1.01 H_GET_SCRN Summary #include <hgraph.h> Contains function prototypes int h_get_scrn(file_name); char *file_name /* name of file to get the */ /* image from */ Description Opens file_name for reading in binary mode and copies 32K bytes from file_name to graphics page 0 or 1 according to the current value of HGPAGE (see hgraph_init). Return Value H_get_scrn returns a -1 if it could not successfully open file_name other wise it will return a 0. See Also h_sav_scrn 1 HGRAPH.LIB V1.01 H_SAV_SCRN Summary #include <hgraph.h> Contains function prototypes int h_sav_scrn(file_name); char *file_name /* name of file to store */ /* image in */ Description Opens file_name for writing in binary mode and copies 32K bytes from graphics page 0 or 1 according to the current value of HGPAGE (see hgraph_init). Return Value H_sav_scrn returns a -1 if it could not successfully open file_name other wise it will return a 0. See Also h_get_scrn 2 HGRAPH.LIB V1.01 HBOX Summary #include <hgraph.h> Contains function prototypes void hbox(color, trow, lcol, brow, rcol); int color; /* should only be a 1 or 0 */ int trow; /* toprow 0 through 347 */ int lcol; /* left column 0 through 718 */ int brow; /* bottom row 1 through 348 */ int rcol; /* right column 1 through 719 */ Description Draws a box on page 0 or 1 according to the current value of HGPAGE (see hgraph_init). Hbox calls hline four time arranging the arguments each time so that a box is drawn where (trow, lcol) defines the upper left corner and (brow, rcol) is the lower right. Hbox does no bounds checking so bad ranges will produce weird results. Return Value There is no return value. See Also hline 3 HGRAPH.LIB V1.01 HCHAR Summary #include <hgraph.h> Contains function prototypes void hchar(x, y, string, attrib, count); int x; /* 0 through 719 */ int y; /* 0 through 347 */ char *string; /* ASCII 0 through 127 */ char attrib; /* HGNORM or HGINVS */ int count; /* number of chars in string */ Description Writes the upper left most corner of the string pointed to by string at the coordinates given after each character has been XORed with attrib. Hchar writes to the graphics page according to the current value of HGPAGE (see hgraph_init). There is no bounds checking done on x and y so numbers outside of range will give unknown results (probably not good). Hchar uses the IBM PC/XT/AT ROM character table. This table only has ASCII characters 0 through 127, values outside this range will give garbage. The attrib is xor with the character's bits on each scan line, values other than HGNORM (normal) and HGINVS (inverse) will just produce odd patterns. Count tells hchar how many of string's characters to plot. MSC regular run-time LIB has a functions strlen() and gcvt(), strlen() will produce a correct count and gcvt() will convert numbers to a string. Return Value There is no return value. See Also hchar2, hstr, hwrite, hxchar, hxchar2, hxstr MSC's or QuickC's strlen() and gcvt() 4 HGRAPH.LIB V1.01 HCHAR2 Summary #include <hgraph.h> Contains function prototypes void hchar2(x, y, string, attrib, count); int x; /* 0 through 719 */ int y; /* 0 through 347 */ char *string; /* ASCII 0 through 127 */ char attrib; /* HGNORM or HGINVS */ int count; /* number of chars in string */ Description Writes the upper left most corner of the string pointed to by string at the coordinates given after each character has been XORed with attrib. Hchar2 writes to the graphics page according to the current value of HGPAGE (see hgraph_init). There is no bounds checking done on x and y so numbers outside of range will give unknown results (probably not good). Hchar2's character table only has ASCII characters 0 through 127, values outside this range will give garbage. The attrib is xor with the character's bits on each scan line, values other than HGNORM (normal) and HGINVS (inverse) will just produce odd patterns. Count tells hchar2 how many of string's characters to plot. MSC regular run-time LIB has a functions strlen() and gcvt(), strlen() will produce a correct count and gcvt() will convert numbers to a string. Return Value There is no return value. See Also hchar, hstr, hwrite, hxchar, hxchar2, hxstr MSC's or QuickC's strlen() and gcvt() 5 HGRAPH.LIB V1.01 HCLEARPG Summary #include <hgraph.h> Contains function prototypes void hclearpg(void); Description Clears graphics page 0 or 1 according to the current value of HGPAGE (see hgraph_init). Return Value There is no return