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Re: tracking OpenGL support for specific boards




> > Many of those chipsets you list, as I understand, have a mesa driver
> > for them that support opengl and gles.
> > Such as freedreno which supports A4XX series. https://mesamatrix.net/
> >
> > Keep in mind, only the proprietary drivers seem to not support opengl
> > while the hardware is perfectly capable of doing so.
>
> Not necessarily.
> If the manufacturer specifies OpenGL ES support, then - on the hardware
> level - it is a GLES renderer and may or may not support the entire
> OpenGL specification natively. It usually requires considerable work to
> make GLES hardware support OpenGL.
> Eric Anhold can tell you all about the hard work he has put into
> bastardising his VC4 mesa driver to make up for the lack of hardware
> support:
>

When Eric jumped from Intel to Broadcom, I was there at the beginning
of his VC4 work doing testing and getting OpenMW running on the RPi.
One of our conversations revolved around why only GLES support and not
full GL support in the binary blob and his answer was that VC4 can do
both but only to a point, it depends entirely on what the hardware is
capable of. VC4 is fully capable of OpenGL 2.1 but with a few more
extensions that were GLES 2.0 specific. No bastardisation. His biggest
hurdle (still?) is dealing with the fact that the VC4 has no memory
space protection because there is no MMU. He has to use a CMA which is
_very_ slow and has had to put in a ton of work to get that working.
[1] That has nothing to do with what the GPU was capable of in terms
of GL/GLES. You can't have GLES 2.0 without first having GLES 1.1
which is backwards compatible with OpenGL 1.5 in hardware.

That is why I stated that it is the driver developer that makes the
decision as to what is exposed which is a cost/price decision of the
company pushing the hardware. If they only have to target GLES then
why expose GL? Less time to market and less money spent in
development?

Take for example the S3TC opengl extension: EXT_texture_compression_s3tc
This is not supported in hardware which is the reason, even after the
patent was expired, that Eric (or anyone) could not implement it.
Broadcom simply didn't bother (cost cutting?). So if you ever have
texture that loads in with a S3TC, all you'll see is pink (or whatever
is used as alpha).

There is no, if extension doesn't exist, we'll just emulate it in
software in VC4.

I would be seriously flabbergasted if there was a chipset out there
that supported GLES2, that on hardware, wasn't capable of at least
OpenGL 1.5. I'm talking about on hardware, not a proprietary binary
blog that only exposes GLES.

> https://github.com/anholt/mesa/wiki/VC4-OpenGL-support
>

I know, I've posted this several time in previous Qt related threads. :)

Cheers,
Bret

[1] https://dri.freedesktop.org/docs/drm/gpu/vc4.html