image data from LPDIRECTDRAWSURFACE4

  

// Full object-to-object pixel-level collision detector:


short int Sprite_Collide(sprite_ptr object1, sprite_ptr object2) {
  
  int left1, left2, over_left;
  int right1, right2, over_right;
  int top1, top2, over_top;
  int bottom1, bottom2, over_bottom;
  int over_width, over_height;
  int i, j;
  unsigned char *pixel1, *pixel2;

  left1 = object1->x;
  left2 = object2->x;
  right1 = object1->x + object1->width;
  right2 = object2->x + object2->width;
  top1 = object1->y;
  top2 = object2->y;
  bottom1 = object1->y + object1->height;
  bottom2 = object2->y + object2->height;


  // Trivial rejections:


  if (bottom1 < top2) return(0);
  if (top1 > bottom2) return(0);
  
  if (right1 < left2) return(0);
  if (left1 > right2) return(0);


  // Ok, compute the rectangle of overlap:


  if (bottom1 > bottom2) over_bottom = bottom2;
  else over_bottom = bottom1;
 
  if (top1 < top2) over_top = top2;
  else over_top = top1;

  if (right1 > right2) over_right = right2;
  else over_right = right1;

  if (left1 < left2) over_left = left2;
  else over_left = left1;


  // Now compute starting offsets into both object's bitmaps:


  i = ((over_top - object1->y) * object1->width) + over_left;
  pixel1 = object1->frames[object1->curr_frame] + i;  
       //HERE I'D LIKE TO ACCESS AN LPDIRECTDRAWSURFACE4 SUFACE


  j = ((over_top - object2->y) * object2->width) + over_left;
  pixel2 = object2->frames[object2->curr_frame] + j;
      //HERE I'D LIKE TO ACCESS AN LPDIRECTDRAWSURFACE4 SUFACE

  
  // Now start scanning the whole rectangle of overlap, checking the 

  // corresponding pixel of each object's bitmap to see if they're both non-zero:


  for (i=0; i < over_height; i++) {
    for (j=0; j < over_width; j++) {
      if (*pixel1 > 0) && (*pixel2 > 0) return(1);
      pixel1++;
      pixel2++;
    };
    pixel1 += (object1->width - over_width);
    pixel2 += (object2->width - over_width);
  };


  // Worst case!  We scanned through the whole darn rectangle of overlap 

  // and couldn't find a single colliding pixel!


  return(0);

};