xlib.fallback occasionally incorrectly treats OVER as SOURCE
Submitted by Massimo
Assigned to Chris Wilson
Created attachment 106329 quick hack
the xlib.fallback composer calls a fill_reduces_to_source in src/cairo.image-compositor.c that simplifies an OVER operator fill to a SOURCE operator fill whenever the destination is clear.
This means that you have to mark the shm-image-surface as no longer clear after it is filled as the attached quick hack does.
over-above-source over-around-source over-between-source
Attachment 106329, "quick hack":