/** Draw a (transparent) sprite at given coordinates with a given bounding box.

 * The bounding box extends from (x + bb_offset_x, y + bb_offset_y, z + bb_offset_z) to (x + w - 1, y + h - 1, z + dz - 1), both corners included.

 *

 * @note Bounding boxes are normally specified with bb_offset_x = bb_offset_y = bb_offset_z = 0. The extent of the bounding box in negative direction is

 *       defined by the sprite offset in the grf file.

 *       However if modifying the sprite offsets is not suitable (e.g. when using existing graphics), the bounding box can be tuned by bb_offset.

 *

 *

 * @param image the image to combine and draw,

 * @param pal the provided palette,

	ps->image = image;

	ps->pal = pal;

	ps->xmin = x + bb_offset_x;

	ps->ymin = y + bb_offset_y;

	ps->zmin = z + bb_offset_z;

	ps->comparison_done = false;

	ps->child = NULL;