Do we need hull.js?

[adroitwhiz]

Currently, RenderWebGL._getConvexHullPointsForDrawable() calls hull from the hull.js library as its last step. However, I'm not entirely sure this is necessary-- it looks as though _getConvexHullPointsForDrawable already implements something like the monotone chain algorithm except sorted by y-coordinate (which is why we get "left" and "right" hulls).

The comment associated with _getConvexHullPointsForDrawable cryptically says the boundary points are passed to hull.js for "further work". What's hull.js actually doing here?

[adroitwhiz]

/cc @cwillisf

[linushp]

not need .
just 2D is enough