CALayer cornerRadius + masksToBounds 10.11 glitch?

Question

I have a 30x30 view which is rounded:

CALayer * layer = self.layer;
layer.backgroundColor = [NSColor redColor].CGColor;
layer.cornerRadius = 10.0f;
layer.masksToBounds = YES;

So far, so good:

Then I add a sublayer, like so:

CALayer * subLayer = [CALayer layer];
subLayer.backgroundColor = [NSColor yellowColor].CGColor;
subLayer.frame = CGRectMake(0.0f, 0.0f, 10.0f, 10.0f);
[layer addSublayer:subLayer];

And I end up with this, which is not what I want!

This is a problem that has only surfaced since my upgrade to El Capitan. In Yosemite the masking worked for the above code. What am I missing?

Update: this issue does not occur when I set layer.shouldRasterize = YES; however I want to keep memory down so I would prefer another solution.

Answer 1

I have found my own solution, using a shape layer + mask instead of cornerRadius:

CALayer * layer = self.layer;
layer.backgroundColor = [NSColor redColor].CGColor;
//
// code to replace layer.cornerRadius:
CAShapeLayer * shapeLayer = [CAShapeLayer layer];
float const r = 10.0f;
float const w = self.bounds.size.width;
float const h = self.bounds.size.height;
CGMutablePathRef path = CGPathCreateMutable();
CGPathMoveToPoint(path, NULL, r, 0.0f);
CGPathAddArcToPoint(path, NULL, w, 0.0f, w, r, r);
CGPathAddArcToPoint(path, NULL, w, h, w - r, h, r);
CGPathAddArcToPoint(path, NULL, 0.0f, h, 0.0f, h - r, r);
CGPathAddArcToPoint(path, NULL, 0.0f, 0.0f, r, 0.0f, r);
CGPathCloseSubpath ( path );
shapeLayer.path = path;
CGPathRelease(path);
self.layer.mask = shapeLayer;
//
// add the sublayer
CALayer * subLayer = [CALayer layer];
subLayer.backgroundColor = [NSColor yellowColor].CGColor;
subLayer.frame = CGRectMake(0.0f, 0.0f, 10.0f, 10.0f);
[layer addSublayer:subLayer];

Works as intended:

(Of course, if anyone has a more elegant fix, I'd love to see it!)