[ios] Optimize MGLAnnotationView scale transform when not pitchedupstream/fb-unpitched-annotation-view-scaling

3 files changed, 18 insertions, 3 deletions

diff --git a/platform/ios/CHANGELOG.md b/platform/ios/CHANGELOG.md
index e1e142fc14..0172ad7afb 100644
--- a/platform/ios/CHANGELOG.md
+++ b/platform/ios/CHANGELOG.md
@@ -17,6 +17,10 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 
 * Fixed a memory leak that occurred when creating a map snapshot. ([#10585](https://github.com/mapbox/mapbox-gl-native/pull/10585))
 
+### Annotations
+
+* Improved performance of `MGLAnnotationView`-backed annotations that have `scalesWithViewingDistance` enabled. ([#10951](https://github.com/mapbox/mapbox-gl-native/pull/10951))
+
 ### Other changes
 
 * Long-pressing the attribution button causes the SDK’s version number to be displayed in the action sheet that appears. ([#10650](https://github.com/mapbox/mapbox-gl-native/pull/10650))
diff --git a/platform/ios/src/MGLAnnotationView.h b/platform/ios/src/MGLAnnotationView.h
index 4fa0f196ab..8006ec3e40 100644
--- a/platform/ios/src/MGLAnnotationView.h
+++ b/platform/ios/src/MGLAnnotationView.h
@@ -171,6 +171,10 @@ MGL_EXPORT
 
  The default value of this property is `YES`. Set this property to `NO` if the
  view’s legibility is important.
+
+ @note Scaling many on-screen annotation views can contribute to poor map
+    performance. Consider disabling this property if your use case involves
+    hundreds or thousands of annotation views.
  */
 @property (nonatomic, assign) BOOL scalesWithViewingDistance;
 
diff --git a/platform/ios/src/MGLAnnotationView.mm b/platform/ios/src/MGLAnnotationView.mm
index 94d0649413..4585479582 100644
--- a/platform/ios/src/MGLAnnotationView.mm
+++ b/platform/ios/src/MGLAnnotationView.mm
@@ -12,6 +12,7 @@
 @property (nonatomic, readwrite, nullable) NSString *reuseIdentifier;
 @property (nonatomic, readwrite) CATransform3D lastAppliedScaleTransform;
 @property (nonatomic, readwrite) CATransform3D lastAppliedRotateTransform;
+@property (nonatomic, readwrite) CGFloat lastPitch;
 @property (nonatomic, weak) UIPanGestureRecognizer *panGestureRecognizer;
 @property (nonatomic, weak) UILongPressGestureRecognizer *longPressRecognizer;
 @property (nonatomic, weak) MGLMapView *mapView;
@@ -137,12 +138,18 @@
         // along the y axis of its superview.
         CGFloat maxScaleReduction = 1.0 - self.center.y / superviewHeight;
 
+        // Since it is possible for the map view to report a pitch less than 0 due to the nature of
+        // how the gesture information is captured, the value is guarded with MAX.
+        CGFloat pitch = MAX(self.mapView.camera.pitch, 0);
+
+        // Return early if the map view currently has no pitch and was not previously pitched.
+        if (!pitch && !_lastPitch) return;
+        _lastPitch = pitch;
+
         // The pitch intensity represents how much the map view is actually pitched compared to
         // what is possible. The value will range from 0% (not pitched at all) to 100% (pitched as much
         // as the map view will allow). The map view's maximum pitch is defined in `mbgl::util::PITCH_MAX`.
-        // Since it is possible for the map view to report a pitch less than 0 due to the nature of
-        // how the gesture information is captured, the value is guarded with MAX.
-        CGFloat pitchIntensity = MAX(self.mapView.camera.pitch, 0) / MGLDegreesFromRadians(mbgl::util::PITCH_MAX);
+        CGFloat pitchIntensity = pitch / MGLDegreesFromRadians(mbgl::util::PITCH_MAX);
 
         // The pitch adjusted scale is the inverse proportion of the maximum possible scale reduction
         // multiplied by the pitch intensity. For example, if the maximum scale reduction is 75% and the