value. See Also hgmode, hgmode_nc 6 HGRAPH.LIB V1.01 HELLIPSE Summary #include <hgraph.h> Contains function prototypes void hellipse(color, x, y, r); Description Draws and ellipse on graphics page 0 or 1 according to the current value of HGPAGE (see hgraph_init) centered at (x, y) with a radius of r. the ellipse will have an aspect ratio of the current value of (int) HGRATIO. If the ratio is < 2 the major axis will be vertical, if it is > 2 the major axis will be horizontal, and if HGRATIO = 2 hellipse will produces the closes it can to a circle. no bounds checking is done if any part of the ellipse is off the screen weird things may happen. Return Value There is no return value See Also 7 HGRAPH.LIB V1.01 HERC_THERE Summary #include <hgraph.h> Contains function prototypes int herc_there(void); Description First it tests for a mono display adapter, if there is one it then watches port 3BA (hex) for a fixed time to see if bit 7 goes high. If bit 7 does go high it then pushes a 3 out port 3BF (hex) to turn on the second page of the herc card. Now it checks for memory in the second page. If this check is good it's a herc other wise it's just a funny mono card. Before it returns it pushes a 0 out port 3BF to return a herc card to diagonal mode. Return Value Herc_there returns a one if both of the above test are true and a zero if either is false. (I have tested this with my clone card, an EGA, a CGA, and a mono adapter, it worked correctly in all cases.) See Also 8 HGRAPH.LIB V1.01 HGMODE Summary #include <hgraph.h> Contains function prototypes void hgmode(void); Description Sets graphics mode, clears graphic pages 0 and 1 then switches to graphics page 0. Return Value There is no return value. See Also hgmode_nc 9 HGRAPH.LIB V1.01 HGMODE_NC Summary #include <hgraph.h> Contains function prototypes void hgmode_nc(void); Description Sets graphics mode, does not clears graphic pages 0 and 1 then switches to graphics page 0. Return Value There is no return value. See Also hgmode 10 HGRAPH.LIB V1.01 HGRAPH_INIT Summary #include <hgraph.h> Contains function prototypes void hgraph_init(void); Description Initializes the necessary global variables for HGRAPH.LIB. These variables are: int HGPAGE; /* current graphics page, used by all */ /* the library routines */ char HGATRB; /* character attribute for hwrite */ int HGRATIO; /* aspect ratio for hellipse */ The initial values for are HGPAGE = 1, HGATRB = 0x00, and HGRATIO = 2. HGPAGE should only be 1 or 0 if it is set to some value other than these two all the routine will default it to 1. HGATRB should only be HGNORM or HGINVS (defined in hgraph.h) other values will just cause the print to look funny. HGRATIO should be a positive int, 0 will cause it to draw a horizontal line, and a negative will hellipse to crash. Return Value There is no return value. See Also 11 HGRAPH.LIB V1.01 HLINE Summary #include <hgraph.h> Contains function prototypes void hline(function, x0, y0, x1, y1); int function; /* 0 - write pixels in black */ /* 1 - write pixels in white */ int x0; /* 0 through 719 */ int y0; /* 0 through 347 */ int x1; /* 0 through 719 */ int y1; /* 0 through 347 */ Description The default for function is 1, so if hline is called with function not equal to those listed you get function 1. The graphics page is set according to the current value of HGPAGE (see hgraph_init). There is no bounds checking done on x0, x1, y0, or y1 so numbers outside of range will give unknown results (probably not good). Return Value There is no return value. See Also hxline 12 HGRAPH.LIB V1.01 HPIXEL Summary #include <hgraph.h> Contains function prototypes void hpixel(function, x, y); int function; /* 0 - write pixel in black */ /* 1 - write pixel in white */ /* 2 - toggle pixel */ /* 3 - read pixel */ int x; /* 0 through 719 */ int y; /* 0 through 347 */ Description The default for function is 2, so if hpixel is called with function not equal to those listed you get function 2. The pixel is plotted on the graphics page according to the current value of HGPAGE (see hgraph_init). There is no bounds checking done on x and y so numbers outside of range will give unknown results (probably not good). Return Value The return value is the status the pixel was set to by any of the four functions. So hpixel while always return a 0 (for black) or a 1 (for white). See Also 13 HGRAPH.LIB V1.01 HSCDUMP Summary #include <hgraph.h> Contains function prototypes void