[Mesa-dev] st/pbo: fix pbo uploads without PIPE_CAP_TGSI_VS_LAYER_VIEWPORT

[Mike Blumenkrantz]

Hi Ilia,

I'm not entirely sure what you're asking here.

This patch doesn't change anything related to gl_Layer reads, it just
forces the geometry shader codepath unconditionally when VS_LAYER_VIEWPORT
isn't enabled in order to successfully write the gl_Layer output. If
anything, this should be beneficial to those nvidia chipsets based on your
description since previously the fragment shader would've had nothing to
read.


Mike

On Mon, Dec 14, 2020 at 10:48 AM Ilia Mirkin <imirkin at alum.mit.edu> wrote:

> Hey Mike,
>
> This is in reference to your change
>
> https://cgit.freedesktop.org/mesa/mesa/commit/?id=614c77772ac2f48955537efcfefaf0609d6c03e5
> .
>
> A fragment shader should still be able to read gl_Layer even without
> PIPE_CAP_TGSI_VS_LAYER_VIEWPORT. A frag shader can read gl_Layer any
> time ARB_fragment_layer_viewport is supported -- I forget the precise
> conditions for it, but basically any DX10 hardware supports that.
>
> However the VS_LAYER_VIEWPORT feature isn't supported on any NVIDIA
> hardware until fairly late models (GM20x+). So this will regress the
> majority case (single-layer) on all NVIDIA hw.
>
> Can you instead adjust the conditions to allow this for the drivers
> that implement layer/viewport sysvals in frag shaders? Or just
> implement ARB_fragment_layer_viewport in zink?
>
> Thanks,
>
>   -ilia
>
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