A CoreImage filter used to composite the layer and the content behind it. Animatable.
The default value of this property is nil, which causes the layer to use source-over compositing. Although you can use any Core Image filter as a layer's compositing filter, for best results, use those in the CICategoryCompositeOperation category.
In macOS, it is possible to modify the filter’s parameters after attaching it to the layer but you must use the layer’s setValue(_:forKeyPath:) method to do so. For example, to change the inputRadius parameter of the filter, you could use code similar to the following:
Changing the inputs of the CIFilter object directly after it is attached to the layer causes undefined behavior.
Listing 2 shows how to create two overlapping text layers, background and foreground. Addition compositing is used to composite the foreground over the background.
Figure 1 shows the result: the identical background colors of the two layers are added together so that a brighter gray is produced where the layers overlap.