objects/linedda.c

   1 /*
   2  * LineDDA
   3  *
   4  * Copyright 1993 Bob Amstadt
   5  *
   6  */
   7
   8 #include <stdlib.h>
   9 #include "windows.h"
  10 #include "callback.h"
  11
  12 /**********************************************************************
  13  *              LineDDA         (GDI.100)
  14  */
  15 void LineDDA(short nXStart, short nYStart, short nXEnd, short nYEnd,
  16              FARPROC16 callback, long lParam)
  17 {
  18     int xadd = 1, yadd = 1;
  19     int err,erradd;
  20     int cnt;
  21     int dx = nXEnd - nXStart;
  22     int dy = nYEnd - nYStart;
  23
  24     if (dx < 0)  {
  25       dx = -dx; xadd = -1;
  26     }
  27     if (dy < 0)  {
  28       dy = -dy; yadd = -1;
  29     }
  30     if (dx > dy) { /* line is "more horizontal" */
  31       err = 2*dy - dx; erradd = 2*dy - 2*dx;
  32       for(cnt = 0;cnt <= dx; cnt++) {
  33         CallLineDDAProc(callback,nXStart,nYStart,lParam);
  34         if (err > 0) {
  35           nYStart += yadd;
  36           err += erradd;
  37         } else  {
  38           err += 2*dy;
  39         }
  40         nXStart += xadd;
  41       }
  42     } else  { /* line is "more vertical" */
  43       err = 2*dx - dy; erradd = 2*dx - 2*dy;
  44       for(cnt = 0;cnt <= dy; cnt++) {
  45         CallLineDDAProc(callback,nXStart,nYStart,lParam);
  46         if (err > 0) {
  47           nXStart += xadd;
  48           err += erradd;
  49         } else  {
  50           err += 2*dx;
  51         }
  52         nYStart += yadd;
  53       }
  54     }
  55 }