[ios] Updated MGLScaleBar to use rendered UIImages instead of MGLScaleBarLabel (#11921)

3 files changed, 273 insertions, 63 deletions

diff --git a/platform/ios/CHANGELOG.md b/platform/ios/CHANGELOG.md
index 7c8181a65a..1cf5bf1e66 100644
--- a/platform/ios/CHANGELOG.md
+++ b/platform/ios/CHANGELOG.md
@@ -19,6 +19,7 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 * Improved application launch performance.
 * Fixed an issue preventing nested key path expressions get parsed accordingly to the spec. ([#11959](https://github.com/mapbox/mapbox-gl-native/pull/11959))
 * Added custom `-hitTest:withEvent:` to `MGLSMCalloutView` to avoid registering taps in transparent areas of the standard annotation callout. ([#11939](https://github.com/mapbox/mapbox-gl-native/pull/11939))
+* Improved performance and memory impact of `MGLScaleBar`. ([#11921](https://github.com/mapbox/mapbox-gl-native/pull/11921))
 
 ## 4.0.1 - May 14, 2018
 
diff --git a/platform/ios/app/MBXViewController.m b/platform/ios/app/MBXViewController.m
index 0cb6c73d31..a1479b4538 100644
--- a/platform/ios/app/MBXViewController.m
+++ b/platform/ios/app/MBXViewController.m
@@ -91,6 +91,7 @@ typedef NS_ENUM(NSInteger, MBXSettingsRuntimeStylingRows) {
 typedef NS_ENUM(NSInteger, MBXSettingsMiscellaneousRows) {
     MBXSettingsMiscellaneousShowReuseQueueStats = 0,
     MBXSettingsMiscellaneousWorldTour,
+    MBXSettingsMiscellaneousRandomTour,
     MBXSettingsMiscellaneousShowZoomLevel,
     MBXSettingsMiscellaneousScrollView,
     MBXSettingsMiscellaneousToggleTwoMaps,
@@ -101,6 +102,65 @@ typedef NS_ENUM(NSInteger, MBXSettingsMiscellaneousRows) {
     MBXSettingsMiscellaneousDeleteLogFile,
 };
 
+// Utility methods
+CLLocationCoordinate2D coordinateCentered(CLLocationCoordinate2D origin, CLLocationDegrees bearing, CLLocationDistance distance) {
+
+    // Convert to radians
+    double multiplier      = M_PI / 180.0;
+    double sourceLatitude  = multiplier * origin.latitude;
+    double sourceLongitude = multiplier * origin.longitude;
+    bearing *= multiplier;
+    distance /= 6378137.0;
+
+    // Pulled from MGLRadianCoordinateAtDistanceFacingDirection:
+    double latitude = asin((sin(sourceLatitude) * cos(distance)) +
+                           (cos(sourceLatitude) * sin(distance) * cos(bearing)));
+
+    double longitude = sourceLongitude + atan2((sin(bearing) * sin(distance) * cos(sourceLatitude)),
+                                               cos(distance) - (sin(sourceLatitude) * sin(latitude)));
+
+    CLLocationCoordinate2D result;
+    result.latitude  = fmin(85.0, fmax(-85.0, (latitude / multiplier)));
+    result.longitude = longitude / multiplier;
+    return result;
+}
+
+CLLocationCoordinate2D randomWorldCoordinate() {
+
+    static const struct {
+        CLLocationCoordinate2D coordinate;
+        CLLocationDistance radius;
+    } landmasses[] = {
+        // Rough land masses
+        {{ 38.328531,   94.778736 },    4100000 },  // Asia
+        {{ 1.477244,    18.138111 },    4100000 },  // Africa
+        {{ 52.310059,   22.295425 },    2000000 },  // Europe
+        {{ 42.344216,   -96.532700 },   3000000 },  // N America
+        {{ -11.537273,  -57.035181 },   2220000 },  // S America
+        {{ -20.997030,  134.660541 },   2220000 },  // Australia
+
+        // A few cities
+        {{ 51.504787,   -0.106977 },    33000 },    // London
+        {{ 37.740186,   -122.437086 },  8500 },     // SF
+        {{ 52.509978,   13.406510 },    12000 },    // Berlin
+        {{ 12.966246,   77.586505 },    19000 }     // Bengaluru
+    };
+
+    NSInteger index                   = drand48() * (sizeof(landmasses)/sizeof(landmasses[0]));
+    CLLocationCoordinate2D coordinate = landmasses[index].coordinate;
+    CLLocationDistance radius         = landmasses[index].radius;
+
+    // Now create a world coord
+    CLLocationDegrees heading          = drand48()*360.0;
+    CLLocationDistance distance        = drand48()*radius;
+    CLLocationCoordinate2D newLocation = coordinateCentered(coordinate, heading, distance);
+    return newLocation;
+}
+
+
+
+
+
 @interface MBXDroppedPinAnnotation : MGLPointAnnotation
 @end
 
