Incorrect intersection of MultiPolygon and Point

[LostDragonist]

maplibre-gl-js version: 5.2.0 (latest tested, bug goes back 9+ years)

browser: Chrome 133

Steps to Trigger Behavior

1. Create a MultiPolygon where an even number of Polygons appear the same location.
2. Attempt to use queryRenderedFeatures at that location to detect the MultiPolygon.
3. Observe you get no results.

Link to Demonstration

https://jsbin.com/bufawog/edit?html,output

Check the console for output.

Expected Behavior

Using queryRenderedFeatures on an even number of overlapping Polygons in a MultiPolygon should work detect the MultiPolygon.

Actual Behavior

Using queryRenderedFeatures on an even number of overlapping Polygons in a MultiPolygon does not detect the MultiPolygon.

[LostDragonist]

I have traced this issue back to this: https://github.com/LostDragonist/maplibre-gl-js/blob/main/src/util/intersection_tests.ts#L144

c is being flipped between true and false as part of the polygon ray-tracing algorithm. That's fine. The issues are that:

1. c is not being reset between polygons. This has the potential to lead to some false-positives (theoretically? haven't reproduced that yet)
2. When c == true after processing a complete polygon, the entire function should return true as being within any Polygon of a MultiPolygon means you are within that MultiPolygon. There's not the same concept of "holes" that Polygons have. The MultiPolygon rendering supports this fact.

I'll be working up a PR for this shortly.

[HarelM]

Is this considered a valid multipolygon, where two polygons overlap each other?

[LostDragonist]

Nothing in RFC 7946 (current or previous revisions) calls it out as being invalid or having special considerations.

There's actually already a query integration test in place that uses a multipolygon with two overlapping polygons. The reason that one currently works is that it tests against a bounding box instead of just point. Therefore it hits a different code path that doesn't have the same issues.