[Bug 29137] New: [r300g] troubles with wine and "r300: Max size of the constant buffer is 256*4 floats."

[Bug 29137] New: [r300g] troubles with wine and "r300: Max size of the constant buffer is 256*4 floats."

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https://bugs.freedesktop.org/show_bug.cgi?id=29137

           Summary: [r300g] troubles with wine and "r300: Max size of the
                    constant buffer is 256*4 floats."
           Product: Mesa
           Version: git
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/r300
        AssignedTo: dri-devel@lists.freedesktop.org
        ReportedBy: drakkk@centrum.cz


When running Sins of a Solar Empire under Wine all 3D objects are black, the
only thing which is rendered correctly are menus and control panels.
Main problem here is this massage: r300: Max size of the constant buffer is
256*4 floats.

Some time ago there was a bug 27996, however it was about crash and later I
forgot about this issue because I found a workaround (disabling use of GLSL in
Wine). 

>From bug 27996: "OK so the problem is the game creates a larger constant buffer
than hw can handle, but it seems to use only a small portion of the buffer.
I've changed the code so that it does not abort"
Since the game was working fine with this hardware in Windows (and my RV530 is
well above minimum requirements) I suspected this to be a Wine issue and I
asked at their forums, sadly with little response. Finally soreau at #radeon
said this in theory can be fixed in driver and advised to open a bug here.

This issue is not only affecting SoaSE, I also saw this message in wine d3d9
test run and when I was experimenting with other games like for example
Starcraft 2.

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[Bug 29137] [r300g] troubles with wine and "r300: Max size of the constant buffer is 256*4 floats."

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Sven Arvidsson <sa@whiz.se> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sa@whiz.se

--- Comment #1 from Sven Arvidsson <sa@whiz.se> 2010-07-18 05:58:01 PDT ---
Another good test case for this is 3DMark2001:
http://www.futuremark.com/download/3dmark2001/

I think most of the tests are affected, but its's most noticeable (missing
objects) in Dragothic (High Detail) and Nature. 

Both of these seems to be working okay if software rendering is forced.

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[Bug 29137] [r300g] troubles with wine and "r300: Max size of the constant buffer is 256*4 floats."

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--- Comment #2 from Henri Verbeet <hverbeet@gmail.com> 2010-07-19 05:01:53 PDT ---
(In reply to comment #0)
> When running Sins of a Solar Empire under Wine all 3D objects are black, the
> only thing which is rendered correctly are menus and control panels.
> Main problem here is this massage: r300: Max size of the constant buffer is
> 256*4 floats.
> 
For a part that's our (Wine's) fault for depending on the driver to properly
notice not all of those constants are actually used. On the other hand, trying
to avoid this in Wine itself would be somewhat complicated. We mainly depend on
the driver to notice that as long as you don't use non-const indices into an
uniform array, it's really just a set of independent constants, of which you
can eliminate the unused ones.

> Since the game was working fine with this hardware in Windows (and my RV530 is
> well above minimum requirements) I suspected this to be a Wine issue and I
> asked at their forums, sadly with little response. Finally soreau at #radeon
> said this in theory can be fixed in driver and advised to open a bug here.
> 
Yeah, not all Wine developers read the forums, and I'd only expect someone
fairly familiar with the wined3d code to be able to say something useful on the
subject.

As a quick workaround you could modify Wine to use a slightly smaller array in
shader_generate_glsl_declarations(), but we can't do that in general in Wine,
because some applications depend on being able to use the higher indices, even
if the total number of constants they use is nowhere near the limit.

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[Bug 29137] [r300g] troubles with wine and "r300: Max size of the constant buffer is 256*4 floats."

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--- Comment #3 from Pavel Ondračka <drakkk@centrum.cz> 2010-08-02 06:41:10 PDT ---
(In reply to comment #2)
> As a quick workaround you could modify Wine to use a slightly smaller array in
> shader_generate_glsl_declarations(), but we can't do that in general in Wine,
> because some applications depend on being able to use the higher indices, even
> if the total number of constants they use is nowhere near the limit.

I've had a look at shader_generate_glsl_declarations() function, however it is
quite complicated and I don't have any clue how to do this. I don't even know
if we are talking about some one liner patch or complete rewrite of this
function :-( Henri, if this is just a simple change would you be so kind to
write this patch for me, please? I don't know if this issue is going to be
fixed in the r300g driver any time soon.

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[Bug 29137] [r300g] troubles with wine and "r300: Max size of the constant buffer is 256*4 floats."

