Function clip_mask

fn clip_mask<'a>(
    clip: &Clip,
    w: u32,
    h: u32,
    lt: f64,
    s: f32,
    centre: (f32, f32),
    cov: &'a mut Vec<u8>,
) -> Option<&'a [u8]>

Coverage for clip.mask over the whole canvas, or None when the clip has no enabled mask. The mask lives in canvas space around the layer’s placed centre (matching gpu.rs).