CALayer renderInContext method ignores maskedCorners property

Number:rdar://41414439 Date Originated:June 25 2018
Status:Open Resolved:
Product:iOS + SDK Product Version:iOS 11.0+
Classification:UI/Usability Reproducible:Always
Core Animation

Using CALayer.maskedCorners property to disable masking for some of the corners has no effect over the "snapshot" of the layer rendered using renderInContext method: it still draws the layer hierarchy with all four corners masked.

Steps to Reproduce:
1. Create a simple view hierarchy, with one of the views' layers configured as such:
        layer.masksToBounds = true
        layer.cornerRadius = 20
        layer.maskedCorners = [ .layerMaxXMinYCorner, .layerMinXMaxYCorner ]
2. At some point render the layer of this masked view using CALayer. renderInContext method (via UIGraphicsImageRenderer).

Expected Results:
Produced "snapshot" only has top-right and bottom-left corners rounded, as actually displayed on the screen.

Actual Results:
Produced "snapshot" has all four corners rounded, as if maskedCorners has its default value.

iOS 11.0 and later; reproducible in iOS 12 beta 1.

Any device or simulator.


I think this is the cause of an issue I'm seeing on macOS 10.14.3. When dragging an NSCollectionViewItem a CALayer with two masked corners is displayed with all four masked.

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