filter (Imlib2::Image)

    /*
     * Apply a scripted filter or a static (eg Imlib2::Filter) filter
     *
     * Example:
     *   # apply a static filter
     *   filter = Imlib2::Filter.new 20
     *   filter.set 2, 2, Imlib2::Color::GREEN
     *   image.filter filter
     *
     *   # apply a scripted filter
     *   x, y = 20, 10
     *   filter_string = "tint( x=#{x}, y=#{y}, red=255, alpha=55 );"
     *   image.filter filter_string
     *
     */
    static VALUE image_filter(VALUE self, VALUE filter) {