objects/linedda.c

   1 /*
   2  * LineDDA
   3  *
   4  * Copyright 1993 Bob Amstadt
   5  *
   6 static char Copyright[] = "Copyright  Bob Amstadt, 1993";
   7 */
   8
   9 #include <stdlib.h>
  10 #include "windows.h"
  11 #include "callback.h"
  12
  13 /**********************************************************************
  14  *              LineDDA         (GDI.100)
  15  */
  16 void LineDDA(short nXStart, short nYStart, short nXEnd, short nYEnd,
  17              FARPROC callback, long lParam)
  18 {
  19     int xadd = 1, yadd = 1;
  20     int err,erradd;
  21     int cnt;
  22     int dx = nXEnd - nXStart;
  23     int dy = nYEnd - nYStart;
  24
  25     if (dx < 0)  {
  26       dx = -dx; xadd = -1;
  27     }
  28     if (dy < 0)  {
  29       dy = -dy; yadd = -1;
  30     }
  31     if (dx > dy) { /* line is "more horizontal" */
  32       err = 2*dy - dx; erradd = 2*dy - 2*dx;
  33       for(cnt = 0;cnt <= dx; cnt++) {
  34         CallLineDDAProc(callback,nXStart,nYStart,lParam);
  35         if (err > 0) {
  36           nYStart += yadd;
  37           err += erradd;
  38         } else  {
  39           err += 2*dy;
  40         }
  41         nXStart += xadd;
  42       }
  43     } else  { /* line is "more vertical" */
  44       err = 2*dx - dy; erradd = 2*dx - 2*dy;
  45       for(cnt = 0;cnt <= dy; cnt++) {
  46         CallLineDDAProc(callback,nXStart,nYStart,lParam);
  47         if (err > 0) {
  48           nXStart += xadd;
  49           err += erradd;
  50         } else  {
  51           err += 2*dx;
  52         }
  53         nYStart += yadd;
  54       }
  55     }
  56 }