[ios, osx] Avoid transition to current camera

Fixes #2456.

platform/darwin/MGLMapCamera.mm

@@ -98,4 +98,28 @@
             NSStringFromClass([self class]), self, _centerCoordinate.latitude, _centerCoordinate.longitude, _altitude, _heading, _pitch];
 }
 
+- (BOOL)isEqual:(id)other
+{
+    if ( ! [other isKindOfClass:[self class]])
+    {
+        return NO;
+    }
+    if (other == self)
+    {
+        return YES;
+    }
+    
+    MGLMapCamera *otherCamera = other;
+    return (_centerCoordinate.latitude == otherCamera.centerCoordinate.latitude
+            && _centerCoordinate.longitude == otherCamera.centerCoordinate.longitude
+            && _altitude == otherCamera.altitude
+            && _pitch == otherCamera.pitch && _heading == otherCamera.heading);
+}
+
+- (NSUInteger)hash
+{
+    return (@(_centerCoordinate.latitude).hash + @(_centerCoordinate.longitude).hash
+            + @(_altitude).hash + @(_pitch).hash + @(_heading).hash);
+}
+
 @end

platform/ios/src/MGLMapView.mm

@@ -1750,6 +1750,11 @@ std::chrono::steady_clock::duration MGLDurationInSeconds(float duration)
 
 - (void)setCamera:(MGLMapCamera *)camera withDuration:(NSTimeInterval)duration animationTimingFunction:(nullable CAMediaTimingFunction *)function completionHandler:(nullable void (^)(void))completion
 {
+    if ([self.camera isEqual:camera])
+    {
+        return;
+    }
+
     _mbglMap->cancelTransitions();
     mbgl::CameraOptions options = [self cameraOptionsObjectForAnimatingToCamera:camera];
     if (duration > 0)
@@ -1778,6 +1783,11 @@ std::chrono::steady_clock::duration MGLDurationInSeconds(float duration)
 
 - (void)flyToCamera:(MGLMapCamera *)camera withDuration:(NSTimeInterval)duration completionHandler:(nullable void (^)(void))completion
 {
+    if ([self.camera isEqual:camera])
+    {
+        return;
+    }
+
     _mbglMap->cancelTransitions();
     mbgl::CameraOptions options = [self cameraOptionsObjectForAnimatingToCamera:camera];
     if (duration >= 0)

platform/osx/src/MGLMapView.mm

@@ -946,6 +946,9 @@ public:
 
 - (void)setCamera:(MGLMapCamera *)camera withDuration:(NSTimeInterval)duration animationTimingFunction:(nullable CAMediaTimingFunction *)function completionHandler:(nullable void (^)(void))completion {
     _mbglMap->cancelTransitions();
+    if ([self.camera isEqual:camera]) {
+        return;
+    }
     
     mbgl::CameraOptions options = [self cameraOptionsObjectForAnimatingToCamera:camera];
     if (duration > 0) {
@@ -974,6 +977,9 @@ public:
 
 - (void)flyToCamera:(MGLMapCamera *)camera withDuration:(NSTimeInterval)duration completionHandler:(nullable void (^)(void))completion {
     _mbglMap->cancelTransitions();
+    if ([self.camera isEqual:camera]) {
+        return;
+    }
     
     mbgl::CameraOptions options = [self cameraOptionsObjectForAnimatingToCamera:camera];
     if (duration >= 0) {