[Mesa-dev] [Mesa3d-dev] [PATCH 0/6] [RFC] Formalization of the Gallium shader semantics linkage model

Fri Dec 17 08:54:35 PST 2010

On Fri, Dec 17, 2010 at 4:32 PM, Brian Paul <brianp at vmware.com> wrote:

> Christoph,
>
> I don't see a patch for the st/mesa program translation code to check
> that we don't exceed the limit.  Were you doing to take care of that too?
>
> I guess we're assuming that the max number of generic inputs == max
> number of generic outputs.  I think that's OK until a counter case
> appears.
>

The way I understand it is that the max number of generic outputs is equal
to the max number of generic inputs in the next shader stage (the same logic
applies to some other shader caps too). I guess we need to use get_param to
determine which shader stages are supported by the driver to know which one
is next. The name *PIPE_SHADER_CAP_MAX_GENERIC_INPUT_INDEX* would be less
ambiguous (still not perfect though).

However I don't believe in usefulness of this new cap, at least not without
some serious state tracker work. I don't consider failing to translate a
shader if some CAP is too low particularly useful.

(posting to mesa-dev as well)

Marek

> -Brian
>
>
> On 12/17/2010 05:28 AM, Keith Whitwell wrote:
> > Christoph,
> >
> > This looks good.  Thanks for bringing this back to life.
> >
> > Keith
> >
> > On Thu, 2010-12-16 at 07:47 -0800, Christoph Bumiller wrote:
> >> On 12/14/2010 12:36 PM, Keith Whitwell wrote:
> >>> On Mon, 2010-12-13 at 12:01 -0800, Christoph Bumiller wrote:
> >>>> I want to warm this up again adding nvc0 and
> >>>> GL_ARB_separate_shader_objects to the picture.
> >>>>
> >>>> The latter extends GL_EXT_separate_shader_objects to support user
> >>>> defined varyings and guarantees well defined behaviour only if
> >>>> - varyings are declared inside the gl_PerVertex/gl_PerFragment block
> the
> >>>> blocks match exactly in name, type, qualification, and (most
> >>>> significantly) declaration order.
> >>>> - varyings are assigned matching location qualifiers:
> >>>> like: layout(location = 3) in vec4 normal
> >>>> "The number of input locations available to a shader is limited."
> >>>>
> >>>> So, I propose to (loosely) identify GENERIC semantic indices with
> these
> >>>> location qualifiers and let the pipe driver set a limit on the allowed
> >>>> maximum (e.g PIPE_SHADER_CAP_MAX_INPUTS, and not demand to at least
> >>>> support 219 of them - nvc0 offsers 0x200 bytes for generic
> inputs/outputs).
> >>>
> >>> This sounds fine actually.  We kicked this around before&  I was
> >>> basically ok with the last iteration of the proposal, but this seems ok
> >>> too.
> >>>
> >>> As far as I can tell from a gallium perspective you're really just
> >>> proposing a new pipe cap _MAX_INPUTS (actually _MAX_GENERIC_INDEX would
> >>> be clearer), which the state tracker thereafter has to respect?
> >>>
> >>> That would be fine with me.
> >> First attempt at a patch introducing such a cap attached.
> >>
> >>>
> >>>> My motivation is mostly that the hardware routing table for shader
> >>>> varyings that was present on nv50 has been removed with nvc0 (Fermi).
> >>>> And I'm glad, because filling 4 routing tables (since we have 5 shader
> >>>> types now) is somewhat annoying. And so applying relocations to
> shaders
> >>>> - it can be done, it's probably not too time consuming, but it's just
> >>>> plain *unnecessary* (and thus stupid) for OpenGL.
> >>>>
> >>>> Now about d3d9 ...
> >>>> 1. don't care, I don't see a d3d9 state tracker
> >>>> 2. http://msdn.microsoft.com/en-us/library/bb509647%28v=VS.85%29.aspx
> >>>> says "n is an optional integer between 0 and the number of resources
> >>>> supported" - what "supported" means here isn't clear to me, but, I
> >>>> didn't find any example where someone used something OpenGL doesn't
> have
> >>>> (like COLOR2).
> >>>> 3.
> >>>>
> http://msdn.microsoft.com/en-us/library/bb944006%28v=vs.85%29.aspx#Varying_Shader_Inputs_and_Semantics
> >>>> says "Input semantics are similar to the values in the D3DDECLUSAGE."
> >>>> and
> >>>> DECLUSAGE sounds like you're limited to sane values.
> >>>
> >>> I think you're on the right track with (1)...  It's fairly pointless
> >>> trying to discuss code here which isn't public&  I don't think people
> >>> need to be worrying about what may or may not be important for code
> they
> >>> can't see.
> >>>
> >>> I know this idea previously got tied up with speculation about what a
> >>> DX9 state tracker might or might not require, but in retrospect I wish
> >>> I'd been able to steer conversation away from that.
> >>>
> >>> The work on closed components may drive a lot of the feature
> development
> >>> and new interfaces, but there's usually enough flexibility that this
> >>> sort of cleanup isn't a big deal.
> >>>
> >>>
> >>> Keith
> >>>
