GNOME Mutter Adds Intermediate ShadowFB For Faster Software Rendering
The change by Red Hat's Olivier Fourdan introduces an intermediate shadow frame-buffer for applying of transformations to the in-memory frame-buffers before blitting to the screen. This intermediate shadowfb should "keep things fast(ish)" when lacking OpenGL hardware acceleration.
Fourdan describes the intermediate shadow frame-buffer support as now being fast enough for "achieve acceptable performance even with software rendering on discrete GPU."
More details on this Mutter change via the MR that was merged a short time ago.