Daniel van Vugt 3a474556b8 cogl-texture-2d: Flush the journal before mipmapping
In the case of indirect rendering like the first frame to use mutter's
background wallpaper:

  Texture_A -> FBO_B (Texture_B) -> FBO_C (screen)

we would be trying to render the contents of both FBO_B and FBO_C in
the same flush, before the contents of Texture_A had made it to FBO_B.
So when FBO_C wants to use mipmaps of Texture_B they didn't exist yet
and appeared all black. And the blackness would remain for subsequent
frames as cogl has now decided the mipmaps of FBO_B are no longer
"dirty" and don't need refreshing:

  FBO_B (Texture_B) (mipmaps_dirty==FALSE but black) -> FBO_C (screen)

We must flush FBO_B before referencing Texture_B for use in rendering
FBO_C. This only happens when Texture_A changes (e.g. when the user
changes their background wallpaper) so there's no ongoing performance
penalty from this flush.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1347
2020-07-07 16:15:24 +08:00
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