glamor_init: clamp GLSL to 120 if platform doesn't have instanced arrays

[Lukas F. Hartmann]

Adam Jackson <ajax at nwnk.net> writes:

> I'm somewhat surprised Mesa doesn't expose any of ANGLE/EXT/NV in GLES2
> contexts. If it did so - and if etnaviv actually implemented instanced
> rendering, which it definitely has code to sometimes do - then I
> suspect you wouldn't need this patch.

Also there is currently no codepath that creates a GLES context in
Xwayland, there is only EGL_OPENGL_API:
https://cgit.freedesktop.org/xorg/xserver/tree/hw/xwayland/xwayland-glamor-gbm.c#n789

On the other hand, "standalone" glamor has a corresponding codepath for it:
https://github.com/mirror/xserver/blob/9d628ee5facf6318368d5b8ca181e083adcffe8c/glamor/glamor_egl.c#L957

But this is only triggered if there is no Desktop GL available at all on
the platform. I tried earlier today to switch the init in
xwayland-glamor-gbm.c to use EGL_OPENGL_ES_API but then I had severe
rendering errors on etnaviv with most text and icons missing.

BTW in parallel this patch was posted to mesa today to downgrade GLSL to 120
as well:
https://lists.freedesktop.org/archives/mesa-dev/2018-May/195060.html

Thanks for merging!

Cheers
Lukas