#include <stdlib.h>
   #include <math.h>

   /*  Bresenham line-drawing procedure for |m| < 1.0.  */
   void lineBres (int x0, int y0, int xEnd, int yEnd)
   {
      int dx = fabs (xEnd - x0),  dy = fabs(yEnd - y0);
      int p = 2 * dy - dx;
      int twoDy = 2 * dy,  twoDyMinusDx = 2 * (dy - dx);
      int x, y;

      /* Determine which endpoint to use as start position.  */
      if (x0 > xEnd) {
         x = xEnd;
         y = yEnd;
         xEnd = x0;
      }
      else {
         x = x0;
         y = y0;
      }
      setPixel (x, y);

      while (x < xEnd) {
         x++;
         if (p < 0)
            p += twoDy;
         else {
            y++;
            p += twoDyMinusDx;
         }
         setPixel (x, y);
      }
   }