222 lines
9.1 KiB
Markdown
222 lines
9.1 KiB
Markdown
------------------------ --------------------------------- --------------------
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[Previous](32-02.html) [Table of Contents](index.html) [Next](32-04.html)
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------------------------ --------------------------------- --------------------
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**LISTING 32.2 L32-2.C**
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* Sample program to illustrate VGA line drawing in 360x480
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* 256-color mode.
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*
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* Compiled with Borland C/C++.
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*
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* Must be linked with Listing 32.1 with a command line like:
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*
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* bcc l10-2.c l10-1.asm
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*
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* By Michael Abrash
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*/
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#include <dos.h> /* contains geninterrupt */
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#define TEXT_MODE 0x03
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#define BIOS_VIDEO_INT 0x10
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#define X_MAX 360 /* working screen width */
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#define Y_MAX 480 /* working screen height */
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extern void Draw360x480Dot();
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extern void Set360x480Mode();
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/*
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* Draws a line in octant 0 or 3 ( |DeltaX| >= DeltaY ).
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* |DeltaX|+1 points are drawn.
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*/
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void Octant0(X0, Y0, DeltaX, DeltaY, XDirection, Color)
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unsigned int X0, Y0; /* coordinates of start of the line */
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unsigned int DeltaX, DeltaY; /* length of the line */
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int XDirection; /* 1 if line is drawn left to right,
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-1 if drawn right to left */
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int Color; /* color in which to draw line */
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{
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int DeltaYx2;
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int DeltaYx2MinusDeltaXx2;
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int ErrorTerm;
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/* Set up initial error term and values used inside drawing loop */
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DeltaYx2 = DeltaY * 2;
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DeltaYx2MinusDeltaXx2 = DeltaYx2 - (int) ( DeltaX * 2 );
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ErrorTerm = DeltaYx2 - (int) DeltaX;
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/* Draw the line */
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Draw360x480Dot(X0, Y0, Color); /* draw the first pixel */
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while ( DeltaX-- ) {
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/* See if it’s time to advance the Y coordinate */
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if ( ErrorTerm >= 0 ) {
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/* Advance the Y coordinate & adjust the error term
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back down */
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Y0++;
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ErrorTerm += DeltaYx2MinusDeltaXx2;
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} else {
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/* Add to the error term */
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ErrorTerm += DeltaYx2;
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}
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X0 += XDirection; /* advance the X coordinate */
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Draw360x480Dot(X0, Y0, Color); /* draw a pixel */
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}
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}
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/*
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* Draws a line in octant 1 or 2 ( |DeltaX| < DeltaY ).
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* |DeltaY|+1 points are drawn.
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*/
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void Octant1(X0, Y0, DeltaX, DeltaY, XDirection, Color)
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unsigned int X0, Y0; /* coordinates of start of the line */
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unsigned int DeltaX, DeltaY; /* length of the line */
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int XDirection; /* 1 if line is drawn left to right,
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-1 if drawn right to left */
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int Color; /* color in which to draw line */
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{
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int DeltaXx2;
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int DeltaXx2MinusDeltaYx2;
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int ErrorTerm;
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/* Set up initial error term and values used inside drawing loop */
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DeltaXx2 = DeltaX * 2;
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DeltaXx2MinusDeltaYx2 = DeltaXx2 - (int) ( DeltaY * 2 );
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ErrorTerm = DeltaXx2 - (int) DeltaY;
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Draw360x480Dot(X0, Y0, Color);/* draw the first pixel */
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while ( DeltaY-- ) {
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/* See if it’s time to advance the X coordinate */
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if ( ErrorTerm >= 0 ) {
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/* Advance the X coordinate & adjust the error term
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back down */
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X0 += XDirection;
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ErrorTerm += DeltaXx2MinusDeltaYx2;
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} else {
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/* Add to the error term */
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ErrorTerm += DeltaXx2;
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}
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Y0++; /* advance the Y coordinate */
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Draw360x480Dot(X0, Y0,Color); /* draw a pixel */
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}
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}
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/*
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* Draws a line on the EGA or VGA.