> >>>> Not sure if anyone wants to think about this issue at this time (since
> >>>> implementation of ARB_separate_shader_objects is probably far in the
> GL4
> >>>> future), but I'd be happy about any comments.
> >>>>
> >>>> Regards,
> >>>> Christoph
> >>>>
> >>>> On 04/13/2010 12:55 PM, Luca Barbieri wrote:
> >>>>> This patch series is intended to resolve the issue of semantic-based
> shader linkage in Gallium.
> >>>>> It can also be found in the RFC-gallium-semantics branch.
> >>>>>
> >>>>> It does not change the current Gallium design, but rather formalizes
> some limitations to it, and provides infrastructure to implement this model
> more easily in drivers, along with a full nv30/nv40 implementation.
> >>>>>
> >>>>> These limitations are added to allow an efficient implementation for
> both hardware lacking special support and hardware having support but also
> special constraints.
> >>>>>
> >>>>> Note that this does NOT resolve all issues, and there are quite a bit
> left to future refinement.
> >>>>>
> >>>>> In particular, the following issues are still open:
> >>>>> 1. COLOR clamping (and floating point framebuffers)
> >>>>> 2. A linkage table CSO allowing to specify non-identity linkage
> >>>>> 3. BCOLOR/FACE-related issues
> >>>>> 4. Adding a cap to inform the state tracker that more than 219
> generic indices are provided
> >>>>>
> >>>>> This topic was already very extensively discussed.
> >>>>> See
> http://www.mail-archive.com/mesa3d-dev@lists.sourceforge.net/msg10865.htmlfor some early inconclusive discussion around an early implementation that
> modified the GLSL linker (which is NOT being proposed here)
> >>>>> See
> http://www.mail-archive.com/mesa3d-dev@lists.sourceforge.net/msg12016.htmlfor some more discussion that seemed to mostly reach a consensus over the
> approach proposed here.
> >>>>> See in particular
> http://www.mail-archive.com/mesa3d-dev@lists.sourceforge.net/msg12041.html.
> >>>>>
> >>>>> That said, I'm going to try to repeat all information here, partially
> by copy&pasting from earlier messages.
> >>>>> This message should probably be adapted into gallium/docs if/when
> this is accepted.
> >>>>>
> >>>>> Here is the short summary; the long rationale follows after it.
> >>>>>
> >>>>> The proposal here is to add the following limitations to Gallium, for
> the intermediate semantics:
> >>>>> 1. TGSI_SEMANTIC_NORMAL is removed, using a commit by Michal Krol
> that was never merged
> >>>>> 2. Every semantic except GENERIC, COLOR and BCOLOR can only be used
> with semantic index 0
> >>>>> 3. COLOR and BCOLOR can only be used with semantic index 0-1 (note
> that this doesn't apply to fragment outputs)
> >>>>> 4. GENERIC can be used with semantic indices 0-218 on any driver, if
> BCOLOR is not used
> >>>>> 5. GENERIC can be used with semantic indices 0-216 on any driver, if
> BCOLOR IS used
> >>>>> 6. GENERIC can be used with semantic indices 0-255 on almost all
> drivers (those that don't need the 0-218 limitation)
> >>>>> 7. Some drivers may also choose to support GENERIC with arbitrary
> indices, but that should generally not happen
> >>>>>
> >>>>> The reason of this, in short, is that this maps directly to DirectX 9
> SM3, which is the most problematic interface of all.
> >>>>>
> >>>>> The peculiar problem we have here is that we have two competing
> constraints that force us into choosing the exact SM3 value:
> >>>>> 1. The VMware SVGA driver must deal with an SM3 host interface and
> would ideally want to directly feed the Gallium semantics to the host
> >>>>> 2. An hypotetical DirectX 9 state tracker needs to support SM3 and
> would ideally want to directly feed the SM3 semantics to Gallium
> >>>>>
> >>>>> Note that this is not a reference to the VMware DirectX 9 state
> tracker, since its authors haven't provided details about its handling of
> shader semantics.
> >>>>>
> >>>>> SM3 ends up supporting 219 generic indices: 16 indices in 14 classes,
> minus POSITION0, PSIZE0, COLOR0, COLOR1 and FOG0 which are the only ones
> that wouldn't be mapped to GENERIC.
> >>>>> However, Gallium drivers that don't benefit from having specific
> contraints (like svga and r600) are supposed to support 256 indices, and my
> nv30/nv40 work does that.
> >>>>>
> >>>>> The expected implementation, if no hardware support exists, is to
> build a list of relocations to apply to either the fragment or the vertex
> shader, and patch one of them at validation time to match the other.
> >>>>> Data structures are provided in gallium/auxiliary to ease this, and
> try to minimize the number of times where this needs to be performed.
> >>>>>
> >>>>> Let's now proceed to the discussion and detailed rationale, mostly
> constructed by copy&pasting older messages.
> >>>>> ...
> >
> >
> >
> >
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