Function rasterize 

pub fn rasterize(
    ops: &[PathOp],
    scale: f32,
    bin: (u8, u8),
    w: u32,
    h: u32,
    paint: MaskPaint,
) -> Vec<u8> 

Rasterizes ops (in logical px, relative to the node’s box) into a w × h alpha mask at scale, the node’s box shifted by bin quarter-pixels so a node at a fractional position lands on the pixel grid as it would be drawn. w * h bytes, row after row.