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*/
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void EVGALine(X0, Y0, X1, Y1, Color)
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int X0, Y0; /* coordinates of one end of the line */
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int X1, Y1; /* coordinates of the other end of the line */
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unsigned char Color; /* color in which to draw line */
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{
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int DeltaX, DeltaY;
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int Temp;
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/* Save half the line-drawing cases by swapping Y0 with Y1
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and X0 with X1 if Y0 is greater than Y1. As a result, DeltaY
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is always > 0, and only the octant 0-3 cases need to be
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handled. */
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if ( Y0 > Y1 ) {
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Temp = Y0;
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Y0 = Y1;
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Y1 = Temp;
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Temp = X0;
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X0 = X1;
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X1 = Temp;
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}
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/* Handle as four separate cases, for the four octants in which
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Y1 is greater than Y0 */
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DeltaX = X1 - X0; /* calculate the length of the line
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in each coordinate */
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DeltaY = Y1 - Y0;
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if ( DeltaX > 0 ) {
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if ( DeltaX > DeltaY ) {
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Octant0(X0, Y0, DeltaX, DeltaY, 1, Color);
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} else {
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Octant1(X0, Y0, DeltaX, DeltaY, 1, Color);
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}
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} else {
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DeltaX = -DeltaX; /* absolute value of DeltaX */
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if ( DeltaX > DeltaY ) {
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Octant0(X0, Y0, DeltaX, DeltaY, -1, Color);
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} else {
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Octant1(X0, Y0, DeltaX, DeltaY, -1, Color);
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}
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}
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}
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/*
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* Subroutine to draw a rectangle full of vectors, of the
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* specified length and in varying colors, around the
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* specified rectangle center.
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*/
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void VectorsUp(XCenter, YCenter, XLength, YLength)
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int XCenter, YCenter; /* center of rectangle to fill */
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int XLength, YLength; /* distance from center to edge
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of rectangle */
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{
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int WorkingX, WorkingY, Color = 1;
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/* Lines from center to top of rectangle */
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WorkingX = XCenter - XLength;
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WorkingY = YCenter - YLength;
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for ( ; WorkingX < ( XCenter + XLength ); WorkingX++ )
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EVGALine(XCenter, YCenter, WorkingX, WorkingY, Color++);
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/* Lines from center to right of rectangle */
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WorkingX = XCenter + XLength - 1;
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WorkingY = YCenter - YLength;
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for ( ; WorkingY < ( YCenter + YLength ); WorkingY++ )
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EVGALine(XCenter, YCenter, WorkingX, WorkingY, Color++);
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/* Lines from center to bottom of rectangle */
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WorkingX = XCenter + XLength - 1;
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WorkingY = YCenter + YLength - 1;
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for ( ; WorkingX >= ( XCenter - XLength ); WorkingX-- )
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EVGALine(XCenter, YCenter, WorkingX, WorkingY, Color++);
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/* Lines from center to left of rectangle */
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WorkingX = XCenter - XLength;
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WorkingY = YCenter + YLength - 1;
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for ( ; WorkingY >= ( YCenter - YLength ); WorkingY-- )
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EVGALine(XCenter, YCenter, WorkingX, WorkingY, Color++);
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}
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/*
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* Sample program to draw four rectangles full of lines.
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*/
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void main()
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{
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char temp;
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Set360x480Mode();
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/* Draw each of four rectangles full of vectors */
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VectorsUp(X_MAX / 4, Y_MAX / 4, X_MAX / 4, Y_MAX / 4, 1);
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VectorsUp(X_MAX * 3 / 4, Y_MAX / 4, X_MAX / 4, Y_MAX / 4, 2);
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VectorsUp(X_MAX / 4, Y_MAX * 3 / 4, X_MAX / 4, Y_MAX / 4, 3);
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VectorsUp(X_MAX * 3 / 4, Y_MAX * 3 / 4, X_MAX / 4, Y_MAX / 4, 4);
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/* Wait for the enter key to be pressed */
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scanf(“%c”, &temp);
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/* Back to text mode */
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_AX = TEXT_MODE;
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geninterrupt(BIOS_VIDEO_INT);
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}
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The first thing you’ll notice when you run this code is that the speed
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of 360x480 256-color mode is pretty good, especially considering that
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most of the program is im-plemented in C.
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------------------- ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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 *Drawing in 360x480 256-color mode can sometimes actually be faster than in the 16-color modes, because the byte-per-pixel display memory organization of 256-color mode eliminates the need to read display memory before writing to it in order to isolate individual pixels coexisting within a single byte. In addition, 360x480 256-color mode is a variant of Mode X, which we’ll encounter in detail in Chapter 47, and supports all the high-performance features of Mode X.*
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------------------- ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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------------------------ --------------------------------- --------------------
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[Previous](32-02.html) [Table of Contents](index.html) [Next](32-04.html)
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------------------------ --------------------------------- --------------------
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* * * * *
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Graphics Programming Black Book © 2001 Michael Abrash
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