hscdump(void); Description Dumps graphics page 0 or 1, according to the current value of HGPAGE (see hgraph_init), to an Epson or compatible printer. Each line is double struck to improve the clarity. Return Value There is no return value. See Also hscdump2 14 HGRAPH.LIB V1.01 HSCDUMP2 Summary #include <hgraph.h> Contains function prototypes void hscdump2(void); Description Dumps graphics page 0 or 1, according to the current value of HGPAGE (see hgraph_init), to an Epson or compatible printer. Each line is only single struck to improve the speed. Return Value There is no return value. See Also hscdump 15 HGRAPH.LIB V1.01 HSHOWPG Summary #include <hgraph.h> Contains function prototypes void hshowpg(void); Description Set graphics page 0 or 1, according to the current value of HGPAGE (see hgraph_init), to the currently displayed page. Return Value There is no return value. See Also hgmode, hgmode_nc 16 HGRAPH.LIB V1.01 HSTR Summary #include <hgraph.h> Contains function prototypes void hstr(column, row, string, attrib, count); int column; /* 0 through 89 */ int row; /* 0 through 42 */ char *string; /* pointer to the string */ char attrib; /* HGNORM or HGINVS */ int count; /* number of chars in string */ Description Writes the string pointed to by string at the row and column given after each character has been XORed with attrib. The graphics page written to is set according to the current value of HGPAGE (see hgraph_init). There is no bounds checking done on column and row so numbers outside of range will give unknown results (probably not good). Hstr's character table only has ASCII characters 0 through 127, values outside this range will give garbage. The attrib is xor with the character's bits on each scan line, values other than HGNORM (normal) and HGINVS (inverse) will just produce odd patterns. Count tells hstr how many of string's characters to plot. MSC regular run-time LIB has a functions strlen() and gcvt(), strlen() will produce a correct count and gcvt() will convert numbers to a string so they can be printed. Return Value There is no return value. See Also hchar, hchar2, hwrite, hxchar, hxchar2, hxstr MSC's or QuickC's strlen() and gcvt() Note: This is the fastest of hstr, hchar, and hchar2 for writing strings because it operates on byte boundaries. Only if you really need to write at a particular pixel location should hchar or hchar2 be used and of these two hchar2 is the better (only because its character table is internal, the same as hstr, so it is guaranteed to work on all machines). 17 HGRAPH.LIB V1.01 HTMODE Summary #include <hgraph.h> Contains function prototypes void htmode(void); Description Sets text mode, clears graphic pages 0 and 1 then switches to text page. Return Value There is no return value. See Also htmode_nc 18 HGRAPH.LIB V1.01 HTMODE_NC Summary #include <hgraph.h> Contains function prototypes void htmode_nc(void); Description Sets text mode, does not clears graphic pages 0 and 1 then switches to text page. Return Value There is no return value. See Also htmode 19 HGRAPH.LIB V1.01 HWRITE Summary #include <hgraph.h> Contains function prototypes int hwrite(row, col, string); int row; /* 0 through 42 */ int col; /* 0 through 89 */ char *string; /* pointer to the string */ Description Write string starting at (row, col) using the attribute value of HGATRB (see hgraph_init). The string is written to the graphics page set according to the current value of HGPAGE (see hgraph_init). Hwrite checks for bounds on both row and col, if the start of the string is not on the screen the string will not be written. If the string runs off the right edge it will just be truncated to avoid errors. MSC regular run- time LIB has a function gcvt() which will convert numbers to a string so they can be printed. Return Value Hwrite will return a 1 if it wrote any thing on the screen (truncated or not) or a 0 if (row, col) was off the screen (nothing written). See Also hchar, hchar2, hstr, hxchar, hxchar2, hxstr MSC's or QuickC's gcvt() 20 HGRAPH.LIB V1.01 HXCHAR Summary #include <hgraph.h> Contains function prototypes void hxchar(x, y, string, attrib, count); int x; /* 0 through 719 */ int y; /* 0 through 347 */ char *string; /* ASCII 0 through 127 */ char attrib; /* HGNORM or HGINVS */ int count; /* number of chars in string */ Description XORs string starting at the upper left most corner of the string pointed to by string at the coordinates given after each character has