@@ -136,13 +196,11 @@ typedef NS_ENUM(NSInteger, MBXSettingsMiscellaneousRows) {
 @property (nonatomic) BOOL reuseQueueStatsEnabled;
 @property (nonatomic) BOOL showZoomLevelEnabled;
 @property (nonatomic) BOOL shouldLimitCameraChanges;
-
+@property (nonatomic) BOOL randomWalk;
 @end
 
 @interface MGLMapView (MBXViewController)
-
 @property (nonatomic) NSDictionary *annotationViewReuseQueueByIdentifier;
-
 @end
 
 @implementation MBXViewController
@@ -277,6 +335,8 @@ typedef NS_ENUM(NSInteger, MBXSettingsMiscellaneousRows) {
 
 - (IBAction)showSettings:(__unused id)sender
 {
+    self.randomWalk = NO;
+
     UITableViewController *settingsViewController = [[UITableViewController alloc] initWithStyle:UITableViewStyleGrouped];
     settingsViewController.tableView.delegate = self;
     settingsViewController.tableView.dataSource = self;
@@ -377,6 +437,7 @@ typedef NS_ENUM(NSInteger, MBXSettingsMiscellaneousRows) {
             [settingsTitles addObjectsFromArray:@[
                 [NSString stringWithFormat:@"%@ Reuse Queue Stats", (_reuseQueueStatsEnabled ? @"Hide" :@"Show")],
                 @"Start World Tour",
+                @"Random Tour",
                 [NSString stringWithFormat:@"%@ Zoom/Pitch/Direction Label", (_showZoomLevelEnabled ? @"Hide" :@"Show")],
                 @"Embedded Map View",
                 [NSString stringWithFormat:@"%@ Second Map", ([self.view viewWithTag:2] == nil ? @"Show" : @"Hide")],
@@ -580,6 +641,10 @@ typedef NS_ENUM(NSInteger, MBXSettingsMiscellaneousRows) {
                 case MBXSettingsMiscellaneousWorldTour:
                     [self startWorldTour];
                     break;
+                case MBXSettingsMiscellaneousRandomTour:
+                    [self randomWorldTour];
+                    break;
+
                 case MBXSettingsMiscellaneousPrintLogFile:
                     [self printTelemetryLogFile];
                     break;
@@ -1681,6 +1746,75 @@ typedef NS_ENUM(NSInteger, MBXSettingsMiscellaneousRows) {
     return filePath;
 }
 
