Make software compositing fallback work

[Chris Coulson]

Currently we fall back correctly to software compositing in the case where GPU compositing or GPU access is disabled in the GPU blacklist. However, we don't fall back if we can't do GPU compositing for some other reason (eg, failure to create a context). This leads to crashes like bug 1520537

[Daniel van Vugt (vanvugt)]

Is that a good idea? If it fell back seamlessly then you would not get major bug reports (LP: #1520537) and a fix so quickly. Just a long slow process of people wondering "why is this slower than it used to be?".

We experience the same with Unity7 right now. The fallback to software rendering is so transparent (and performs so well) that many people can't immediately notice when it has happened. So they don't report a bug and just endure lower performance.

[Olivier Tilloy (osomon)]

Perhaps add a big fat warning (IN ALL CAPS) that will end up in the app’s log when falling back to software compositing, so that at least people looking into performance issues will get a hint of what’s going on?