[Merge] ~smspillaz/compiz:buffer-age-egl into compiz:master

[Sam Spilsbury]

Sam Spilsbury has proposed merging ~smspillaz/compiz:buffer-age-egl into compiz:master.

Commit message:
Enable EGL_EXT_buffer_age on USE_GLES where it is advertised.

buffer_age is long-since supported on GLES platforms, we can also use it there too with minimal changes. Tested on vc4 (Rasberry Pi 4).

A nice side-effect of this is that we don't have to draw the whole scene into an fbo and then redraw it later, just so that we can get double-buffering. Which should be nice on fillrate-bound GPUs.

Requested reviews:
  Compiz Maintainers (compiz-team)

For more details, see:
https://code.launchpad.net/~smspillaz/compiz/+git/compiz/+merge/412181

Enable EGL_EXT_buffer_age on USE_GLES

buffer_age is long-since supported on GLES platforms, we can also use it there too with minimal changes. Tested on vc4 (Rasberry Pi 4).

A nice side-effect of this is that we don't have to draw the whole scene into an fbo and then redraw it later, just so that we can get double-buffering. Which should be nice on fillrate-bound GPUs.

Probably this should be tested on a few other platforms before merging, I am unsure if there are drivers for which this is broken. At least cogl appears to support it, so maybe its not too bad on other drivers: https://gitlab.gnome.org/GNOME/mutter/-/blob/main/cogl/cogl/winsys/cogl-onscreen-egl.c#L165 .
-- 
Your team Compiz Maintainers is requested to review the proposed merge of ~smspillaz/compiz:buffer-age-egl into compiz:master.
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