[ios] Avoid drawing view annotations across pixel boundaries

platform/darwin/src/MGLGeometry.mm

@@ -4,6 +4,10 @@
 
 #import <mbgl/util/projection.hpp>
 
+#if !TARGET_OS_IPHONE && !TARGET_OS_SIMULATOR
+#import <Cocoa/Cocoa.h>
+#endif
+
 /** Vertical field of view, measured in degrees, for determining the altitude
     of the viewpoint.
 
@@ -57,3 +61,12 @@ CLLocationDistance MGLAltitudeForZoomLevel(double zoomLevel, CGFloat pitch, CLLo
     CGFloat mapPixelWidthAtZoom = std::cos(MGLRadiansFromDegrees(latitude)) * mbgl::util::M2PI * mbgl::util::EARTH_RADIUS_M / metersPerPixel;
     return ::log2(mapPixelWidthAtZoom / mbgl::util::tileSize);
 }
+
+CGPoint MGLPointRounded(CGPoint point) {
+#if TARGET_OS_IPHONE || TARGET_OS_SIMULATOR
+    CGFloat scaleFactor = [UIScreen instancesRespondToSelector:@selector(nativeScale)] ? [UIScreen mainScreen].nativeScale : [UIScreen mainScreen].scale;
+#elif TARGET_OS_MAC
+    CGFloat scaleFactor = [NSScreen mainScreen].backingScaleFactor;
+#endif
+    return CGPointMake(round(point.x * scaleFactor) / scaleFactor, round(point.y * scaleFactor) / scaleFactor);
+}

platform/darwin/src/MGLGeometry_Private.h

@@ -138,3 +138,5 @@ NS_INLINE MGLRadianCoordinate2D MGLRadianCoordinateAtDistanceFacingDirection(MGL
                                                          cos(distance) - sin(coordinate.latitude) * sin(otherLatitude));
     return MGLRadianCoordinate2DMake(otherLatitude, otherLongitude);
 }
+
+CGPoint MGLPointRounded(CGPoint point);

platform/ios/CHANGELOG.md

@@ -31,6 +31,7 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 * Selecting an annotation no longer sets the user tracking mode to `MGLUserTrackingModeNone`. ([#10094](https://github.com/mapbox/mapbox-gl-native/pull/10094))
 * Added `-[MGLMapView cameraThatFitsShape:direction:edgePadding:]` to get a camera with zoom level and center coordinate computed to fit a shape. ([#10107](https://github.com/mapbox/mapbox-gl-native/pull/10107))
 * Added support selection of shape and polyline annotations.([#9984](https://github.com/mapbox/mapbox-gl-native/pull/9984))
+* Fixed an issue where view annotations could be slightly misaligned. View annotation placement is now rounded to the nearest pixel. ([#10219](https://github.com/mapbox/mapbox-gl-native/pull/10219))
 
 ### Other changes
 

platform/ios/src/MGLFaux3DUserLocationAnnotationView.m

@@ -10,7 +10,7 @@
 const CGFloat MGLUserLocationAnnotationHaloSize = 115.0;
 
 const CGFloat MGLUserLocationAnnotationPuckSize = 45.0;
-const CGFloat MGLUserLocationAnnotationArrowSize = MGLUserLocationAnnotationPuckSize * 0.6;
+const CGFloat MGLUserLocationAnnotationArrowSize = MGLUserLocationAnnotationPuckSize * 0.5;
 
 const CGFloat MGLUserLocationHeadingUpdateThreshold = 0.01;
 
@@ -175,12 +175,16 @@ - (void)drawPuck
         _puckArrow = [CAShapeLayer layer];
         _puckArrow.path = [[self puckArrow] CGPath];
         _puckArrow.fillColor = [self.mapView.tintColor CGColor];
-        _puckArrow.bounds = CGRectMake(0, 0, MGLUserLocationAnnotationArrowSize, MGLUserLocationAnnotationArrowSize);
-        _puckArrow.position = CGPointMake(super.bounds.size.width / 2.0, super.bounds.size.height / 2.0);
+        _puckArrow.bounds = CGRectMake(0, 0, round(MGLUserLocationAnnotationArrowSize), round(MGLUserLocationAnnotationArrowSize));
+        _puckArrow.position = CGPointMake(CGRectGetMidX(super.bounds), CGRectGetMidY(super.bounds));
         _puckArrow.shouldRasterize = YES;
         _puckArrow.rasterizationScale = [UIScreen mainScreen].scale;
         _puckArrow.drawsAsynchronously = YES;
 
+        _puckArrow.lineJoin = @"round";
+        _puckArrow.lineWidth = 1.f;
+        _puckArrow.strokeColor = _puckArrow.fillColor;
+
         [self.layer addSublayer:_puckArrow];
     }
     if (self.userLocation.location.course >= 0)
@@ -302,7 +306,7 @@ - (void)drawDot
             [CATransaction setDisableActions:shouldDisableActions];
 
             _accuracyRingLayer.bounds = CGRectMake(0, 0, accuracyRingSize, accuracyRingSize);
-            _accuracyRingLayer.cornerRadius = accuracyRingSize / 2;
+            _accuracyRingLayer.cornerRadius = accuracyRingSize / 2.0;
 
             // match the halo to the accuracy ring
             _haloLayer.bounds = _accuracyRingLayer.bounds;
@@ -431,9 +435,11 @@ - (void)drawDot
 
