copy_alpha_rect (Imlib2::Image)

    /*
     * Copy the alpha channel from a rectangle of the source image to the
     * specified coordinates
     *
     * Examples:
     *   x, y, w, h = 10, 20, 100, 200
     *   dest_x, dest_y = 5, 10
     *   image.copy_alpha_rect source_image, x, y, w, h, dest_x, dest_y
     *
     *   source_rect = [10, 20, 100, 200]
     *   dest_coords = [5, 10]
     *   image.copy_alpha_rect source_image, source_rect, dest_coords
     *
     *   values = [10, 20, 100, 200, 5, 10]
     *   image.copy_alpha_rect source_image, values
     *
     */
    static VALUE image_copy_alpha_rect(int argc, VALUE *argv, VALUE self) {