Dear Andreas, since writing this last year I've switched to the XFCE desktop with Arch OpenRC and Void Linux, so I can't reproduce the bug in order to fix it now. I also think the Gnome crew may have alternative plans to using Open GL derived libraries in future for drawing if I understand this advice correctly:
GTK+ 3 Reference Manual version 3.20.9 Common Questions — Find answers to common questions in the GTK+ manual 6.2. Can I improve the performance of my application by using the Glitz or GL backend of cairo ? No. The GDK X11 backend uses the cairo X backend (and the other GDK backends use their respective native cairo backends). The GTK+ developers believe that the best way to improving the GDK drawing performance is to optimize the cairo X backend and the relevant code paths in the X server that is uses (mostly the Render extension). >From what I've read, although I haven't tested the results as I'm no longer >using Debian, it was decided to fix this problem at a higher level in the >'mesa' packages and updated versions of these are currently available as >backports for Debian Jessie. These patches were mainly intended as a fix for a bug in a particular version of various Gnome desktop elements, for Debian users to apply themselves or as a Debian patch if this solution had been desired. It was just a case of updating what was there according to the guidelines in the relevant version of the COGL manual so there was a fallback path in the event of using a graphics card without all the features required by the original code. Thanks for your reply, if any of these patches were useful to anyone then they would of course be welcome to use them. If you wanted, this bug could be closed to tidy things up as it no longer bugs me :).
