[Mesa-dev] [PATCH] st/mesa: add a fallback for clear_with_quad when no vs_layer

[Jose Fonseca]

Hi Marek,

> First of all, sorry for breaking Draw yesterday.

No problem. draw_llvm.c was really obfuscating the fact that it relied on the layout of the pipe_viewport_state.

> There's also the OpenGL extension AMD_vertex_shader_layer which is
> supported by all GS-capable Mesa drivers except for nouveau and
> llvmpipe I think.

I see. It sounds we should try to support these things from vs then.

> tgsi_parse is something else. Did you mean tgsi_text_translate?

Yes, I meant tgsi_text_translate.

> I
> don't like using ureg for helper shaders unless I have to. Shaders
> written with ureg are harder to read and the code is longer. I've been
> thinking of rewriting all simple shaders to text.

I don't think that's a good idea.

Besides all the reasons I said before, string constants are not convenient to parameterize.  One needs to have multiple versions of the text file, or use snprintf. either way quite ugly.

Regarding readability, if one has a comment before the code is just as readable. This is not what's done in u_simple_shaders.c, but we use this approach elsewhere and it works quite nicely:

   [...]

   /* DP3 TEMP.w, SRC, SRC */
   ureg_DP3(tbi->prog, temp_dst_w, src, src);

   /* RSQ TEMP.w, TEMP.w */
   ureg_RSQ(tbi->prog, temp_dst_w, temp_src_w);

   [...]


If people feel strongly about writing helper TGSI shaders in plain text, then we should create a simple off-line compilation tool that compiles the TGSI and creates *.h files (similar like DirectX HLSL tools).


Jose

PS: Apologies for quoting only parts of the email. I'm sort of limited to using Outlook Web Access for email when working from home, and need to manually quote...
  
________________________________________
From: Marek Olšák <maraeo at gmail.com>
Sent: 16 November 2014 15:51
To: Jose Fonseca
Cc: Ilia Mirkin; mesa-dev at lists.freedesktop.org; 10.3 10.4
Subject: Re: [Mesa-dev] [PATCH] st/mesa: add a fallback for clear_with_quad when no vs_layer

Hi Jose,

First of all, sorry for breaking Draw yesterday.

On Sun, Nov 16, 2014 at 2:57 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
>> Fun fact -- llvmpipe also needs this.
>
> I think this is because this functionality was developed with D3D10 in mind, and
>
> https://urldefense.proofpoint.com/v2/url?u=http-3A__msdn.microsoft.com_en-2Dgb_library_windows_desktop_bb509647.aspx&d=AAIBaQ&c=Sqcl0Ez6M0X8aeM67LKIiDJAXVeAw-YihVMNtXt-uEs&r=zfmBZnnVGHeYde45pMKNnVyzeaZbdIqVLprmZCM2zzE&m=W_WiVknXaiEWMUhwH9NoKnxZ7SZQGp1B1VyLSBhv0rU&s=hwsRL-R8OHz5lpkwIvnmSRlHe-ijQAReKLFMkeVDWHM&e=
>
> states that SV_RenderTargetArrayIndex "an be written from the geometry shader and read by the pixel shader."

There's also the OpenGL extension AMD_vertex_shader_layer which is
supported by all GS-capable Mesa drivers except for nouveau and
llvmpipe I think.

>
>
> BTW, coding these helper shaders as text is not a great idea IMO:
>
> - The tgsi_parse thing was written for debugging purposes mainly.
>
> - Whenever there are TGSI interface changes, any breakage with ureg will cause compile errors, where as it will only be detected at runtime with TGSI
>
> - ureg module makes it really easy to write shaders.  It's not really much more work.

tgsi_parse is something else. Did you mean tgsi_text_translate? I
don't like using ureg for helper shaders unless I have to. Shaders
written with ureg are harder to read and the code is longer. I've been
thinking of rewriting all simple shaders to text.

Marek