Function dash_path 

pub fn dash_path(path: &Path, dash: &Dash, tolerance: f32) -> Path

Cut path into the drawn pieces of dash.

tolerance is the flattening tolerance in the path’s own space, the same one the tessellator would use, so the dashes lie on the curve as closely as the curve itself is drawn.

An unusable pattern returns the path unchanged rather than nothing: a caller whose interval arithmetic produced a zero gets an undashed line, which is visibly wrong in a way that leads back to the pattern, where an empty result is invisible and leads nowhere.