Bresenham_line_algorithm.c

/*Bresenham line algorithm: draw an line from (x1, y1) to (x2, y2) */
static void line(u_int *pic_buf, int x1, int y1, int x2, int y2)
{
    int dx = x2 - x1;
    int dy = y2 - y1;
    int inc;
    int pi;


    inc = ((dx * dy) >= 0) ? 1 : -1;
    if(abs(dx) > abs(dy)){
        if(dx < 0){
            swap(&x1, &x2);
            swap(&y1, &y2);
            dx = -dx;
            dy = -dy;
        }

        dy = (dy > 0) ? dy : -dy;
        pi = 2 * dy - dx;
        while(x1++ <= x2){
            draw_pixel(pic_buf, y1,  x1 - 1, y1, x1);
            if(pi < 0)
                pi += 2 * dy;
            else{
                y1 += inc;
                pi += 2 * (dy - dx);
            }
        }
     }else{
          if(dy < 0){
              swap(&x1, &x2);
              swap(&y1, &y2);
              dx = -dx;
              dy = -dy;
          }

          dx = (dx > 0)? dx : -dx;
          pi = 2 * dx - dy;
          while(y1++ < y2){
              draw_pixel(pic_buf,  y1 - 1, x1, y1 - 1, x1);
              if(pi < 0)
                  pi += 2 * dx;
              else{
                  x1 += inc;
                  pi += 2 *(dx - dy);
              }
          }
      }
}