[Mesa-dev] Anybody still need clear_depth_stencil() or clear_render_target()?

[Roland Scheidegger]

Am 02.12.2013 23:08, schrieb Andreas Hartmetz:
> Hello,
> 
> I've been lurking for a while, this seems to be my first post.
> 
> While trying to make some "easy" (ha) improvements in radeonsi I
> looked around in all the surrounding code to get a good picture of
> how things work. So I noticed something: All the Gallium drivers need
> to implement clear_depth_stencil() and clear_render_target() from
> pipe_context. Those implementations are generally using little to no
> acceleration, just making sure that there's any implementation at
> all. Still, it's quite a few lines over all the drivers. The two
> methods in question were introduced for Direct3D, which has no
> in-tree state tracker anymore, and for scissored clearing in OpenGL.
> But scissored clearing is already implemented as a fallback using
> quad drawing in the OpenGL state tracker (st_cb_clear.c, 
> clear_with_quad()) in pretty much the same way as the unoptimized
> paths in drivers.
> 
> So, the question arises: Does anybody still use those functions,
> maybe VMware in some out-of-tree code? If not I suggest removing them
> and I'd send patches to do that. Alternatively, they could be reduced
> to do just scissored clearing, and the OpenGL state tracker could
> call that in the hope that some GPU will have an optimized way to do
> it (how realistic is that? I have not looked at all the GPU
> drivers...).
>

Yes we have some internal use for them as they indeed map well to d3d
semantics.
That said the idea was they could also be used for the GL 3.0 single
color buffer attachment clears (the ClearBuffer commands). Looks though
like everyone (gallium and also i965 driver) just drops that argument on
the floor and clears all (color) attachments simultaneously always
anyway (?!?). Assuming I'm not missing anything and this is indeed a bug
then to fix that you'd either need to extend the gallium "ordinary"
clear semantics to be able to indicate the color attachment to clear, or
do a quad clear, or create a new fb for clearing, or just use these
commands... (Well ok only for render_target not depth_stencil since
there's no problem with multiple buffers there.)

Roland