[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.

4 files changed, 20 insertions, 37 deletions

diff --git a/src/mbgl/map/transform.cpp b/src/mbgl/map/transform.cpp
index 74e43a62fe..79b43f8901 100644
--- a/src/mbgl/map/transform.cpp
+++ b/src/mbgl/map/transform.cpp
@@ -95,12 +95,17 @@ void Transform::easeTo(const CameraOptions& camera, const AnimationOptions& anim
     if (camera.padding) {
         padding = *camera.padding;
     }
-    const LatLng startLatLng = getLatLng(padding);
+
+    LatLng startLatLng = getLatLng(padding);
+    startLatLng.unwrapForShortestPath(latLng);
+
+    // Make sure the end coordinate always remains valid.
+    latLng.wrap();
+
     const ScreenCoordinate startPoint = {
         state.lngX(startLatLng.longitude),
         state.latY(startLatLng.latitude),
     };
-    latLng.unwrapForShortestPath(getLatLng());
     const ScreenCoordinate endPoint = {
         state.lngX(latLng.longitude),
         state.latY(latLng.latitude),
@@ -136,7 +141,7 @@ void Transform::easeTo(const CameraOptions& camera, const AnimationOptions& anim
         ScreenCoordinate framePoint = util::interpolate(startPoint, endPoint, t);
         LatLng frameLatLng = {
             state.yLat(framePoint.y, startWorldSize),
-            state.xLng(framePoint.x, startWorldSize),
+            state.xLng(framePoint.x, startWorldSize)
         };
         double frameScale = util::interpolate(startScale, scale, t);
         state.setLatLngZoom(frameLatLng, state.scaleZoom(frameScale));
@@ -178,12 +183,17 @@ void Transform::flyTo(const CameraOptions &camera, const AnimationOptions &anima
     if (camera.padding) {
         padding = *camera.padding;
     }
-    const LatLng startLatLng = getLatLng(padding);
+
+    LatLng startLatLng = getLatLng(padding);
+    startLatLng.unwrapForShortestPath(latLng);
+
+    // Make sure the end coordinate always remains valid.
+    latLng.wrap();
+
     const ScreenCoordinate startPoint = {
         state.lngX(startLatLng.longitude),
         state.latY(startLatLng.latitude),
     };
-    latLng.unwrapForShortestPath(getLatLng());
     const ScreenCoordinate endPoint = {
         state.lngX(latLng.longitude),
         state.latY(latLng.latitude),
diff --git a/src/mbgl/map/transform_state.cpp b/src/mbgl/map/transform_state.cpp
index 006a8d5d3a..a23ee71f99 100644
--- a/src/mbgl/map/transform_state.cpp
+++ b/src/mbgl/map/transform_state.cpp
@@ -89,38 +89,11 @@ ConstrainMode TransformState::getConstrainMode() const {
 #pragma mark - Position
 
 LatLng TransformState::getLatLng(LatLng::WrapMode wrapMode) const {
-    LatLng ll {
+    return {
         util::RAD2DEG * (2 * std::atan(std::exp(y / Cc)) - 0.5 * M_PI),
         -x / Bc,
         wrapMode
     };
-
-    if (wrapMode == LatLng::Unwrapped) return ll;
-
-    // adjust for date line
-    double w = worldSize() / 2;
-    double x_ = x;
-    if (x_ > w) {
-        while (x_ > w) {
-            x_ -= w;
-            if (ll.longitude < 0) {
-                ll.longitude += util::LONGITUDE_MAX;
-            } else if (ll.longitude > 0) {
-                ll.longitude -= util::LONGITUDE_MAX;
-            }
-        }
-    } else if (x_ < -w) {
-        while (x_ < -w) {
-            x_ += w;
-            if (ll.longitude < 0) {
-                ll.longitude -= util::LONGITUDE_MAX;
-            } else if (ll.longitude > 0) {
-                ll.longitude -= util::LONGITUDE_MAX;
-            }
-        }
-    }
-
-    return ll;
 }
 
 double TransformState::pixel_x() const {
@@ -350,7 +323,7 @@ void TransformState::moveLatLng(const LatLng& latLng, const ScreenCoordinate& an
 
     auto centerCoord = latLngToTileCoord(getLatLng(LatLng::Unwrapped));
     auto latLngCoord = latLngToTileCoord(latLng);
-    auto anchorCoord = latLngToTileCoord(screenCoordinateToLatLng(anchor, LatLng::Unwrapped));
+    auto anchorCoord = latLngToTileCoord(screenCoordinateToLatLng(anchor));
     setLatLngZoom(tileCoordToLatLng(centerCoord + latLngCoord - anchorCoord), getZoom());
 }
 
diff --git a/src/mbgl/map/transform_state.hpp b/src/mbgl/map/transform_state.hpp
index 797a28692e..ef3a5dfefd 100644
--- a/src/mbgl/map/transform_state.hpp
+++ b/src/mbgl/map/transform_state.hpp
@@ -37,7 +37,7 @@ public:
     ConstrainMode getConstrainMode() const;
 
     // Position
-    LatLng getLatLng(LatLng::WrapMode = LatLng::Wrapped) const;
+    LatLng getLatLng(LatLng::WrapMode = LatLng::Unwrapped) const;
     double pixel_x() const;
     double pixel_y() const;
 
@@ -65,7 +65,7 @@ public:
 
     // Conversion and projection
     ScreenCoordinate latLngToScreenCoordinate(const LatLng&) const;
-    LatLng screenCoordinateToLatLng(const ScreenCoordinate&, LatLng::WrapMode = LatLng::Wrapped) const;
+    LatLng screenCoordinateToLatLng(const ScreenCoordinate&, LatLng::WrapMode = LatLng::Unwrapped) const;
 
     double xLng(double x, double worldSize) const;
     double yLat(double y, double worldSize) const;
diff --git a/src/mbgl/util/tile_cover.cpp b/src/mbgl/util/tile_cover.cpp
index 0fae940271..6efff4bb57 100644
--- a/src/mbgl/util/tile_cover.cpp
+++ b/src/mbgl/util/tile_cover.cpp
@@ -23,7 +23,7 @@ public:
     }
 
     static TileCoordinate fromScreenCoordinate(const TransformState& state, double zoom, const ScreenCoordinate& point) {
-        return fromLatLng(state, zoom, state.screenCoordinateToLatLng(point, LatLng::Unwrapped));
+        return fromLatLng(state, zoom, state.screenCoordinateToLatLng(point));
     }
 };