如何使用CALayer renderInContext并保持透视变换？

Question

How do I use CALayer renderInContext and have the perspective transform (m34) of the layer preserved? It seems like this method assumes an Identity transform. I have tried things like transforming the context, and this is fine for translation, rotation and scaling, but there does not seem to be a way to keep the perspective of the 3D transform.

Maybe a better way to put this question: How do I apply a perspective while drawing to a CGContextRef?

Answer 1

You might want to have a look at the method drawViewHierarchyInRect:afterScreenUpdates: which is offered since iOS 7.0. Applying the method to the view containing the CALayers will keep their 3D transformations.

Sample code:

BOOL opaqueBackground = YES;
UIGraphicsBeginImageContextWithOptions(theViewContainingYourCALayers.bounds.size, !opaqueBackground, 0);
[theViewContainingYourCALayers drawViewHierarchyInRect:theViewContainingYourCALayers.bounds afterScreenUpdates:YES];
[UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

As matt pointed out, relying solely on renderInContext: is not possible since it disregards any transformation other than affine ones.

Late answer but I hope it still helps.