Function push_card_clip 

pub fn push_card_clip(
    scene: &mut Scene,
    transform: Affine,
    rect: Rect,
    radius: f64,
)

Clip what is painted next to the inside of a card at rect with radius, until the caller’s scene.pop_layer(): content held past the card’s edge (a dragged marker, a scrolled drawing) is cut there instead of spilling over what surrounds the card.