Pekka Paalanen authored Nov 29, 2018 and Jonas Ådahl committed Jul 10, 2019

When the preferred path META_SHARED_FRAMEBUFFER_COPY_MODE_SECONDARY_GPU cannot
be used, as is the case for e.g. DisplayLink devices which do not actually have
a GPU, try to use the primary GPU for the copying before falling back to
read-pixels which is a CPU copy.

When the primary GPU copy works, it should be a significant performance win
over the CPU copy by avoiding stalling libmutter for the duration.

This also renames META_SHARED_FRAMEBUFFER_COPY_MODE_* because the new names are
more accurate. While the secondary GPU copy is always a GPU copy, the primary
copy might be either a CPU or a GPU copy.

!615