+#pragma mark - Random World Tour
+
+- (void)addAnnotations:(NSInteger)numAnnotations aroundCoordinate:(CLLocationCoordinate2D)coordinate radius:(CLLocationDistance)radius {
+    NSMutableArray *annotations = [[NSMutableArray alloc] initWithCapacity:numAnnotations];
+    for (NSInteger i = 0; i<numAnnotations; i++) {
+
+        CLLocationDegrees heading          = drand48()*360.0;
+        CLLocationDistance distance        = drand48()*radius;
+        CLLocationCoordinate2D newLocation = coordinateCentered(coordinate, heading, distance);
+
+        MBXDroppedPinAnnotation *annotation = [[MBXDroppedPinAnnotation alloc] init];
+        annotation.coordinate = newLocation;
+        [annotations addObject:annotation];
+    }
+    [self.mapView addAnnotations:annotations];
+}
+
+- (void)randomWorldTour {
+    // Consistent initial conditions (consider setting these by test params)
+    srand48(0);
+    [self.mapView removeAnnotations:self.mapView.annotations];
+    [self.mapView setCenterCoordinate:CLLocationCoordinate2DMake(31, -100) zoomLevel:3 animated:NO];
+
+    [self randomWorldTourInternal];
+}
+
+- (void)randomWorldTourInternal {
+
+    self.randomWalk = YES;
+
+    // Remove all annotations
+    NSTimeInterval duration = 16.0;
+    __weak MBXViewController *weakSelf = self;
+
+    // Remove old annotations, half-way through the flight.
+    NSArray *annotationsToRemove = [self.mapView.annotations copy];
+    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(duration * 0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
+        [weakSelf.mapView removeAnnotations:annotationsToRemove];
+    });
+
+    MBXDroppedPinAnnotation *annotation = [[MBXDroppedPinAnnotation alloc] init];
+    annotation.coordinate = randomWorldCoordinate();
+    [self.mapView addAnnotation:annotation];
+
+    // Add annotations around that coord
+    [self addAnnotations:50 aroundCoordinate:annotation.coordinate radius:100000.0]; // 100km
+
+    MGLMapCamera *camera = [MGLMapCamera cameraLookingAtCenterCoordinate:annotation.coordinate
+                                                            fromDistance:10000.0
+                                                                   pitch:drand48()*60.0
+                                                                 heading:drand48()*360];
+    [self.mapView flyToCamera:camera
+                 withDuration:duration
+                 peakAltitude:2000000.0
+            completionHandler:^{
+                // This completion handler is currently called BEFORE the
+                // region did change delegate method, and we don't have a "reason"
+                // so we can't tell if the motion was cancelled. We use the delegate
+                // for that, and set self.randomWalk. But since we want a delay
+                // anyway, we can just check later. Not ideal though..
+                dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
+                    MBXViewController *strongSelf = weakSelf;
+                    if (strongSelf.randomWalk) {
+                        [strongSelf randomWorldTourInternal];
+                    }
+                });
+            }];
+}
+
 #pragma mark - User Actions
 
 - (IBAction)handleLongPress:(UILongPressGestureRecognizer *)longPress
@@ -2033,6 +2167,10 @@ typedef NS_ENUM(NSInteger, MBXSettingsMiscellaneousRows) {
 
 - (void)mapView:(MGLMapView *)mapView regionDidChangeWithReason:(MGLCameraChangeReason)reason animated:(BOOL)animated
 {
+    if (reason != MGLCameraChangeReasonProgrammatic) {
+        self.randomWalk = NO;
+    }
+
     [self updateHUD];
 }
 
diff --git a/platform/ios/src/MGLScaleBar.mm b/platform/ios/src/MGLScaleBar.mm
index a2fc24c75c..d69fb3e852 100644
--- a/platform/ios/src/MGLScaleBar.mm
+++ b/platform/ios/src/MGLScaleBar.mm
@@ -75,7 +75,7 @@ static const MGLRow MGLImperialTable[] ={
 @class MGLScaleBarLabel;
 
 @interface MGLScaleBar()
-@property (nonatomic) NSArray<MGLScaleBarLabel *> *labels;
+@property (nonatomic) NSArray<UIView *> *labelViews;
 @property (nonatomic) NSArray<UIView *> *bars;
 @property (nonatomic) UIView *containerView;
 @property (nonatomic) MGLDistanceFormatter *formatter;
@@ -84,6 +84,10 @@ static const MGLRow MGLImperialTable[] ={
 @property (nonatomic) UIColor *secondaryColor;
 @property (nonatomic) CALayer *borderLayer;
 @property (nonatomic, assign) CGFloat borderWidth;
+@property (nonatomic) NSCache* labelImageCache;
+@property (nonatomic) MGLScaleBarLabel* prototypeLabel;
+
+
 @end
 
 static const CGFloat MGLBarHeight = 4;
@@ -152,6 +156,29 @@ static const CGFloat MGLFeetPerMeter = 3.28084;
     [_containerView.layer addSublayer:_borderLayer];
     
