Source file: /~heha/hs/dos/hp2xx_hs.zip/bresnham.c

/* Copyright (c) 1991 - 1994 Heinz W. Werntges.  All rights reserved. */

/** bresnham.c: Implementation of Bresenham's algorithm
 **
 ** 91/01/04  V 1.00  HWW  Due to pseudocode in D.F. Rogers (1986) McGraw Hill
 ** 91/10/15  V 1.01  HWW  ANSI_C
 **/

#define	TEST	0



#include <stdio.h>
#include "bresnham.h"


static	DevPt	p_act;
static	int	dx, dy, s1, s2, swapdir, err, i;


DevPt	*bresenham_init (DevPt *pp1, DevPt *pp2)
/**
 ** Init. generation of a straight line between *pp1 & *pp2
 **
 ** Returns pointer to internally generated actual point of line.
 ** Use this ptr for further reference! Example of use:
 **
 **	..
 **	#include <share/bresnham.h>
 **	...
 **	DevPt	p1, p2, *pp;
 **	...
 **	pp = bresenham_init (&p1, &p2);
 **	do {
 **		plot (pp);
 **	} while (bresenham_next() != BRESENHAM_ERR);
 **/
{
  p_act = *pp1;

  if ((dx = pp2->x - pp1->x) != 0)
  {
	if (dx < 0)
	{
		dx = -dx;
		s1 = -1;
	}
	else
		s1 = 1;
  }
  else
	s1 = 0;	/* dx = abs(x2-x1), s1 = sign(x2-x1)	*/

  if ((dy = pp2->y - pp1->y) != 0)
  {
	if (dy < 0)
	{
		dy = -dy;
		s2 = -1;
	}
	else
		s2 = 1;
  }
  else
	s2 = 0;	/* dy = abs(y2-y1), s2 = sign(y2-y1)	*/

  if (dy > dx)
  {
	swapdir = dx;	/* use swapdir as temp. var.	*/
	dx = dy;
	dy = swapdir;
	swapdir = 1;
  }
  else
	swapdir = 0;

  i   = dx;		/* Init. of loop cnt	*/
  dy <<=1;
  err = dy - dx;	/* Init. of error term	*/
  dx <<=1;

  return &p_act;
}



int	bresenham_next (void)
/**
 ** Move actual point to next position (if possible)
 **
 ** Returns 0		 if ok,
 **	   BRESENHAM_EOL if last point reached (p_act == *pp2),
 **	   BRESENHAM_ERR else (e.g. if moving past EOL attempted)
 **/
{
  if (i<=0)
	return (BRESENHAM_ERR);	/* Beyond last point! */

  while (err >= 0)
  {
	if (swapdir)
		p_act.x += s1;
	else
		p_act.y += s2;
	err -=  dx;
  }
  if (swapdir)
	p_act.y += s2;
  else
	p_act.x += s1;
  err +=  dy;

  i--;	/* i==0 indicates "last point reached"	*/
  return ((i) ? 0 : BRESENHAM_EOL);
}



	/* Test module */
#if TEST
#ifdef __TURBOC__ && __MSDOS__


#include <graphics.h>


void	b_line (DevPt *pp1, DevPt *pp2, int col)
{
DevPt	*pp;

 pp = bresenham_init (pp1, pp2);
 do {
	putpixel (pp->x, pp->y, col);
 } while (bresenham_next() != BRESENHAM_ERR);
}


void	main(void)
{
int	gdriver=DETECT, gmode, MaxX, MaxY;
DevPt	pa, pc;

  initgraph (&gdriver, &gmode, "");

  MaxX = getmaxx();
  MaxY = getmaxy();

  pc.x = (MaxX + 1) >> 1;
  pc.y = (MaxY + 1) >> 1;

  for (pa.x=0, pa.y=0; pa.x < MaxX ; pa.x += 4)
	b_line (&pc, &pa, RED);
  for (pa.x=MaxX, pa.y=0; pa.y < MaxY ; pa.y += 3)
	b_line (&pc, &pa, GREEN);

  for (pa.x=MaxX, pa.y=MaxY; pa.x >= 0 ; pa.x -= 4)
	b_line (&pc, &pa, LIGHTRED);
  for (pa.x=0, pa.y=MaxY; pa.y >= 0 ; pa.y -= 3)
	b_line (&pc, &pa, LIGHTGREEN);

  getchar();
}

#endif
#endif