[ios] Add annotation container view (#5194)

Add a container view to hold annotations. This gets around a performance
issue with `UIView:addSubview:` where adding views is N^2. It helps
annotation views avoid cutting into callout views when the annotation
views are transformed to be "flat".

7 files changed, 114 insertions, 7 deletions

diff --git a/platform/ios/app/MBXAnnotationView.m b/platform/ios/app/MBXAnnotationView.m
index 8cbe07a367..890881a316 100644
--- a/platform/ios/app/MBXAnnotationView.m
+++ b/platform/ios/app/MBXAnnotationView.m
@@ -12,7 +12,7 @@
     [super layoutSubviews];
     if (!self.centerView) {
         self.backgroundColor = [UIColor blueColor];
-        self.centerView = [[UIView alloc] initWithFrame:CGRectInset(self.bounds, 5.0, 5.0)];
+        self.centerView = [[UIView alloc] initWithFrame:CGRectInset(self.bounds, 1.0, 1.0)];
         self.centerView.backgroundColor = self.centerColor;
         [self addSubview:self.centerView];
     }
diff --git a/platform/ios/app/MBXViewController.m b/platform/ios/app/MBXViewController.m
index c72bdfd0f8..70f777422d 100644
--- a/platform/ios/app/MBXViewController.m
+++ b/platform/ios/app/MBXViewController.m
@@ -574,14 +574,28 @@ static NSString * const MBXViewControllerAnnotationViewReuseIdentifer = @"MBXVie
 
