[core] Coordinate wrapping fixes

- Make returning LatLngs unwrapped by default.
- PointAnnotation and ShapeAnnotation are always wrapped so they can be
  selected via intersection from the visible tile boundaries.
- Fixes LatLng::wrap() calculation.
- Fixes LatLng::unwrapForShortestPath() calculation.

The new unwrapForShortestPath algorithm unwraps the start coordinate
either forwards or backwards depending on the end coordinate value, so
we can always cross the antimeridian when needed and still obtain a
wrapped end coordinate in the end.

Fixes #4214.

1 files changed, 11 insertions, 13 deletions

diff --git a/include/mbgl/util/geo.hpp b/include/mbgl/util/geo.hpp
index 56d575ceaa..9e2d7a2bb1 100644
--- a/include/mbgl/util/geo.hpp
+++ b/include/mbgl/util/geo.hpp
@@ -25,19 +25,17 @@ public:
     LatLng wrapped() const { return { latitude, longitude, Wrapped }; }
 
     void wrap() {
-        if (longitude < -util::LONGITUDE_MAX) longitude = std::fmod(longitude, util::LONGITUDE_MAX * 2);
-        if (longitude > util::LONGITUDE_MAX) longitude = -util::LONGITUDE_MAX + std::fmod(longitude, util::LONGITUDE_MAX);
-    }
-
-    /** If a path crossing the antemeridian would be shorter, extend the final
-      coordinate so that interpolating between the two endpoints will cross it. */
-    void unwrapForShortestPath(const LatLng& start) {
-        if (std::abs(start.longitude) + std::abs(longitude) > util::LONGITUDE_MAX) {
-            if (start.longitude > 0 && longitude < 0) {
-                longitude += util::DEGREES_MAX;
-            } else if (start.longitude < 0 && longitude > 0) {
-                longitude -= util::DEGREES_MAX;
-            }
+        if (longitude < -util::LONGITUDE_MAX) longitude = util::LONGITUDE_MAX + std::fmod(longitude + util::LONGITUDE_MAX, util::DEGREES_MAX);
+        if (longitude > util::LONGITUDE_MAX) longitude = -util::LONGITUDE_MAX + std::fmod(longitude + util::LONGITUDE_MAX, util::DEGREES_MAX);
+    }
+
+    // If we pass through the antimeridian, we update the start coordinate to make sure
+    // the end coordinate is always wrapped.
+    void unwrapForShortestPath(const LatLng& end) {
+        if (end.longitude < -util::LONGITUDE_MAX) {
+            longitude += util::DEGREES_MAX;
+        } else if (end.longitude > util::LONGITUDE_MAX) {
+            longitude -= util::DEGREES_MAX;
         }
     }