[core, ios, osx] Tilt around visual center point

The tilt gesture on both iOS and OS X now respects the content insets. On iOS, in user tracking mode, it additionally respects the user dot’s position if it’s aligned to the top or bottom of the view.

include/mbgl/map/map.hpp

@@ -130,6 +130,7 @@ public:
 
     // Pitch
     void setPitch(double pitch, const Duration& = Duration::zero());
+    void setPitch(double pitch, const PrecisionPoint&, const Duration& = Duration::zero());
     double getPitch() const;
 
     // North Orientation

platform/android/src/jni.cpp

@@ -680,11 +680,12 @@ jdouble JNICALL nativeGetPitch(JNIEnv *env, jobject obj, jlong nativeMapViewPtr)
     return nativeMapView->getMap().getPitch();
 }
 
-void JNICALL nativeSetPitch(JNIEnv *env, jobject obj, jlong nativeMapViewPtr, jdouble pitch, jlong duration) {
+void JNICALL nativeSetPitch(JNIEnv *env, jobject obj, jlong nativeMapViewPtr, jdouble pitch, jlong milliseconds) {
     mbgl::Log::Debug(mbgl::Event::JNI, "nativeGetPitch");
     assert(nativeMapViewPtr != 0);
     NativeMapView *nativeMapView = reinterpret_cast<NativeMapView *>(nativeMapViewPtr);
-    nativeMapView->getMap().setPitch(pitch, mbgl::Milliseconds(duration));
+    mbgl::Duration duration((mbgl::Milliseconds(milliseconds)));
+    nativeMapView->getMap().setPitch(pitch, duration);
 }
 
 void JNICALL nativeScaleBy(JNIEnv *env, jobject obj, jlong nativeMapViewPtr, jdouble ds, jdouble cx,

platform/ios/src/MGLMapView.mm

@@ -1428,8 +1428,13 @@ mbgl::Duration MGLDurationInSeconds(NSTimeInterval duration)
         CGFloat slowdown = 20.0;
 
         CGFloat pitchNew = currentPitch - (gestureDistance / slowdown);
-
-        _mbglMap->setPitch(pitchNew);
+        
+        CGPoint centerPoint = self.contentCenter;
+        if (self.userTrackingMode != MGLUserTrackingModeNone)
+        {
+            centerPoint = self.userLocationAnnotationViewCenter;
+        }
+        _mbglMap->setPitch(pitchNew, centerPoint);
 
         [self notifyMapChange:mbgl::MapChangeRegionIsChanging];
     }

platform/osx/src/MGLMapView.mm

@@ -1207,7 +1207,7 @@ public:
                 [self didChangeValueForKey:@"direction"];
             }
             if (self.pitchEnabled) {
-                _mbglMap->setPitch(_pitchAtBeginningOfGesture + delta.y / 5);
+                _mbglMap->setPitch(_pitchAtBeginningOfGesture + delta.y / 5, center);
             }
         }
     } else if (self.scrollEnabled) {

src/mbgl/map/map.cpp

@@ -357,7 +357,11 @@ void Map::resetNorth(const Duration& duration) {
 #pragma mark - Pitch
 
 void Map::setPitch(double pitch, const Duration& duration) {
-    transform->setPitch(pitch * M_PI / 180, duration);
+    setPitch(pitch, {NAN, NAN}, duration);
+}
+
+void Map::setPitch(double pitch, const PrecisionPoint& anchor, const Duration& duration) {
+    transform->setPitch(pitch * M_PI / 180, anchor, duration);
     update(Update::Repaint);
 }
 

src/mbgl/map/transform.cpp

@@ -523,12 +523,17 @@ double Transform::getAngle() const {
 #pragma mark - Pitch
 
 void Transform::setPitch(double pitch, const Duration& duration) {
+    setPitch(pitch, {NAN, NAN}, duration);
+}
+
+void Transform::setPitch(double pitch, const PrecisionPoint& anchor, const Duration& duration) {
     if (std::isnan(pitch)) {
         return;
     }
 
     CameraOptions camera;
     camera.pitch = pitch;
+    camera.anchor = anchor;
     easeTo(camera, duration);
 }
 

src/mbgl/map/transform.hpp

@@ -102,7 +102,15 @@ public:
     double getAngle() const;
 
     // Pitch
+    /** Sets the pitch angle.
+        @param angle The new pitch angle, measured in radians toward the
+            horizon. */
     void setPitch(double pitch, const Duration& = Duration::zero());
+    /** Sets the pitch angle, keeping the given point fixed within the view.
+        @param angle The new pitch angle, measured in radians toward the
+            horizon.
+        @param anchor A point relative to the top-left corner of the view. */
+    void setPitch(double pitch, const PrecisionPoint& anchor, const Duration& = Duration::zero());
     double getPitch() const;
 
     // North Orientation