[Cogl] Cogl rendering to framebuffer on Raspberry Pi

[Stephen J]

Hi everyone,

I'm currently trying to get some Clutter demo code running on my Raspberry
Pi, using EGL. My goal is to be able to run the various demos without
modifying the demo code/binary, and use Cogl's egl backend to do the
rendering (with modifications to perform the RasPi specific initialization
routines). The demos do run in X when clutter/cogl is configured to do so,
although very slowly.

>From what I can tell, it looks like I should be setting COGL_DRIVER=gles2,
and then COGL_RENDERER=egl_null, modifying the egl_null driver to fit this
use case. It's not entirely clear whether the egl_null driver is just a
stub or whether it's just a generic egl->framebuffer driver, as opposed to
an android specific one such as egl_android. The Raspberry Pi's Broadcom
VC4 does not support KMS.

The link below is a raspberry pi demo, which draws directly to the
framebuffer using raw egl calls. The initialization code is very similar to
the egl_null initialization process.
https://github.com/raspberrypi/firmware/tree/master/opt/vc/src/hello_pi/hello_triangle2

So far, I've had no success.

The questions: Is egl_null the correct renderer to be using/modifying for
this use case? Do you know of anyone who has already succeeded with this?
Are the COGL_* environment variables documented anywhere?

Thanks!

--
Stephen Just
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