[macos] Map annotations to annotation tags

Optimized lookup of annotation tags by annotation from O(n) to a simple map lookup, for better performance and consistency with the iOS implementation of MGLMapView.

platform/macos/src/MGLMapView.mm

@@ -35,6 +35,7 @@
 #import <mbgl/util/chrono.hpp>
 #import <mbgl/util/run_loop.hpp>
 
+#import <map>
 #import <unordered_map>
 #import <unordered_set>
 
@@ -110,6 +111,9 @@ enum { MGLAnnotationTagNotFound = UINT32_MAX };
 /// the annotation itself.
 typedef std::unordered_map<MGLAnnotationTag, MGLAnnotationContext> MGLAnnotationTagContextMap;
 
+/// Mapping from an annotation object to an annotation tag.
+typedef std::map<id<MGLAnnotation>, MGLAnnotationTag> MGLAnnotationObjectTagMap;
+
 /// Returns an NSImage for the default marker image.
 NSImage *MGLDefaultMarkerImage() {
     NSString *path = [[NSBundle mgl_frameworkBundle] pathForResource:MGLDefaultStyleMarkerSymbolName
@@ -172,6 +176,7 @@ public:
     BOOL _didHideCursorDuringGesture;
 
     MGLAnnotationTagContextMap _annotationContextsByAnnotationTag;
+    MGLAnnotationObjectTagMap _annotationTagsByAnnotation;
     MGLAnnotationTag _selectedAnnotationTag;
     MGLAnnotationTag _lastSelectedAnnotationTag;
     /// Size of the rectangle formed by unioning the maximum slop area around every annotation image.
@@ -293,6 +298,7 @@ public:
     // Set up annotation management and selection state.
     _annotationImagesByIdentifier = [NSMutableDictionary dictionary];
     _annotationContextsByAnnotationTag = {};
+    _annotationTagsByAnnotation = {};
     _selectedAnnotationTag = MGLAnnotationTagNotFound;
     _lastSelectedAnnotationTag = MGLAnnotationTagNotFound;
     _annotationsNearbyLastClick = {};
@@ -1708,6 +1714,7 @@ public:
             MGLAnnotationContext context;
             context.annotation = annotation;
             _annotationContextsByAnnotationTag[annotationTag] = context;
+            _annotationTagsByAnnotation[annotation] = annotationTag;
 
             [(NSObject *)annotation addObserver:self forKeyPath:@"coordinates" options:0 context:(void *)(NSUInteger)annotationTag];
         } else if (![annotation isKindOfClass:[MGLMultiPolyline class]]
@@ -1745,6 +1752,7 @@ public:
             context.annotation = annotation;
             context.imageReuseIdentifier = annotationImage.reuseIdentifier;
             _annotationContextsByAnnotationTag[annotationTag] = context;
+            _annotationTagsByAnnotation[annotation] = annotationTag;
 
             if ([annotation isKindOfClass:[NSObject class]]) {
                 NSAssert(![annotation isKindOfClass:[MGLMultiPoint class]], @"Point annotation should not be MGLMultiPoint.");
@@ -1831,6 +1839,7 @@ public:
         }
 
         _annotationContextsByAnnotationTag.erase(annotationTag);
+        _annotationTagsByAnnotation.erase(annotation);
 
         if ([annotation isKindOfClass:[NSObject class]] &&
             ![annotation isKindOfClass:[MGLMultiPoint class]]) {