By the looks of it, commit 95e9fa10ef was taping over an Intel DRI bug
that would make it return post-swizzling pixel data on glReadPixels().
There's been reports over time of that commit resulting in wrong colors
on other drivers, and lately Mesa >17.3 started showing the same symptoms
on Intel.
But texture swizzling works by changing parameters before fragment shaders
and reading pixels from an already drawn FBO/texture doesn't involve those.
This should thus use pixel_format_to_gl_with_target(), which will result in
correctly requesting the same pixel format than the underlying texture,
while still considering it BGRA for the upper layers in the swizzling case.
https://gitlab.gnome.org/GNOME/mutter/issues/72Closes: #72
44a7f74dcd