Add support for inverted matte layers #1712
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| // We can invert the mask layer by having a large solid black layer with the | ||
| // given mask layer subtracted out using the `xor` blend mode. When applied to the | ||
| // layer being masked, this creates an inverted mask where only areas _outside_ | ||
| // of the mask layer are visible. | ||
| // https://developer.apple.com/documentation/coregraphics/cgblendmode/xor |
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This is awesome, can't wait to try it out. Thanks for all the hard work! |
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This PR adds support for inverted matte layers to the Core Animation rendering engine. Fixes #1655.
Last time I looked in to this I couldn't figure out how to create an inverted mask from an arbitrary
CALayer. All of the discussion online (example) said to render the layers into an image and then use Core Image to apply the inverted mask. This is how the Main Thread rendering engine works, which is a source of performance issues. That approach doesn't work for the Core Animation engine, since it requires manually re-rendering the image every frame.We recently added support for blend modes (#1585), which seemed promising for something like this. The documentation for these is woefully inadequate, it even says "This property is not supported on layers in iOS" which is just no longer the case. I tried a bunch of the blend modes listed on this page and found that
xordoes exactly what we need here 🎉