[core, ios, osx, android, glfw] Flipped origin of Map::latLngForPixel(), Map::pixelForLatLng()

Map and Transform methods assume an origin at the top-left corner of the view, like iOS, Android, and GLFW but unlike OS X. Transform is responsible for flipping coordinates between the top-left origin of Map and the bottom-left origin of TransformState.

Fixes #3574.

3 files changed, 26 insertions, 4 deletions

diff --git a/src/mbgl/map/map.cpp b/src/mbgl/map/map.cpp
index b0cc49968c..e710ca4c14 100644
--- a/src/mbgl/map/map.cpp
+++ b/src/mbgl/map/map.cpp
@@ -259,12 +259,13 @@ CameraOptions Map::cameraForLatLngs(const std::vector<LatLng>& latLngs, const Ed
     // Calculate the bounds of the possibly rotated shape with respect to the viewport.
     PrecisionPoint nePixel = {-INFINITY, -INFINITY};
     PrecisionPoint swPixel = {INFINITY, INFINITY};
+    double viewportHeight = getHeight();
     for (LatLng latLng : latLngs) {
         PrecisionPoint pixel = pixelForLatLng(latLng);
         swPixel.x = std::min(swPixel.x, pixel.x);
         nePixel.x = std::max(nePixel.x, pixel.x);
-        swPixel.y = std::min(swPixel.y, pixel.y);
-        nePixel.y = std::max(nePixel.y, pixel.y);
+        swPixel.y = std::min(swPixel.y, viewportHeight - pixel.y);
+        nePixel.y = std::max(nePixel.y, viewportHeight - pixel.y);
     }
     double width = nePixel.x - swPixel.x;
     double height = nePixel.y - swPixel.y;
@@ -289,6 +290,9 @@ CameraOptions Map::cameraForLatLngs(const std::vector<LatLng>& latLngs, const Ed
         (paddedNEPixel.x + paddedSWPixel.x) / 2,
         (paddedNEPixel.y + paddedSWPixel.y) / 2,
     };
+    
+    // CameraOptions origin is at the top-left corner.
+    centerPixel.y = viewportHeight - centerPixel.y;
 
     options.center = latLngForPixel(centerPixel);
     options.zoom = zoom;
@@ -397,11 +401,11 @@ LatLng Map::latLngForProjectedMeters(const ProjectedMeters& projectedMeters) con
 }
 
 PrecisionPoint Map::pixelForLatLng(const LatLng& latLng) const {
-    return transform->getState().latLngToPoint(latLng);
+    return transform->latLngToPoint(latLng);
 }
 
 LatLng Map::latLngForPixel(const PrecisionPoint& pixel) const {
-    return transform->getState().pointToLatLng(pixel);
+    return transform->pointToLatLng(pixel);
 }
 
 #pragma mark - Annotations
diff --git a/src/mbgl/map/transform.cpp b/src/mbgl/map/transform.cpp
index 69af657ecd..1363e2abd5 100644
--- a/src/mbgl/map/transform.cpp
+++ b/src/mbgl/map/transform.cpp
@@ -641,3 +641,17 @@ void Transform::cancelTransitions() {
 void Transform::setGestureInProgress(bool inProgress) {
     state.gestureInProgress = inProgress;
 }
+
+#pragma mark Conversion and projection
+
+PrecisionPoint Transform::latLngToPoint(const LatLng& latLng) const {
+    PrecisionPoint point = state.latLngToPoint(latLng);
+    point.y = state.height - point.y;
+    return point;
+}
+
+LatLng Transform::pointToLatLng(const PrecisionPoint& point) const {
+    PrecisionPoint flippedPoint = point;
+    flippedPoint.y = state.height - flippedPoint.y;
+    return state.pointToLatLng(flippedPoint);
+}
diff --git a/src/mbgl/map/transform.hpp b/src/mbgl/map/transform.hpp
index cb3378a532..bef6c6c87e 100644
--- a/src/mbgl/map/transform.hpp
+++ b/src/mbgl/map/transform.hpp
@@ -123,6 +123,10 @@ public:
     bool isRotating() const { return state.isRotating(); }
     bool isScaling() const { return state.isScaling(); }
     bool isPanning() const { return state.isPanning(); }
+    
+    // Conversion and projection
+    PrecisionPoint latLngToPoint(const LatLng&) const;
+    LatLng pointToLatLng(const PrecisionPoint&) const;
 
 private:
     void unwrapLatLng(LatLng&);