 - (CALayer *)circleLayerWithSize:(CGFloat)layerSize
 {
+    layerSize = round(layerSize);
+
     CALayer *circleLayer = [CALayer layer];
     circleLayer.bounds = CGRectMake(0, 0, layerSize, layerSize);
-    circleLayer.position = CGPointMake(super.bounds.size.width / 2.0, super.bounds.size.height / 2.0);
+    circleLayer.position = CGPointMake(CGRectGetMidX(super.bounds), CGRectGetMidY(super.bounds));
     circleLayer.cornerRadius = layerSize / 2.0;
     circleLayer.shouldRasterize = YES;
     circleLayer.rasterizationScale = [UIScreen mainScreen].scale;
@@ -456,7 +462,7 @@ - (CAAnimationGroup *)loopingAnimationGroupWithDuration:(CGFloat)animationDurati
 - (CGFloat)calculateAccuracyRingSize
 {
     // diameter in screen points
-    return self.userLocation.location.horizontalAccuracy / [self.mapView metersPerPointAtLatitude:self.userLocation.coordinate.latitude] * 2.0;
+    return round(self.userLocation.location.horizontalAccuracy / [self.mapView metersPerPointAtLatitude:self.userLocation.coordinate.latitude] * 2.0);
 }
 
 @end

platform/ios/src/MGLMapView.mm

@@ -3379,7 +3379,7 @@ - (void)addAnnotations:(NS_ARRAY_OF(id <MGLAnnotation>) *)annotations
                 {
                     annotationViewsForAnnotation[annotationValue] = annotationView;
                     annotationView.annotation = annotation;
-                    annotationView.center = [self convertCoordinate:annotation.coordinate toPointToView:self];
+                    annotationView.center = MGLPointRounded([self convertCoordinate:annotation.coordinate toPointToView:self]);
                     [newAnnotationViews addObject:annotationView];
 
                     MGLAnnotationImage *annotationImage = self.invisibleAnnotationImage;
@@ -3805,7 +3805,7 @@ - (MGLAnnotationTag)annotationTagAtPoint:(CGPoint)point persistingResults:(BOOL)
                         return true;
                     }
 
-                    CGPoint calloutAnchorPoint = [self convertCoordinate:annotation.coordinate toPointToView:self];
+                    CGPoint calloutAnchorPoint = MGLPointRounded([self convertCoordinate:annotation.coordinate toPointToView:self]);
                     CGRect frame = CGRectInset({ calloutAnchorPoint, CGSizeZero }, -CGRectGetWidth(annotationView.frame) / 2, -CGRectGetHeight(annotationView.frame) / 2);
                     annotationRect = UIEdgeInsetsInsetRect(frame, annotationView.alignmentRectInsets);
                 }
@@ -4143,7 +4143,7 @@ - (CGRect)positioningRectForCalloutForAnnotationWithTag:(MGLAnnotationTag)annota
 /// image centered at the given coordinate.
 - (CGRect)frameOfImage:(UIImage *)image centeredAtCoordinate:(CLLocationCoordinate2D)coordinate
 {
-    CGPoint calloutAnchorPoint = [self convertCoordinate:coordinate toPointToView:self];
+    CGPoint calloutAnchorPoint = MGLPointRounded([self convertCoordinate:coordinate toPointToView:self]);
     CGRect frame = CGRectInset({ calloutAnchorPoint, CGSizeZero }, -image.size.width / 2, -image.size.height / 2);
     return UIEdgeInsetsInsetRect(frame, image.alignmentRectInsets);
 }
@@ -4582,7 +4582,6 @@ - (void)setShowsUserHeadingIndicator:(BOOL)showsUserHeadingIndicator
     if (_showsUserHeadingIndicator)
     {
         self.showsUserLocation = YES;
-
     }
     [self validateUserHeadingUpdating];
 }
@@ -5288,7 +5287,7 @@ - (void)updateAnnotationViews
 
         if (annotationView)
         {
-            annotationView.center = [self convertCoordinate:annotationContext.annotation.coordinate toPointToView:self];
+            annotationView.center = MGLPointRounded([self convertCoordinate:annotationContext.annotation.coordinate toPointToView:self]);
         }
     }
 
@@ -5406,7 +5405,7 @@ - (void)updateUserLocationAnnotationViewAnimatedWithDuration:(NSTimeInterval)dur
     }
     else
     {
-        userPoint = [self convertCoordinate:self.userLocation.coordinate toPointToView:self];
+        userPoint = MGLPointRounded([self convertCoordinate:self.userLocation.coordinate toPointToView:self]);
     }
 
     if ( ! annotationView.superview)

platform/ios/src/MGLScaleBar.mm

@@ -334,7 +334,7 @@ - (void)updateLabels {
 }
 
 - (void)layoutBars {
-    CGFloat barWidth = (CGRectGetWidth(self.bounds) - self.borderWidth * 2.0f) / self.bars.count;
+    CGFloat barWidth = round((CGRectGetWidth(self.bounds) - self.borderWidth * 2.0f) / self.bars.count);
 
     NSUInteger i = 0;
     for (UIView *bar in self.bars) {
@@ -357,11 +357,11 @@ - (void)layoutBars {
 }
 
 - (void)layoutLabels {
-    CGFloat barWidth = self.bounds.size.width / self.bars.count;
+    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) {
-        CGFloat xPosition = barWidth * i - CGRectGetMidX(label.bounds) + self.borderWidth;
+        CGFloat xPosition = round(barWidth * i - CGRectGetMidX(label.bounds) + self.borderWidth);
         label.frame = CGRectMake(xPosition, 0,
                                  CGRectGetWidth(label.bounds),
                                  CGRectGetHeight(label.bounds));