1 files changed, 104 insertions, 0 deletions
diff --git a/platform/ios/src/MGLUserLocationHeadingBeamLayer.m b/platform/ios/src/MGLUserLocationHeadingBeamLayer.m
new file mode 100644
index 0000000000..efe7e4db93
--- /dev/null
+++ b/platform/ios/src/MGLUserLocationHeadingBeamLayer.m
@@ -0,0 +1,104 @@
+#import "MGLUserLocationHeadingBeamLayer.h"
+
+#import "MGLFaux3DUserLocationAnnotationView.h"
+#import "MGLGeometry.h"
+
+@implementation MGLUserLocationHeadingBeamLayer
+{
+    CAShapeLayer *_maskLayer;
+}
+
+- (instancetype)initWithUserLocationAnnotationView:(MGLUserLocationAnnotationView *)userLocationView
+{
+    CGFloat size = MGLUserLocationAnnotationHaloSize;
+
+    self = [super init];
+    self.bounds = CGRectMake(0, 0, size, size);
+    self.position = CGPointMake(CGRectGetMidX(userLocationView.bounds), CGRectGetMidY(userLocationView.bounds));
+    self.contents = (__bridge id)[self gradientImageWithTintColor:userLocationView.tintColor.CGColor];
+    self.contentsGravity = kCAGravityBottom;
+    self.contentsScale = UIScreen.mainScreen.scale;
+    self.opacity = 0.4;
+    self.shouldRasterize = YES;
+    self.rasterizationScale = UIScreen.mainScreen.scale;
+    self.drawsAsynchronously = YES;
+
+    _maskLayer = [CAShapeLayer layer];
+    _maskLayer.frame = self.bounds;
+    _maskLayer.path = [self clippingMaskForAccuracy:0];
+    self.mask = _maskLayer;
+
+    return self;
+}
+
+- (void)updateHeadingAccuracy:(CLLocationDirection)accuracy
+{
+    // recalculate the clipping mask based on updated accuracy
+    _maskLayer.path = [self clippingMaskForAccuracy:accuracy];
+}
+
+- (void)updateTintColor:(CGColorRef)color
+{
+    // redraw the raw tinted gradient
+    self.contents = (__bridge id)[self gradientImageWithTintColor:color];
+}
+
+- (CGImageRef)gradientImageWithTintColor:(CGColorRef)tintColor
+{
+    UIImage *image;
+
+    CGFloat haloRadius = MGLUserLocationAnnotationHaloSize / 2.0;
+
+    UIGraphicsBeginImageContextWithOptions(CGSizeMake(MGLUserLocationAnnotationHaloSize, haloRadius), NO, 0);
+
+    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
+    CGContextRef context = UIGraphicsGetCurrentContext();
+
+    // gradient from the tint color to no-alpha tint color
+    CGFloat gradientLocations[] = {0.0, 1.0};
+    CGGradientRef gradient = CGGradientCreateWithColors(
+        colorSpace,
+        (__bridge CFArrayRef)@[(__bridge id)tintColor,
+                               (id)CFBridgingRelease(CGColorCreateCopyWithAlpha(tintColor, 0))],
+        gradientLocations);
+
+    // draw the gradient from the center point to the edge (full halo radius)
+    CGPoint centerPoint = CGPointMake(haloRadius, haloRadius);
+    CGContextDrawRadialGradient(context, gradient,
+                                centerPoint, 0.0,
+                                centerPoint, haloRadius,
+                                kNilOptions);
+
+    image = UIGraphicsGetImageFromCurrentImageContext();
+    UIGraphicsEndImageContext();
+
+    CGGradientRelease(gradient);
+    CGColorSpaceRelease(colorSpace);
+
+    return image.CGImage;
+}
+
+- (CGPathRef)clippingMaskForAccuracy:(CGFloat)accuracy
+{
+    // size the mask using accuracy, but keep within a good display range
+    CGFloat clippingDegrees = 90 - accuracy;
+    clippingDegrees = fmin(clippingDegrees, 70); // most accurate
+    clippingDegrees = fmax(clippingDegrees, 10); // least accurate
+
+    CGRect ovalRect = CGRectMake(0, 0, MGLUserLocationAnnotationHaloSize, MGLUserLocationAnnotationHaloSize);
+    UIBezierPath *ovalPath = UIBezierPath.bezierPath;
+
+    // clip the oval to ± incoming accuracy degrees (converted to radians), from the top
+    [ovalPath addArcWithCenter:CGPointMake(CGRectGetMidX(ovalRect), CGRectGetMidY(ovalRect))
+                        radius:CGRectGetWidth(ovalRect) / 2.0
+                    startAngle:MGLRadiansFromDegrees(-180 + clippingDegrees)
+                      endAngle:MGLRadiansFromDegrees(-clippingDegrees)
+                     clockwise:YES];
+
+    [ovalPath addLineToPoint:CGPointMake(CGRectGetMidX(ovalRect), CGRectGetMidY(ovalRect))];
+    [ovalPath closePath];
+
+    return ovalPath.CGPath;
+}
+
+@end