问题:

How can I draw such a conical gradient in iOS using Core Graphics / Quartz 2D API?

Conical Gradient Sample http://ods.com.ua/win/eng/other/gimpdoc-html/painta27.gif

回答1:

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

回答2:

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

It's not tested for performance, so beware.

回答3:

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).

回答4:

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.