in the original commit, that removed the conditional clearing, an
incorrect assumption was made that clearing "should be practically free"
and can be done always. though, at least on macOS + intel this can have
a performance impact of up to 50% increased usage. it might have an
impact on other platforms and setups as well, but this is unconfirmed.
the reason for removing the conditional clearing was to partially work
around a driver bug on very specific setups, X11 with amdgpu and OpenGL,
to clear garbled frames on start. though it still has issues with
garbled frames in other situation like fullscreening. there is also an
open bug report on the mesa bug tracker about this. setting the
radeonsi_zerovram flag works around all of those issues.
since the flag works around all these issues and the original fix
doesn't work completely we revert it and keep our optimisation.
Fixes#8273
b8156a9a86