[Mesa-dev] [PATCH 0/5] Head-up display for Gallium DRI2 drivers

[Marek Olšák]

That's a very good question. There are a couple of reasons for this.

1) Writing any kind of meta operation and custom rendering code on top
of GL is a horrible idea and very prone to errors. If you don't
restore all states after you're done, you may break the application.
If the application sets a state you didn't take into account, it may
break the HUD rendering. And there is a lot of functionality in GL
that must be taken into account, while it's pretty simple with
Gallium, which has tools for saving and restoring states.

2) I would have to add code paths for GL2, GL3 core, GLES1, and GLES2.
I don't really want to worry about all those APIs or any future API.
It might also be interesting to use the HUD with non-OpenGL state
trackers, like st/xorg and st/xa.

3) Gallium has lower overhead than GL and the HUD should have as
little impact on framerate as possible.

I'm pretty sure everybody will benefit from this except Intel. I
wholeheartedly wish the situation were different, but there is nothing
I can do about that.

Marek

On Mon, Mar 25, 2013 at 5:47 PM, Alexander Monakov <amonakov at gmail.com> wrote:
> I feel rather awkward asking, but: why implement this inside of
> Gallium, instead of as a standalone {egl,glX}SwapBuffers interceptor
> obtaining counter values via GL extensions, such as
> ARB_occlusion_query or AMD_performance_monitor?  That way Intel (and
> Nouveau?) people could also benefit from it.
>
> Best regards,
> Alexander