Hm, I thought reading gl_Layer in a fragment shader is well-defined (to be 0) when there's no GS. Reading back over ARB_fragment_layer_viewport, it doesn't seem to address this point at all. It just says that if GS doesn't write gl_Layer, then it will be read as 0 by the fragment shader. I'd be curious if there are any interpretations that allow this case to be undefined.
It's definitely the case on NVIDIA hw that you'll get a 0 (since it reflects the layer being rendered). The pbo logic has worked well on NVIDIA hw for many years, so this is just a regression there. Cheers, -ilia On Mon, Dec 14, 2020 at 10:55 AM Mike Blumenkrantz <michael.blumenkra...@gmail.com> wrote: > > 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 <imir...@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 _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