been XORed with attrib. Hxchar writes to the graphics page set by the current value of HGPAGE (see hgraph_init). There is no bounds checking done on x and y so numbers outside of range will give unknown results (probably not good). Hxchar uses the IBM PC/XT/AT ROM character table. This table only has ASCII characters 0 through 127, values outside this range will give garbage. The attrib is xor with the character's bits before it is xored to the screen, values other than HGNORM (normal) and HGINVS (inverse) for attrib will just produce odd patterns. Count tells hchar how many of string's characters to plot. MSC regular run-time LIB has a functions strlen() and gcvt(), strlen() will produce a correct count and gcvt() will convert numbers to a string. Return Value There is no return value. See Also hchar, hchar2, hstr, hwrite, hxchar2, hxstr MSC's or QuickC's strlen() and gcvt() 21 HGRAPH.LIB V1.01 HXCHAR2 Summary #include <hgraph.h> Contains function prototypes void hxchar2(x, y, string, attrib, count); int x; /* 0 through 719 */ int y; /* 0 through 347 */ char *string; /* ASCII 0 through 127 */ char attrib; /* HGNORM or HGINVS */ int count; /* number of chars in string */ Description XORs string starting at the upper left most corner of the string pointed to by string at the coordinates given after each character has been XORed with attrib. Hxchar2 writes to the graphics page according to the current value of HGPAGE (see hgraph_init). There is no bounds checking done on x and y so numbers outside of range will give unknown results (probably not good). Hxchar2's character table only has ASCII characters 0 through 127, values outside this range will give garbage. The attrib is xor with the character's bits before it is xored to the screen, values other than HGNORM (normal) and HGINVS (inverse) for attrib will just produce odd patterns. Count tells hxchar2 how many of string's characters to plot. MSC regular run- time LIB has a functions strlen() and gcvt(), strlen() will produce a correct count and gcvt() will convert numbers to a string. Return Value There is no return value. See Also hchar, hchar2, hstr, hwrite, hxchar, hxstr MSC's or QuickC's strlen() and gcvt() 22 HGRAPH.LIB V1.01 HXLINE Summary #include <hgraph.h> Contains function prototypes void hxline(x0, y0, x1, y1); int x0; /* 0 through 719 */ int y0; /* 0 through 347 */ int x1; /* 0 through 719 */ int y1; /* 0 through 347 */ Description Toggles the status of all the pixels along the given line. The graphics page is set according to the current value of HGPAGE (see hgraph_init). There is no bounds checking done on x0, x1, y0, or y1 so numbers outside of range will give unknown results (probably not good). Return Value There is no return value. See Also hline 23 HGRAPH.LIB V1.01 HXSTR Summary #include <hgraph.h> Contains function prototypes void hxstr(column, row, string, attrib, count); int column; /* 0 through 89 */ int row; /* 0 through 42 */ char *string; /* pointer to the string */ char attrib; /* HGNORM or HGINVS */ int count; /* number of chars in string */ Description XORs the string pointed to by string at the row and column given after each character has been XORed with attrib. The graphics page written to is set according to the current value of HGPAGE (see hgraph_init). There is no bounds checking done on column and row so numbers outside of range will give unknown results (probably not good). Hstr's character table only has ASCII characters 0 through 127, values outside this range will give garbage. The attrib is xor with the character's bits before it is xored to the screen, values other than HGNORM (normal) and HGINVS (inverse) will just produce odd patterns. Count tells hstr how many of string's characters to plot. MSC regular run- time LIB has a functions strlen() and gcvt(), strlen() will produce a correct count and gcvt() will convert numbers to a string so they can be printed. Return Value There is no return value. See Also hchar, hchar2, hstr, hwrite, hxchar, hxchar2 MSC's or QuickC's strlen() and gcvt() Note: This is the fastest of hxstr, hxchar, and hxchar2 for writing strings because it operates on byte boundaries. Only if you really need to write at a particular pixel location should hxchar or hxchar2 be used and of these two hxchar2 is the better (only because its character table is internal, the same as hxstr, so it is guaranteed to work on all machines). 