swift - Draw iOS 7-style squircle programmatically

Question

I'm trying to find a way to draw a iOS 7-style icon 'squircle' shape programmatically, using core graphics. I'm not asking how to draw a rounded rectangle. A squircle is a superellipse:

which is slightly different than a regular rounded rectangle:

It's exact formula is readily available. However, I can't figure out how to draw this using, for example, a CGPath, let alone fill it, and be able to resize it rather easily. All this while being entirely exact with the formula.

Answer 1

in iOS 13/ Xcode 11 you can now use CALayerCornerCurve

Example

yourLayer.cornerCurve = CALayerCornerCurve.continuous

source: https://developer.apple.com/documentation/quartzcore/calayercornercurve