Retrieves the region that is currently being repainted.
After a call to [[email protected]_frame] this function will return a union of the region passed to that function and the area of the surface that the this determined needs to be repainted.
If this is not in between calls to [[email protected]_frame] and [ [email protected]_frame], null will be returned.
| this |
a `GdkDrawContext` |
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a Cairo region |