im_invalidate - flush caches related to an image
void im_invalidate( IMAGE *im )
im_invalidate(3) marks all caches related to the image as invalid and
requring recalculation. It needs to be called if an image changes
after being made: for example, after a paint action, or perhaps after a
new frame has arrived from a video source.
Any invalidate callbacks registered on any of the affected images are
im_prepare(3), im_region_buffer(3), im_add_invalidate_callback(3).
5 December 2006