Fix #1975 - improve animation fluidity and response

platform/ios/MGLMapView.mm

@@ -53,6 +53,7 @@
 const CGFloat MGLMaximumPitch = 60;
 const CLLocationDegrees MGLAngularFieldOfView = M_PI / 6.;
 const std::string spritePrefix = "com.mapbox.sprites.";
+const NSUInteger MGLTargetFrameInterval = 2;  //Target FPS will be 60 divided by this value
 
 NSString *const MGLAnnotationIDKey = @"MGLAnnotationIDKey";
 NSString *const MGLAnnotationSymbolKey = @"MGLAnnotationSymbolKey";
@@ -124,6 +125,9 @@ @implementation MGLMapView
 
     CLLocationDegrees _pendingLatitude;
     CLLocationDegrees _pendingLongitude;
+
+    CADisplayLink *_displayLink;
+    BOOL _needsDisplayRefresh;
 }
 
 #pragma mark - Setup & Teardown -
@@ -226,6 +230,12 @@ - (void)commonInit
     // setup mbgl map
     _mbglMap = new mbgl::Map(*_mbglView, *_mbglFileSource, mbgl::MapMode::Continuous);
 
+    // setup refresh driver
+    _displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(updateFromDisplayLink)];
+    _displayLink.frameInterval = MGLTargetFrameInterval;
+    [_displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
+    _needsDisplayRefresh = YES;
+
     // start paused if in IB
     if (_isTargetingInterfaceBuilder || background) {
         self.dormant = YES;
@@ -386,7 +396,7 @@ - (void)createGLView
     //
     _glView = [[GLKView alloc] initWithFrame:self.bounds context:_context];
     _glView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
-    _glView.enableSetNeedsDisplay = YES;
+    _glView.enableSetNeedsDisplay = NO;
     _glView.drawableStencilFormat = GLKViewDrawableStencilFormat8;
     _glView.drawableDepthFormat = GLKViewDrawableDepthFormat16;
     _glView.contentScaleFactor = [UIScreen instancesRespondToSelector:@selector(nativeScale)] ? [[UIScreen mainScreen] nativeScale] : [[UIScreen mainScreen] scale];
@@ -734,6 +744,25 @@ - (void)layoutSubviews
 
 #pragma mark - Life Cycle -
 
+- (void)updateFromDisplayLink
+{
+    MGLAssertIsMainThread();
+
+    if (_needsDisplayRefresh)
+    {
+        _needsDisplayRefresh = NO;
+
+        [self.glView display];
+    }
+}
+
+- (void)invalidate
+{
+    MGLAssertIsMainThread();
+
+    _needsDisplayRefresh = YES;
+}
+
 - (void)willTerminate
 {
     MGLAssertIsMainThread();
@@ -3104,12 +3133,6 @@ + (NSString *)pathForBundleResourceNamed:(NSString *)name ofType:(NSString *)ext
     return path;
 }
 
-- (void)invalidate
-{
-    MGLAssertIsMainThread();
-    [self.glView setNeedsDisplay];
-}
-
 - (BOOL)isFullyLoaded
 {
     return _mbglMap->isFullyLoaded();