Fix winding order for GeoJSON polygons before rendering

[mcwhittemore]

In mapbox-gl-draw we're seeing a problem where holes are rendered in polygons when we don't expect them to be. At first I thought that this was due to poor winding order management in gl-draw (which is true) but after talking to @sgillies about this a bit today I'm pretty sure mapbox-gl-js is implementing geojson holes incorrectly.

In the above image each new polygon is a its own feature. According to the spec holes happen when a second linear ring is provided to the array of linear ring coordinate arrays.

I'm guessing I can fix this in gl-draw by following the a linear ring SHOULD follow right-hand rule command, but still this should be fixed so end users don't get caught up in trying to check if their linear rights follow the right hand rule.

[jfirebaugh]

@mcwhittemore Can you post the GeoJSON that produces the depicted rendering?

cc @mourner

[averas]

I've noticed this too. Interestingly, it does not happen with the earcut-final branch if that could give any pointers..

[mcwhittemore]

@jfirebaugh here you go - https://gist.github.com/mcwhittemore/a4ee8d9559369d478729

[ansis]

We need to enforce winding order for geojson polygons internally. https://github.com/mapbox/geojson-rewind does this