Function rasterize 

pub fn rasterize(
    path: &BezPath,
    rule: FillRule,
    clip: IRect,
    scratch: &mut RasterScratch,
) -> TileCoverage

The coverage of path under rule within clip (device pixels, grown to whole tiles): per pixel, the average winding number over its area, mapped by the rule. Nonzero is min(|w|, 1); even-odd a triangle wave of period 2 in |w|. Only pixels where three or more windings cross within the pixel are approximate.