[ios] Round tap-zoom gestures to nearest integer

Round double-tap and two-finger tap zoom gestures to the nearest integer zoom level. This has the benefits for raster tiles, as well as styles with zoom-based functions.

This results in a wider possible zoom range — ~0.5-1.5:

Old: z4.6 → z5.6 (+1.0), z4.4 → z5.4 (+1.0)
New: z4.6 → z6.0 (+1.4), z4.4 → z5.0 (+0.6)

2 files changed, 12 insertions, 8 deletions

diff --git a/platform/ios/CHANGELOG.md b/platform/ios/CHANGELOG.md
index c81ae31e2c..5a299b9186 100644
--- a/platform/ios/CHANGELOG.md
+++ b/platform/ios/CHANGELOG.md
@@ -42,6 +42,7 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 * Added a `MGLDistanceFormatter` class for formatting geographic distances. ([#7888](https://github.com/mapbox/mapbox-gl-native/pull/7888))
 * Added a method to MGLMapViewDelegate, `-mapView:shouldChangeFromCamera:toCamera:`, that you can implement to restrict which parts the user can navigate to using gestures. ([#5584](https://github.com/mapbox/mapbox-gl-native/pull/5584))
 * Annotations are no longer deselected when the map is panned or zoomed, even if the annotation moves out of the visible bounds. ([#8022](https://github.com/mapbox/mapbox-gl-native/pull/8022))
+* Double-tap and two-finger tap gestures now zoom to the nearest integer zoom level. ([#8027](https://github.com/mapbox/mapbox-gl-native/pull/8027))
 
 ## 3.4.1 - January 25, 2017
 
diff --git a/platform/ios/src/MGLMapView.mm b/platform/ios/src/MGLMapView.mm
index 77fd810e16..0b0bf4a34b 100644
--- a/platform/ios/src/MGLMapView.mm
+++ b/platform/ios/src/MGLMapView.mm
@@ -1556,10 +1556,12 @@ public:
     if (doubleTap.state == UIGestureRecognizerStateEnded)
     {
         MGLMapCamera *oldCamera = self.camera;
-        
+
+        double newZoom = round(self.zoomLevel) + 1.0;
+
         CGPoint gesturePoint = [self anchorPointForGesture:doubleTap];
-        
-        MGLMapCamera *toCamera = [self cameraByZoomingToZoomLevel:self.zoomLevel + 1.0 aroundAnchorPoint:gesturePoint];
+
+        MGLMapCamera *toCamera = [self cameraByZoomingToZoomLevel:newZoom aroundAnchorPoint:gesturePoint];
         
         if (![self.delegate respondsToSelector:@selector(mapView:shouldChangeFromCamera:toCamera:)] ||
             [self.delegate mapView:self shouldChangeFromCamera:oldCamera toCamera:toCamera])
@@ -1567,7 +1569,7 @@ public:
             [self trackGestureEvent:MGLEventGestureDoubleTap forRecognizer:doubleTap];
             
             mbgl::ScreenCoordinate center(gesturePoint.x, gesturePoint.y);
-            _mbglMap->scaleBy(2, center, MGLDurationInSecondsFromTimeInterval(MGLAnimationDuration));
+            _mbglMap->setZoom(newZoom, center, MGLDurationInSecondsFromTimeInterval(MGLAnimationDuration));
             
             __weak MGLMapView *weakSelf = self;
             
@@ -1595,16 +1597,17 @@ public:
     {
         MGLMapCamera *oldCamera = self.camera;
 
-        double zoom = self.zoomLevel;
+        double newZoom = round(self.zoomLevel) - 1.0;
+
         CGPoint gesturePoint = [self anchorPointForGesture:twoFingerTap];
-        
-        MGLMapCamera *toCamera = [self cameraByZoomingToZoomLevel:zoom - 1.0 aroundAnchorPoint:gesturePoint];
+
+        MGLMapCamera *toCamera = [self cameraByZoomingToZoomLevel:newZoom aroundAnchorPoint:gesturePoint];
         
         if (![self.delegate respondsToSelector:@selector(mapView:shouldChangeFromCamera:toCamera:)] ||
             [self.delegate mapView:self shouldChangeFromCamera:oldCamera toCamera:toCamera])
         {
             mbgl::ScreenCoordinate center(gesturePoint.x, gesturePoint.y);
-            _mbglMap->scaleBy(0.5, center, MGLDurationInSecondsFromTimeInterval(MGLAnimationDuration));
+            _mbglMap->setZoom(newZoom, center, MGLDurationInSecondsFromTimeInterval(MGLAnimationDuration));
             
             __weak MGLMapView *weakSelf = self;