24 HGRAPH.LIB V1.01 Appendix A (examples) 25 HGRAPH.LIB V1.01 /* CORNUCOPIA -- see article on "pseudo-hidden line removal" */ /* IBM-PC Exchange, May-June 1986 */ #include <math.h> #include <conio.h> #include <hgraph.h> main() { int d, a0, b0, a1, b1, a, b; double r, rada, radb; hgraph_init(); hgmode_nc(); hclearpg(); hshowpg(); hstr(40, 1, " CORNUCOPIA ", 0xff, 12); for (d = 1; d <= 100; ++d) { rada = (float)d; radb = 0.65 * rada; a0 = 20 + 4 * d; b0 = 20 + 2 * d + (int)(radb * 0.6 * sin(d/10.0)); hline(0, a0, b0, a1 = a0, b1 = b0 + (int)radb); for (r = 0.0; r < 6.3; r += 6.28/40.0) { a = a0 + (int)(rada * sin(r)); b = b0 + (int)(radb * cos(r)); hline(1, a1, b1, a, b); hline(0, a0, b0, a1 = a, b1 = b); } } /* This next section flips back and forth from * text to graphics three time to show the use of the * non-clearing hgmode_nc & htmode_nc the user must hit a * key to cause the flip */ hstr(10, 40, "Press any key to continue ... ", 0x00, 30); getch(); htmode_nc(); puts("Press any key to continue ... "); getch(); hgmode_nc(); hshowpg(); getch(); htmode_nc(); getch(); hgmode_nc(); hshowpg(); getch(); htmode(); /* this will clear the text screen */ } 26 HGRAPH.LIB V1.01 /* DEMO.C - a demo of hgraph.lib's string writing routines */ #include <string.h> #include <conio.h> #include <hgraph.h> char string[40] = "HGRAPH.LIB"; main() { int ct; char c; ct = strlen(string); hgraph_init(); hgmode_nc(); hclearpg(); hshowpg(); hstr(40, 1, string, HGINVS, ct); hstr(20, 10, "This is a demo of hstr, hchar, and hchar2", HGNORM, 41); hstr(10, 20, "This is a sample of hstr with normal attrib", HGNORM,43); hstr(10, 21, "This is a sample of hstr with inverse attrib", HGINVS,44); hchar(80, 200, "This is a sample of hchar with normal attrib", HGNORM,44); hchar(80, 209, "This is a sample of hchar with inverse attrib",HGINVS,45); hchar2(80, 240, "This is a sample of hchar2 with normal attrib",HGNORM,45); hchar2(80, 249, "This is a sample of hchar2 with inverse attrib",HGINVS,46); hstr(10, 40, "Press any key to continue ...", HGNORM, 29); getch(); htmode_nc(); } 27 HGRAPH.LIB V1.01 Appendix B (programing ideas) 28 HGRAPH.LIB V1.01 There are three ways to do screen swapping with these libraries to make it appear that you have a a full screen type window package. I will start with the easiest and work up to what I would consider the best. There is one thing to keep in mind, the text screen uses the same memory as the first half of graphics page 0. This fact must be consider when using hgmode_nc() and htmode_nc() because if you have written stuff to the text screen and then go to graphics page 0 there will be garbage on the top half of the monitor. The same is true if you do graphics on page 0 and switch to text with out clearing there will be trash all over the text screen. 1) If you do all your graphics on page 1 (the default) you could use C's standard functions (i.e printf, puts, ...) to write to the text screen (you don't have to leave graphics mode to do this). This way you could have graphics displayed and a help screen written to the text screen so if the user hit F1 you could call htmode_nc() and the help screen would appear, and then another key would call hgmode_nc() and the graphics would reappear. The only problem with this is a half to three quarters of a second delay built into both htmode_nc() and hgmode_nc() this will cause approximately a one second delay in switching form one screen to another. 2) There are two undocumented routines in hgraph.lib. void h_scrn_in( unsigned char *) void h_scrn_out( unsigned char *) where unsigned char * is a pointer to a buffer of at least 32768 bytes. The first, h_scrn_in reads the screen defined by HGPAGE and stores it into the buffer it was passed as an argument. The second, h_scrn_out copies the first 32767 bytes from the buffer it was passed as an argument to the screen defined by HGPAGE. So in the middle of doing graphics the user hits a key for help, the program would use h_scrn_in to save a copy of the current screen. Then it would call hclearpg followed by hwrite to display help messages. When the user wanted to switch back just call h_scrn_out and rewrite the image back. 29 HGRAPH.LIB V1.01 3) What I feel is the best is to use one graphics page for graphics and one graphics page for help. All that would have to be done is to reset HGPAGE and then call hshowpg to swap between the two. The code in the library to figure out which page and to set it is only ten lines in assembly. 30