Takes ownership of comp and returns a version of comp that is writable
(i.e. can be modified). Will either return comp right away, or create a
new writable copy of comp and unref comp itself. All the contained
rectangles will also be copied, but the actual overlay pixel data buffers
contained in the rectangles are not copied.
Takes ownership of comp and returns a version of comp that is writable (i.e. can be modified). Will either return comp right away, or create a new writable copy of comp and unref comp itself. All the contained rectangles will also be copied, but the actual overlay pixel data buffers contained in the rectangles are not copied.