How to make a conical gradient in iOS using Core Graphics / Quartz 2D?

How can I draw such a conical gradient in iOS using Core Graphics / Quartz 2D API?开发者_如何学Go

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If anyone is still looking for a solution, Apple finally introduced .conic gradient type in iOS 12. Perfect for masking to create circular progress bar with gradient.

Example:

let gradientLayer = CAGradientLayer()
gradientLayer.startPoint = CGPoint(x: 0.5, y: 0.5)
gradientLayer.endPoint = CGPoint(x: 0.5, y: 0)
gradientLayer.type = .conic
gradientLayer.colors = [UIColor.red.cgColor, UIColor.orange.cgColor, UIColor.green.cgColor]
gradientLayer.frame = bounds

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Recently I've made a custom CALayer class for this: AngleGradientLayer

It's not tested for performance, so beware.

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I wanted pure Swift solution for this, and it was also kind of a challenging task for me.

At the end, I wrote AEConicalGradient which does that with interesting approach (by using a circle and drawing lines of different colors to the center).

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There is no Quartz function for this style of gradient. Unless you're ready to dig into mathematics behind it, I'd suggest you use pre-made images for this. It's not a problem if you need it only for opacity mask.