     _formatter = [[MGLDistanceFormatter alloc] init];
+
+    // Image labels are now images
+    _labelImageCache              = [[NSCache alloc] init];
+    _prototypeLabel               = [[MGLScaleBarLabel alloc] init];
+    _prototypeLabel.font          = [UIFont systemFontOfSize:8 weight:UIFontWeightMedium];
+    _prototypeLabel.clipsToBounds = NO;
+
+    NSUInteger numberOfLabels = 4;
+    NSMutableArray *labelViews = [NSMutableArray arrayWithCapacity:numberOfLabels];
+
+    for (NSUInteger i = 0; i < numberOfLabels; i++) {
+        UIView *view = [[UIView alloc] init];
+        view.bounds        = CGRectZero;
+        view.clipsToBounds = NO;
+        view.contentMode   = UIViewContentModeCenter;
+        view.hidden        = YES;
+        [labelViews addObject:view];
+        [self addSubview:view];
+    }
+    _labelViews = [labelViews copy];
+
+    // Zero is a special case (no formatting)
+    [self addZeroLabel];
 }
 
 #pragma mark - Dimensions
@@ -190,21 +217,31 @@ static const CGFloat MGLFeetPerMeter = 3.28084;
     CLLocationDistance maximumDistance = [self maximumWidth] * [self unitsPerPoint];
     
     BOOL useMetric = [self usesMetricSystem];
-    MGLRow row = useMetric ? MGLMetricTable[0] : MGLImperialTable[0];
-    NSUInteger count = useMetric
-    ? sizeof(MGLMetricTable) / sizeof(MGLMetricTable[0])
-    : sizeof(MGLImperialTable) / sizeof(MGLImperialTable[0]);
-    
-    for (NSUInteger i = 0; i < count; i++) {
-        CLLocationDistance distance = useMetric ? MGLMetricTable[i].distance : MGLImperialTable[i].distance;
-        if (distance <= maximumDistance) {
-            row = useMetric ? MGLMetricTable[i] : MGLImperialTable[i];
-        } else {
-            break;
+
+    const MGLRow *row;
+    const MGLRow *table;
+    NSUInteger count;
+
+    if (useMetric) {
+        row = table = MGLMetricTable;
+        count = sizeof(MGLMetricTable) / sizeof(MGLMetricTable[0]);
+    }
+    else {
+        row = table = MGLImperialTable;
+        count = sizeof(MGLImperialTable) / sizeof(MGLImperialTable[0]);
+    }
+
+    while (row < table + count) {
+        if (row->distance > maximumDistance) {
+            // use the previous row
+            NSAssert(row != table, @"");
+            return *(row - 1);
         }
+        ++row;
     }
-    
-    return row;
+
+    // Didn't find it, just return the first.
+    return *table;
 }
 
 #pragma mark - Setters
@@ -255,9 +292,9 @@ static const CGFloat MGLFeetPerMeter = 3.28084;
     
     _row = row;
     [_bars makeObjectsPerformSelector:@selector(removeFromSuperview)];
-    [_labels makeObjectsPerformSelector:@selector(removeFromSuperview)];
     _bars = nil;
-    _labels = nil;
+
+    [self updateLabels];
 }
 
 #pragma mark - Views
@@ -275,61 +312,91 @@ static const CGFloat MGLFeetPerMeter = 3.28084;
     return _bars;
 }
 