 - (MGLAnnotationView *)mapView:(MGLMapView *)mapView viewForAnnotation:(id<MGLAnnotation>)annotation
 {
+    // Use GL backed pins for dropped pin annotations
+    if ([annotation isMemberOfClass:[MBXDroppedPinAnnotation class]])
+    {
+        return nil;
+    }
+    
     MBXAnnotationView *annotationView = (MBXAnnotationView *)[mapView dequeueReusableAnnotationViewWithIdentifier:MBXViewControllerAnnotationViewReuseIdentifer];
     if (!annotationView)
     {
         annotationView = [[MBXAnnotationView alloc] initWithReuseIdentifier:MBXViewControllerAnnotationViewReuseIdentifer];
-        annotationView.frame = CGRectMake(0, 0, 40, 40);
+        annotationView.frame = CGRectMake(0, 0, 10, 10);
         annotationView.centerColor = [UIColor whiteColor];
-        annotationView.flat = YES;
-        annotationView.scalesWithViewingDistance = YES;
+       
+        // uncomment to flatten the annotation view against the map when the map is tilted
+        // this currently causes severe performance issues when more than 2k annotations are visible
+        // annotationView.flat = YES;
+       
+        // uncomment to force annotation view to maintain a constant size when the map is tilted
+        // by default, annotation views will shrink and grow as the move towards and away from the
+        // horizon. Relatedly, annotations backed by GL sprites ONLY scale with viewing distance currently.
+        // annotationView.scalesWithViewingDistance = NO;
+        
     } else {
         // orange indicates that the annotation view was reused
         annotationView.centerColor = [UIColor orangeColor];
diff --git a/platform/ios/ios.xcodeproj/project.pbxproj b/platform/ios/ios.xcodeproj/project.pbxproj
index 811fb89b7d..9c8343f890 100644
--- a/platform/ios/ios.xcodeproj/project.pbxproj
+++ b/platform/ios/ios.xcodeproj/project.pbxproj
@@ -12,6 +12,9 @@
 		4018B1C91CDC288A00F666AF /* MGLAnnotationView_Private.h in Headers */ = {isa = PBXBuildFile; fileRef = 4018B1C31CDC277F00F666AF /* MGLAnnotationView_Private.h */; };
 		4018B1CA1CDC288E00F666AF /* MGLAnnotationView.h in Headers */ = {isa = PBXBuildFile; fileRef = 4018B1C51CDC277F00F666AF /* MGLAnnotationView.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		4018B1CB1CDC288E00F666AF /* MGLAnnotationView.h in Headers */ = {isa = PBXBuildFile; fileRef = 4018B1C51CDC277F00F666AF /* MGLAnnotationView.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		40EDA1C01CFE0E0200D9EA68 /* MGLAnnotationContainerView.h in Headers */ = {isa = PBXBuildFile; fileRef = 40EDA1BD1CFE0D4A00D9EA68 /* MGLAnnotationContainerView.h */; };
+		40EDA1C11CFE0E0500D9EA68 /* MGLAnnotationContainerView.m in Sources */ = {isa = PBXBuildFile; fileRef = 40EDA1BE1CFE0D4A00D9EA68 /* MGLAnnotationContainerView.m */; };
+		40EDA1C21CFE0E0500D9EA68 /* MGLAnnotationContainerView.m in Sources */ = {isa = PBXBuildFile; fileRef = 40EDA1BE1CFE0D4A00D9EA68 /* MGLAnnotationContainerView.m */; };
 		40FDA76B1CCAAA6800442548 /* MBXAnnotationView.m in Sources */ = {isa = PBXBuildFile; fileRef = 40FDA76A1CCAAA6800442548 /* MBXAnnotationView.m */; };
 		DA0CD5901CF56F6A00A5F5A5 /* MGLFeatureTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = DA0CD58F1CF56F6A00A5F5A5 /* MGLFeatureTests.mm */; };
 		DA17BE301CC4BAC300402C41 /* MGLMapView_Internal.h in Headers */ = {isa = PBXBuildFile; fileRef = DA17BE2F1CC4BAC300402C41 /* MGLMapView_Internal.h */; };
@@ -324,6 +327,8 @@
 		4018B1C41CDC277F00F666AF /* MGLAnnotationView.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = MGLAnnotationView.mm; sourceTree = "<group>"; };
 		4018B1C51CDC277F00F666AF /* MGLAnnotationView.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLAnnotationView.h; sourceTree = "<group>"; };
 		402E9DE01CD2C76200FD4519 /* Mapbox.playground */ = {isa = PBXFileReference; lastKnownFileType = file.playground; path = Mapbox.playground; sourceTree = "<group>"; };
+		40EDA1BD1CFE0D4A00D9EA68 /* MGLAnnotationContainerView.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLAnnotationContainerView.h; sourceTree = "<group>"; };
+		40EDA1BE1CFE0D4A00D9EA68 /* MGLAnnotationContainerView.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MGLAnnotationContainerView.m; sourceTree = "<group>"; };
 		40FDA7691CCAAA6800442548 /* MBXAnnotationView.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MBXAnnotationView.h; sourceTree = "<group>"; };
 		40FDA76A1CCAAA6800442548 /* MBXAnnotationView.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MBXAnnotationView.m; sourceTree = "<group>"; };
