Function gdk_paintable_compute_concrete_size

pub unsafe extern "C" fn gdk_paintable_compute_concrete_size(
    paintable: *mut GdkPaintable,
    specified_width: c_double,
    specified_height: c_double,
    default_width: c_double,
    default_height: c_double,
    concrete_width: *mut c_double,
    concrete_height: *mut c_double,
)