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The C Users' Group Library 1994 August
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wc-cdrom-cusersgrouplibrary-1994-08.iso
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v_01_02
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1n02024a
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1990-07-09
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#include <math.h>
#include <stdio.h>
void swap( int *pa, int *pb);
#define MAX_X 3179
#define MAX_Y 1949
/******************************************************************
* lj_line - draw a line on the laser printer's internal page
*
* Parameters:
* x1 (in) - starting x coordinate in dots
* y1 (in) - starting y coordinate in dots
* x2 (in) - ending x coordinate in dots
* y2 (in) - ending y coordiante in dots
*
* Notes:
* If you may be varying the plotting dimensions (either by
* changing the output resolution or by changing the page
* orientation), make MAX_X and MAX_Y into global variables
* equal to the appropriate dimensions.
*
* Copyright:
* Original code by William H. Roetzheim (619) 669-6970
**********************************************************************/
void lj_line(int x1, int y1, int x2, int y2)
{
int d, dx, dy;
int Aincr, Bincr, xincr, yincr;
int x,y;
/* uses modified Bresenham's algorithm */
/* clip if line totally off plotting area */
if (((x1 < 0) && (x2 < 0)) ||
((y1 < 0) && (y2 < 0)) ||
((x1 > MAX_X) && (x2 > MAX_X)) ||
((y1 > MAX_Y) && (y2 > MAX_Y))) return;
/* test for vertical line */
if (x1 == x2)
{
if (y1 > y2) /* force y1 < y2 */
{
swap(&x1, &x2);
swap(&y1, &y2);
}
/* plot vertical line */
fprintf(stdprn, "\033*p%dx%dY", x1, y1); /* position to top of line */
fprintf(stdprn, "\033*c1a%dB", y2 - y1); /* width = 1, height = line height */
fprintf(stdprn, "\033*c0P"); /* print the line */
return;
}
/* test for horizontal line */
if (y1 == y2)
{
if (x1 > x2) /* force x1 < x2 */
{
swap (&x1, &x2);
swap (&y1, &y2);
}
/* plot horizontal line */
fprintf(stdprn, "\033*p%dx%dY", x1, y1); /* position to top of line */
fprintf(stdprn, "\033*c%da1B", x2 - x1); /* width = line, height = 1 */
fprintf(stdprn, "\033*c0P"); /* print the line */
return;
}
/* Here's where Bresenham's algorithm really starts */
if (abs(x2 - x1) > abs(y2 - y1))
{
if (x1 > x2) /* force x1 < x2 */
{
swap (&x1, &x2);
swap (&y1, &y2);
}
if (y2 > y1) yincr = 1;
else yincr = -1;
dx = x2 - x1;
dy = abs(y2 - y1);
d = 2 * dy - dx;
Aincr = 2 * (dy - dx);
Bincr = 2 * dy;
x = x1;
y = y1;
set_pixel(x, y);
for (x = x1 + 1; x <= x2; x++)
{
if (d >= 0)
{
y += yincr;
d += Aincr;
}
else d += Bincr;
set_pixel(x, y);
}
}
else
{
if (y1 > y2) /* force y1 < y2 */
{
swap (&x1, &x2);
swap (&y1, &y2);
}
if (x2 > x1) xincr = 1;
else xincr = -1;
dx = abs(x2 - x1);
dy = y2 - y1;
d = 2 * dx - dy;
Aincr = 2 * (dx - dy);
Bincr = 2 * dx;
x = x1;
y = y1;
set_pixel(x, y);
for (y = y1 + 1; y <= y2; y++)
{
if (d >= 0)
{
x += xincr;
d += Aincr;
}
else d += Bincr;
set_pixel(x, y);
}
}
}
void swap( int *pa, int *pb)
{
int t;
t = * pa;
*pa = *pb;
*pb = t;
}