What's the correct code to save a CGLayer as a PNG file?

Question

Please note that this question is about CGLayer (which you typically use to draw offscreen), it is not about CALayer.

In iOS, what's the correct code to save a CGLayer as a PNG file? Thanks!

Again, that's CGLayer, not CALayer.

Note that you CAN NOT use UIGraphicsGetImageFromCurrentImageContext.

(From the documentation, "You can call UIGraphicsGetImageFromCurrentImageContext only when a bitmap-based graphics context is the current graphics context.")

Note that you CAN NOT use renderInContext:. renderInContext: is strictly for CALayers. CGLayers are totally different.

So, how can you actually convert a CGLayer to a PNG image? Or indeed, how to render a CGLayer in to a bitmap in some way (of course you can then easily save as an image).

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------------ LATER .. Ken has completely answered this difficult question. I will paste in a long example code that may help people, in a separate answer below. Thanks again Ken! Amazing!!!!

Answer 1

For iPhone OS, it should be possible to draw a CGLayer on a CGContext and then convert into a UIImage, which can then be encoded into PNG and saved.

CGSize size = CGLayerGetSize(layer);
UIGraphicsBeginImageContext(size);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextDrawLayerAtPoint(ctx, CGPointZero, layer);
UIImage* image = UIGraphicsGetImageFromCurrentImageContext();
NSData* pngData = UIImagePNGRepresentation(image);
[pngData writeToFile:... atomically:YES];
UIGraphicsEndImageContext();

(not tested)