-- (NSArray<UILabel *> *)labels {
-    if (!_labels) {
-        NSDecimalNumber *zeroNumber = [NSDecimalNumber decimalNumberWithString:@"0"];
-        NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
-        NSMutableArray *labels = [NSMutableArray array];
-        
-        for (NSUInteger i = 0; i <= self.row.numberOfBars; i++) {
-            UILabel *label = [[MGLScaleBarLabel alloc] init];
-            label.font = [UIFont systemFontOfSize:8 weight:UIFontWeightMedium];
-            label.text = [formatter stringFromNumber:zeroNumber];
-            label.clipsToBounds = NO;
-            [label setNeedsDisplay];
-            [label sizeToFit];
-            [labels addObject:label];
-            [self addSubview:label];
-        }
-        _labels = labels;
+#pragma mark - Labels
+
+- (void)addZeroLabel {
+    NSDecimalNumber *zeroNumber = [NSDecimalNumber decimalNumberWithString:@"0"];
+    NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
+    NSString *text = [formatter stringFromNumber:zeroNumber];
+
+    UIImage* image = [self imageForLabelText:text];
+    [self.labelImageCache setObject:image forKey:@(0)];
+}
+
+- (UIImage*)imageForLabelText:(NSString*)text {
+    self.prototypeLabel.text = text;
+    [self.prototypeLabel setNeedsDisplay];
+    [self.prototypeLabel sizeToFit];
+
+    // Now render
+    UIGraphicsBeginImageContextWithOptions(self.prototypeLabel.bounds.size, NO, 0.0);
+    [self.prototypeLabel.layer renderInContext: UIGraphicsGetCurrentContext()];
+    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
+    UIGraphicsEndImageContext();
+    return image;
+}
+
+- (UIImage*)cachedLabelImageForDistance:(CLLocationDistance)barDistance {
+    // Make a slightly nicer key, rather than something that's a double.
+    NSUInteger floorDist = (NSUInteger)(barDistance*100);
+
+    NSNumber *key = @(floorDist);
+    UIImage *cachedImage = [self.labelImageCache objectForKey:key];
+
+    if (cachedImage) {
+        return cachedImage;
+    }
+
+    // Calc it
+    NSString *text = [self.formatter stringFromDistance:barDistance];
+    UIImage *image = [self imageForLabelText:text];
+
+    [self.labelImageCache setObject:image forKey:key];
+
+    return image;
+}
+
+- (void)updateLabels {
+    NSEnumerator<UIView*> *viewEnumerator = [self.labelViews objectEnumerator];
+    NSInteger i = 0;
+    CLLocationDistance multiplier = (self.row.distance / self.row.numberOfBars);
+
+    if (![self usesMetricSystem]) {
+        multiplier /= MGLFeetPerMeter;
+    }
+
+    for (; i <= self.row.numberOfBars; i++) {
+        UIView *labelView = [viewEnumerator nextObject];
+        labelView.hidden = NO;
+
+        CLLocationDistance barDistance = multiplier * i;
+        UIImage *image = [self cachedLabelImageForDistance:barDistance];
+
+        labelView.layer.contents      = (id)image.CGImage;
+        labelView.layer.contentsScale = image.scale;
+    }
+
+    // Hide the rest.
+    for (; i < self.labelViews.count; i++) {
+        UIView *labelView = [viewEnumerator nextObject];
+        labelView.hidden = YES;
     }
-    return _labels;
 }
 
 #pragma mark - Layout
 
 - (void)layoutSubviews {
     [super layoutSubviews];
-    
+
     if (!self.row.numberOfBars) {
         // Current distance is not within allowed range
         return;
     }
-    
-    [self updateLabels];
+
     [self layoutBars];
     [self layoutLabels];
 }
 
-- (void)updateLabels {
-    NSArray *labels = [self.labels subarrayWithRange:NSMakeRange(1, self.labels.count-1)];
-    BOOL useMetric = [self usesMetricSystem];
-    NSUInteger i = 0;
-    
-    for (MGLScaleBarLabel *label in labels) {
-        CLLocationDistance barDistance = (self.row.distance / self.row.numberOfBars) * (i + 1);
-        
-        if (!useMetric) {
-            barDistance /= MGLFeetPerMeter;
-        }
-        
-        label.text = [self.formatter stringFromDistance:barDistance];
-        [label setNeedsDisplay];
-        [label sizeToFit];
-        i++;
-    }
-}
-
 - (void)layoutBars {
     CGFloat barWidth = round((CGRectGetWidth(self.bounds) - self.borderWidth * 2.0f) / self.bars.count);
     
@@ -357,11 +424,15 @@ static const CGFloat MGLFeetPerMeter = 3.28084;
     CGFloat barWidth = round(self.bounds.size.width / self.bars.count);
     BOOL RTL = [self usesRightToLeftLayout];
     NSUInteger i = RTL ? self.bars.count : 0;
-    for (MGLScaleBarLabel *label in self.labels) {
+    for (UIView *label in self.labelViews) {
         CGFloat xPosition = round(barWidth * i - CGRectGetMidX(label.bounds) + self.borderWidth);
-        label.frame = CGRectMake(xPosition, 0,
-                                 CGRectGetWidth(label.bounds),
-                                 CGRectGetHeight(label.bounds));
+        CGFloat yPosition = round(0.5 * (CGRectGetMaxY(self.bounds) - MGLBarHeight));
+
+        CGRect frame = label.frame;
+        frame.origin.x = xPosition;
+        frame.origin.y = yPosition;
+        label.frame = frame;
+
         i = RTL ? i-1 : i+1;
     }
 }