[core] Camera center and anchor points are mutually exclusive

3 files changed, 20 insertions, 2 deletions

diff --git a/include/mbgl/map/camera.hpp b/include/mbgl/map/camera.hpp
index 33722a0018..d5563b5ccf 100644
--- a/include/mbgl/map/camera.hpp
+++ b/include/mbgl/map/camera.hpp
@@ -10,7 +10,10 @@
 namespace mbgl {
 
 /** Various options for describing the viewpoint of a map. All fields are
-    optional. */
+    optional.
+    Anchor and center points are mutually exclusive, with preference for the
+    center point when both are set.
+    */
 struct CameraOptions {
     /** Coordinate at the center of the map. */
     optional<LatLng> center;
diff --git a/src/mbgl/map/transform.cpp b/src/mbgl/map/transform.cpp
index 0d633499cf..03a1e117f7 100644
--- a/src/mbgl/map/transform.cpp
+++ b/src/mbgl/map/transform.cpp
@@ -561,7 +561,9 @@ void Transform::startTransition(const CameraOptions& camera,
     observer.onCameraWillChange(isAnimated ? MapObserver::CameraChangeMode::Animated : MapObserver::CameraChangeMode::Immediate);
 
     // Associate the anchor, if given, with a coordinate.
-    optional<ScreenCoordinate> anchor = camera.anchor;
+    // Anchor and center points are mutually exclusive, with preference for the
+    // center point when both are set.
+    optional<ScreenCoordinate> anchor = camera.center ? nullopt : camera.anchor;
     LatLng anchorLatLng;
     if (anchor) {
         anchor->y = state.size.height - anchor->y;
diff --git a/test/map/transform.test.cpp b/test/map/transform.test.cpp
index 44b5f49366..06df34c4c4 100644
--- a/test/map/transform.test.cpp
+++ b/test/map/transform.test.cpp
@@ -476,6 +476,19 @@ TEST(Transform, Camera) {
     transform.updateTransitions(transform.getTransitionStart() + Milliseconds(750));
     transform.updateTransitions(transform.getTransitionStart() + transform.getTransitionDuration());
     ASSERT_FALSE(transform.inTransition());
+
+    // Anchor and center points are mutually exclusive.
+    CameraOptions camera;
+    camera.center = LatLng { 0, 0 };
+    camera.anchor = ScreenCoordinate { 0, 0 }; // top-left
+    camera.zoom = transform.getState().getMaxZoom();
+    transform.easeTo(camera, AnimationOptions(Seconds(1)));
+    transform.updateTransitions(transform.getTransitionStart() + Milliseconds(250));
+    transform.updateTransitions(transform.getTransitionStart() + Milliseconds(500));
+    transform.updateTransitions(transform.getTransitionStart() + Milliseconds(750));
+    transform.updateTransitions(transform.getTransitionStart() + transform.getTransitionDuration());
+    ASSERT_DOUBLE_EQ(transform.getLatLng().latitude(), 0);
+    ASSERT_DOUBLE_EQ(transform.getLatLng().longitude(), 0);
 }
 
 TEST(Transform, DefaultTransform) {