Emma Anholt authored Feb 01, 2016 and Adam Jackson committed Mar 10, 2016

For pictures without alpha, and for most other formats for GLES2, we
would make a temporary FBO, make another temporary texture, upload our
GLAMOR_MEMORY pixmap to the texture, then run the "finish access" shader
across it to swizzle its values around into the temporary FBO (which we
would use for a single Render operation and then throw away).

We can simplify everything by using GL_ARB_texture_swizzle (or its
GLES3 counterpart).  It's just not worth the complexity to try to
improve the performance of this already low-performance path (SHM
pixmaps + Render) on GLES2.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Eric Anholt <eric@anholt.net>