 		DA0CD58F1CF56F6A00A5F5A5 /* MGLFeatureTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; name = MGLFeatureTests.mm; path = ../../darwin/test/MGLFeatureTests.mm; sourceTree = "<group>"; };
@@ -897,9 +902,11 @@
 		DAD165841CF4D06B001FF4B9 /* Annotations */ = {
 			isa = PBXGroup;
 			children = (
+				40EDA1BD1CFE0D4A00D9EA68 /* MGLAnnotationContainerView.h */,
+				40EDA1BE1CFE0D4A00D9EA68 /* MGLAnnotationContainerView.m */,
 				4018B1C31CDC277F00F666AF /* MGLAnnotationView_Private.h */,
-				4018B1C41CDC277F00F666AF /* MGLAnnotationView.mm */,
 				4018B1C51CDC277F00F666AF /* MGLAnnotationView.h */,
+				4018B1C41CDC277F00F666AF /* MGLAnnotationView.mm */,
 				DA8848341CBAFB8500AB86E3 /* MGLAnnotationImage.h */,
 				DA8848401CBAFB9800AB86E3 /* MGLAnnotationImage_Private.h */,
 				DA8848411CBAFB9800AB86E3 /* MGLAnnotationImage.m */,
@@ -977,6 +984,7 @@
 				DA8847F81CBAFA5100AB86E3 /* MGLPointAnnotation.h in Headers */,
 				DA8847F31CBAFA5100AB86E3 /* MGLMultiPoint.h in Headers */,
 				DAD1656C1CF41981001FF4B9 /* MGLFeature.h in Headers */,
+				40EDA1C01CFE0E0200D9EA68 /* MGLAnnotationContainerView.h in Headers */,
 				DA88484F1CBAFB9800AB86E3 /* MGLAnnotationImage_Private.h in Headers */,
 				DA8847F21CBAFA5100AB86E3 /* MGLMapCamera.h in Headers */,
 				DA8847F51CBAFA5100AB86E3 /* MGLOfflineRegion.h in Headers */,
@@ -1347,6 +1355,7 @@
 			files = (
 				DA88485D1CBAFB9800AB86E3 /* MGLUserLocationAnnotationView.m in Sources */,
 				DAD165701CF41981001FF4B9 /* MGLFeature.mm in Sources */,
+				40EDA1C11CFE0E0500D9EA68 /* MGLAnnotationContainerView.m in Sources */,
 				DA8848541CBAFB9800AB86E3 /* MGLCompactCalloutView.m in Sources */,
 				DA8848251CBAFA6200AB86E3 /* MGLPointAnnotation.m in Sources */,
 				DA88482D1CBAFA6200AB86E3 /* NSBundle+MGLAdditions.m in Sources */,
@@ -1387,6 +1396,7 @@
 			files = (
 				DAA4E4221CBB730400178DFB /* MGLPointAnnotation.m in Sources */,
 				DAD165711CF41981001FF4B9 /* MGLFeature.mm in Sources */,
+				40EDA1C21CFE0E0500D9EA68 /* MGLAnnotationContainerView.m in Sources */,
 				DAA4E4291CBB730400178DFB /* NSBundle+MGLAdditions.m in Sources */,
 				DAA4E42E1CBB730400178DFB /* MGLAPIClient.m in Sources */,
 				DAA4E4201CBB730400178DFB /* MGLOfflinePack.mm in Sources */,
diff --git a/platform/ios/src/MGLAnnotationContainerView.h b/platform/ios/src/MGLAnnotationContainerView.h
new file mode 100644
index 0000000000..90d2964831
--- /dev/null
+++ b/platform/ios/src/MGLAnnotationContainerView.h
@@ -0,0 +1,17 @@
+#import <UIKit/UIKit.h>
+
+#import "MGLTypes.h"
+
+@class MGLAnnotationView;
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface MGLAnnotationContainerView : UIView
+
++ (instancetype)annotationContainerViewWithAnnotationContainerView:(MGLAnnotationContainerView *)annotationContainerView;
+
+- (void)addSubviews:(NS_ARRAY_OF(MGLAnnotationView *) *)subviews;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/platform/ios/src/MGLAnnotationContainerView.m b/platform/ios/src/MGLAnnotationContainerView.m
new file mode 100644
index 0000000000..cd9c990ef0
--- /dev/null
+++ b/platform/ios/src/MGLAnnotationContainerView.m
@@ -0,0 +1,38 @@
+#import "MGLAnnotationContainerView.h"
+#import "MGLAnnotationView.h"
+
+@interface MGLAnnotationContainerView ()
+
+@property (nonatomic) NS_MUTABLE_ARRAY_OF(MGLAnnotationView *) *annotationViews;
+
+@end
+
+@implementation MGLAnnotationContainerView
+
+- (instancetype)initWithFrame:(CGRect)frame
+{
+    self = [super initWithFrame:frame];
+    if (self)
+    {
+        _annotationViews = [NSMutableArray array];
+    }
+    return self;
+}
+
++ (instancetype)annotationContainerViewWithAnnotationContainerView:(nonnull MGLAnnotationContainerView *)annotationContainerView
+{
+    MGLAnnotationContainerView *newAnnotationContainerView = [[MGLAnnotationContainerView alloc] initWithFrame:annotationContainerView.frame];
+    [newAnnotationContainerView addSubviews:annotationContainerView.subviews];
+    return newAnnotationContainerView;
+}
+
+- (void)addSubviews:(NS_ARRAY_OF(MGLAnnotationView *) *)subviews
+{
+    for (MGLAnnotationView *view in subviews)
+    {
+        [self addSubview:view];
+        [self.annotationViews addObject:view];
+    }
+}
+
+@end
diff --git a/platform/ios/src/MGLAnnotationView.mm b/platform/ios/src/MGLAnnotationView.mm
index 1574da81b2..6f1d94c3e7 100644
--- a/platform/ios/src/MGLAnnotationView.mm
+++ b/platform/ios/src/MGLAnnotationView.mm
@@ -8,6 +8,7 @@
 
