Consistent winding order for polygon rings

[tschaub]

In order to support efficient rendering of holes in polygons (see #803), we store rings in consistent winding order: clockwise for exterior rings and counter-clockwise for interior rings.

Different formats call for different winding order in polygon rings. If we are consistent in our internal storage, then we can serialize consistently.

[tschaub]

Thanks for any review (@bartvde, you may be interested in this).

[ahocevar]

Looks great to me. Let's hope that ol.geom.LinearRing.isClockwise() is not too expensive, otherwise we might want to use it only for polygons that do have inner rings, which would add logic to the parsers. Anyway, please merge.

[elemoine]

I'll look at it.

[elemoine]

s/of/if ?

[elemoine]

I just noticed what I think is a typo. Otherwise looks good to me.

[ahocevar]

I'm also looking at this again right now. It seems to me that we could wrap

var coordinates = [];
coordinates.push(...);
var geom = new ol.geom.Polygon([coordinates]);

in a ring start - add - finalize workflow and calculate the edge value while building the ring. I'll send a pull request against @tschaub's clockwise branch to show what I mean.

[tschaub]

@ahocevar would you be opposed to having this merged and then issuing a separate pull request for the change you're envisioning?

There will be a number of places where the ring coordinates are assembled (when reading in parsers) and not all will be pushing individual vertex coordinates to a ring's coordinate array. I think it would make sense to consider your proposed change separate from this.

It would be great to allow the rendering work to proceed (see #803).

[ahocevar]

Sounds good @tschaub. Please merge (it seems to me I said something like this already above 😄).

[bartvde]

@tschaub can this FIXME be removed or is there still something TODO?

https://github.com/openlayers/ol3/blob/master/src/ol/format/geojsonformat.js#L1

[tschaub]

@tschaub can this FIXME be removed or is there still something TODO?

https://github.com/openlayers/ol3/blob/master/src/ol/format/geojsonformat.js#L1

See #3544.