/*
* *** Listing 2 ***
*
* Sample program to illustrate VGA line drawing in 360x480
* 256-color mode.
*
* Compiled with Turbo C 2.0.
*
* Must be linked with Listing 1 with a command line like:
*
* tcc l2 l1.asm
*
* By Michael Abrash. 6/2/89.
*/
#include <dos.h> /* contains geninterrupt */
#define TEXT_MODE 0x03
#define BIOS_VIDEO_INT 0x10
#define X_MAX 360 /* working screen width */
#define Y_MAX 480 /* working screen height */
extern void Draw360x480Dot();
extern void Set360x480Mode();
/*
* Draws a line in octant 0 or 3 ( |DeltaX| >= DeltaY ).
* |DeltaX|+1 points are drawn.
*/
void Octant0(X0, Y0, DeltaX, DeltaY, XDirection, Color)
unsigned int X0, Y0; /* coordinates of start of the line */
unsigned int DeltaX, DeltaY; /* length of the line */
int XDirection; /* 1 if line is drawn left to right,
-1 if drawn right to left */
int Color; /* color in which to draw line */
{
int DeltaYx2;
int DeltaYx2MinusDeltaXx2;
int ErrorTerm;
/* Set up initial error term and values used inside drawing loop */
DeltaYx2 = DeltaY * 2;
DeltaYx2MinusDeltaXx2 = DeltaYx2 - (int) ( DeltaX * 2 );
ErrorTerm = DeltaYx2 - (int) DeltaX;
/* Draw the line */
Draw360x480Dot(X0, Y0, Color); /* draw the first pixel */
Read360x480Dot(X0, Y0); /* draw the first pixel */
while ( DeltaX-- ) {
/* See if it's time to advance the Y coordinate */
if ( ErrorTerm >= 0 ) {
/* Advance the Y coordinate & adjust the error term
back down */
Y0++;
ErrorTerm += DeltaYx2MinusDeltaXx2;
} else {
/* Add to the error term */
ErrorTerm += DeltaYx2;
}
X0 += XDirection; /* advance the X coordinate */
Draw360x480Dot(X0, Y0, Color); /* draw a pixel */
}
}
/*
* Draws a line in octant 1 or 2 ( |DeltaX| < DeltaY ).
* |DeltaY|+1 points are drawn.
*/
void Octant1(X0, Y0, DeltaX, DeltaY, XDirection, Color)
unsigned int X0, Y0; /* coordinates of start of the line */
unsigned int DeltaX, DeltaY; /* length of the line */
int XDirection; /* 1 if line is drawn left to right,
-1 if drawn right to left */
int Color; /* color in which to draw line */
{
int DeltaXx2;
int DeltaXx2MinusDeltaYx2;
int ErrorTerm;
/* Set up initial error term and values used inside drawing loop */
DeltaXx2 = DeltaX * 2;
DeltaXx2MinusDeltaYx2 = DeltaXx2 - (int) ( DeltaY * 2 );
ErrorTerm = DeltaXx2 - (int) DeltaY;
Draw360x480Dot(X0, Y0, Color); /* draw the first pixel */
Read360x480Dot(X0, Y0); /* draw the first pixel */
while ( DeltaY-- ) {
/* See if it's time to advance the X coordinate */
if ( ErrorTerm >= 0 ) {
/* Advance the X coordinate & adjust the error term
back down */
X0 += XDirection;
ErrorTerm += DeltaXx2MinusDeltaYx2;
} else {
/* Add to the error term */
ErrorTerm += DeltaXx2;
}
Y0++; /* advance the Y coordinate */
Draw360x480Dot(X0, Y0,Color); /* draw a pixel */
}
}
/*
* Draws a line on the EGA or VGA.
*/
void EVGALine(X0, Y0, X1, Y1, Color)
int X0, Y0; /* coordinates of one end of the line */
int X1, Y1; /* coordinates of the other end of the line */
unsigned char Color; /* color in which to draw line */
{
int DeltaX, DeltaY;
int Temp;
/* Save half the line-drawing cases by swapping Y0 with Y1
and X0 with X1 if Y0 is greater than Y1. As a result, DeltaY
is always > 0, and only the octant 0-3 cases need to be
handled. */
if ( Y0 > Y1 ) {
Temp = Y0;
Y0 = Y1;
Y1 = Temp;
Temp = X0;
X0 = X1;
X1 = Temp;
}
/* Handle as four separate cases, for the four octants in which
Y1 is greater than Y0 */
DeltaX = X1 - X0; /* calculate the length of the line
in each coordinate */
DeltaY = Y1 - Y0;
if ( DeltaX > 0 ) {
if ( DeltaX > DeltaY ) {
Octant0(X0, Y0, DeltaX, DeltaY, 1, Color);
} else {
Octant1(X0, Y0, DeltaX, DeltaY, 1, Color);
}
} else {
DeltaX = -DeltaX; /* absolute value of DeltaX */
if ( DeltaX > DeltaY ) {
Octant0(X0, Y0, DeltaX, DeltaY, -1, Color);
} else {
Octant1(X0, Y0, DeltaX, DeltaY, -1, Color);
}
}
}
/*
* Subroutine to draw a rectangle full of vectors, of the
* specified length and in varying colors, around the
* specified rectangle center.
*/
void VectorsUp(XCenter, YCenter, XLength, YLength)
int XCenter, YCenter; /* center of rectangle to fill */
int XLength, YLength; /* distance from center to edge
of rectangle */
{
int WorkingX, WorkingY, Color = 1;
/* Lines from center to top of rectangle */
WorkingX = XCenter - XLength;
WorkingY = YCenter - YLength;
for ( ; WorkingX < ( XCenter + XLength ); WorkingX++ )
EVGALine(XCenter, YCenter, WorkingX, WorkingY, Color++);
/* Lines from center to right of rectangle */
WorkingX = XCenter + XLength - 1;
WorkingY = YCenter - YLength;
for ( ; WorkingY < ( YCenter + YLength ); WorkingY++ )
EVGALine(XCenter, YCenter, WorkingX, WorkingY, Color++);
/* Lines from center to bottom of rectangle */
WorkingX = XCenter + XLength - 1;
WorkingY = YCenter + YLength - 1;
for ( ; WorkingX >= ( XCenter - XLength ); WorkingX-- )
EVGALine(XCenter, YCenter, WorkingX, WorkingY, Color++);
/* Lines from center to left of rectangle */
WorkingX = XCenter - XLength;
WorkingY = YCenter + YLength - 1;
for ( ; WorkingY >= ( YCenter - YLength ); WorkingY-- )
EVGALine(XCenter, YCenter, WorkingX, WorkingY, Color++);
}
/*
* Sample program to draw four rectangles full of lines.
*/
int main()
{
char temp;
Set360x480Mode();
/* Draw each of four rectangles full of vectors */
VectorsUp(X_MAX / 4, Y_MAX / 4, X_MAX / 4, Y_MAX / 4, 1);
VectorsUp(X_MAX * 3 / 4, Y_MAX / 4, X_MAX / 4, Y_MAX / 4, 2);
VectorsUp(X_MAX / 4, Y_MAX * 3 / 4, X_MAX / 4, Y_MAX / 4, 3);
VectorsUp(X_MAX * 3 / 4, Y_MAX * 3 / 4, X_MAX / 4, Y_MAX / 4, 4);
/* Wait for the enter key to be pressed */
scanf("%c", &temp);
/* Back to text mode */
_AX = TEXT_MODE;
geninterrupt(BIOS_VIDEO_INT);
}