 @property (nonatomic) id<MGLAnnotation> annotation;
 @property (nonatomic, readwrite, nullable) NSString *reuseIdentifier;
+
 @end
 
 @implementation MGLAnnotationView
diff --git a/platform/ios/src/MGLMapView.mm b/platform/ios/src/MGLMapView.mm
index 59830b094f..e5a65d42ea 100644
--- a/platform/ios/src/MGLMapView.mm
+++ b/platform/ios/src/MGLMapView.mm
@@ -41,6 +41,7 @@
 #import "MGLAnnotationView_Private.h"
 #import "MGLMapboxEvents.h"
 #import "MGLCompactCalloutView.h"
+#import "MGLAnnotationContainerView.h"
 
 #import <algorithm>
 #import <cstdlib>
@@ -233,6 +234,7 @@ public:
 @property (nonatomic, getter=isDormant) BOOL dormant;
 @property (nonatomic, readonly, getter=isRotationAllowed) BOOL rotationAllowed;
 @property (nonatomic) MGLMapViewProxyAccessibilityElement *mapViewProxyAccessibilityElement;
+@property (nonatomic) MGLAnnotationContainerView *annotationContainerView;
 
 @end
 
@@ -548,7 +550,6 @@ mbgl::Duration MGLDurationInSeconds(NSTimeInterval duration)
     _glView.delegate = self;
     [_glView bindDrawable];
     [self insertSubview:_glView atIndex:0];
-
     _glView.contentMode = UIViewContentModeCenter;
 
     // load extensions
@@ -2805,6 +2806,8 @@ mbgl::Duration MGLDurationInSeconds(NSTimeInterval duration)
 
     BOOL delegateImplementsViewForAnnotation = [self.delegate respondsToSelector:@selector(mapView:viewForAnnotation:)];
     BOOL delegateImplementsImageForPoint = [self.delegate respondsToSelector:@selector(mapView:imageForAnnotation:)];
+    
+    NSMutableArray *newAnnotationViews = [[NSMutableArray alloc] initWithCapacity:annotations.count];
 
     for (id <MGLAnnotation> annotation in annotations)
     {
@@ -2839,7 +2842,7 @@ mbgl::Duration MGLDurationInSeconds(NSTimeInterval duration)
                 {
                     annotationViewsForAnnotation[annotationValue] = annotationView;
                     annotationView.center = [self convertCoordinate:annotation.coordinate toPointToView:self];
-                    [self.glView addSubview:annotationView];
+                    [newAnnotationViews addObject:annotationView];
                 }
             }
             
@@ -2927,10 +2930,34 @@ mbgl::Duration MGLDurationInSeconds(NSTimeInterval duration)
         }
     }
     
+    [self updateAnnotationContainerViewWithAnnotationViews:newAnnotationViews];
+    
     [self didChangeValueForKey:@"annotations"];
     UIAccessibilityPostNotification(UIAccessibilityLayoutChangedNotification, nil);
 }
 
+- (void)updateAnnotationContainerViewWithAnnotationViews:(NS_ARRAY_OF(MGLAnnotationView *) *)annotationViews
+{
+    if (annotationViews.count == 0) return;
+    
+    MGLAnnotationContainerView *newAnnotationContainerView;
+    if (self.annotationContainerView)
+    {
+        // reload any previously added views
+        newAnnotationContainerView = [MGLAnnotationContainerView annotationContainerViewWithAnnotationContainerView:self.annotationContainerView];
+        [self.annotationContainerView removeFromSuperview];
+    }
+    else
+    {
+        newAnnotationContainerView = [[MGLAnnotationContainerView alloc] initWithFrame:self.bounds];
+    }
+    newAnnotationContainerView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
+    newAnnotationContainerView.contentMode = UIViewContentModeCenter;
+    [newAnnotationContainerView addSubviews:annotationViews];
+    [_glView insertSubview:newAnnotationContainerView atIndex:0];
+    self.annotationContainerView = newAnnotationContainerView;
+}
+
 /// Initialize and return a default annotation image that depicts a round pin
 /// rising from the center, with a shadow slightly below center. The alignment
 /// rect therefore excludes the bottom half.