Function culled_for_damage 

pub fn culled_for_damage(
    scene: &Scene,
    parts: Option<&SectionParts>,
    key: TargetKey,
    damage: &[Rect],
) -> Option<Scene>

What of scene, drawn with parts, repainting damage (target pixels) on the target key names takes: the scene without the parts that cannot reach the damage (crate::scene_parts::culled), or None when it takes all of it: no parts, every part reaching the damage, or a damage repainted as one whole frame ([repaints_alone]), which draws every pixel. The renderer works through every path it is given, wherever it lands, so a software GPU otherwise spends as long on a caret as on the whole page.