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--- Comment #4 from Henri Verbeet <hverbeet@gmail.com> 2010-08-02 06:52:06 PDT ---
Created an attachment (id=37525)
 View: https://bugs.freedesktop.org/attachment.cgi?id=37525
 Review: https://bugs.freedesktop.org/review?bug=29137&attachment=37525

wined3d hack

Something along the lines of the attached patch. You don't necessarily need the
changes in shader.c, but they avoid a similar problem.

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--- Comment #5 from Pavel Ondračka <drakkk@centrum.cz> 2010-08-02 07:31:59 PDT ---
(In reply to comment #4)
> Created an attachment (id=37525)
 View: https://bugs.freedesktop.org/attachment.cgi?id=37525
 Review: https://bugs.freedesktop.org/review?bug=29137&attachment=37525

> wined3d hack
> 
> Something along the lines of the attached patch. You don't necessarily need the
> changes in shader.c, but they avoid a similar problem.

Thank you with this hack Sins of a Solar Empire is working fine.

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[Bug 29137] [r300g] troubles with wine and "r300: Max size of the constant buffer is 256*4 floats."

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--- Comment #6 from Marek Olšák <maraeo@gmail.com> 2010-08-02 07:40:17 PDT ---
It won't certainly get fixed in r300g, we would have to reorder constants every
draw call, which would incur noticable perfomance drop (in Gallium, constant
buffers may be reused for several different shaders).

It might get fixed in the GLSL compiler, though, which resides in Mesa core.
I'd rather wait until Intel merge their new GLSL compiler before looking into
this issue.

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--- Comment #7 from Pavel Ondračka <drakkk@centrum.cz> 2010-08-02 07:57:10 PDT ---
One last question. Is it OK to report bugs spotted with this hack applied?

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[Bug 29137] [r300g] troubles with wine and "r300: Max size of the constant buffer is 256*4 floats."

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--- Comment #8 from Henri Verbeet <hverbeet@gmail.com> 2010-08-02 08:10:10 PDT ---
(In reply to comment #7)
> One last question. Is it OK to report bugs spotted with this hack applied?

The patch is fairly safe, but in general you shouldn't report (Wine) bugs with
modified source. The other consideration is that at least currently there's a
reasonably high chance that any (D3D/OpenGL) bugs you'll run into will be in
the driver instead of Wine. I'm certainly willing to help if there's anything I
can do to help track those down, but Wine bugzilla isn't the place for it.

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--- Comment #9 from Sven Arvidsson <sa@whiz.se> 2010-08-02 11:20:35 PDT ---
(In reply to comment #6)
> It won't certainly get fixed in r300g, we would have to reorder constants every
> draw call, which would incur noticable perfomance drop (in Gallium, constant
> buffers may be reused for several different shaders).
> 
> It might get fixed in the GLSL compiler, though, which resides in Mesa core.
> I'd rather wait until Intel merge their new GLSL compiler before looking into
> this issue.

Dunno if it's of any help (it being both different hardware and not Gallium)
but the i965 driver works quite well with Wine+GLSL.

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--- Comment #10 from Marek Olšák <maraeo@gmail.com> 2010-08-20 15:55:15 PDT ---
There is a new GLSL compiler in Mesa. Does it fix your issue?

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--- Comment #11 from Pavel Ondračka <drakkk@centrum.cz> 2010-08-20 16:07:31 PDT ---
(In reply to comment #10)
> There is a new GLSL compiler in Mesa. Does it fix your issue?

No it doesn't, there is no visible change.

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--- Comment #12 from Marek Olšák <maraeo@gmail.com> 2010-08-20 21:59:33 PDT ---
Henri,

I was thinking about this issue and realized that the way you allocate constant
space in wine is wrong. The problem is you create one large array "uniform vec4
VC[256]". If this array is addressed indirectly, that is using e.g.
VC[index+20] where "index" cannot be evaluated at compile time, we must assume
*any* element in the array may potentially be used and therefore we cannot
eliminate unused elements, because there appears to be none.

We can do the optimization if there is no indirect addressing, but we cannot do
this for all cases and say "it's fixed once and for all".

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--- Comment #13 from Henri Verbeet <hverbeet@gmail.com> 2010-08-21 06:02:33 PDT ---
(In reply to comment #12)
> Henri,
> 
> I was thinking about this issue and realized that the way you allocate constant
> space in wine is wrong. The problem is you create one large array "uniform vec4
> VC[256]". If this array is addressed indirectly, that is using e.g.
> VC[index+20] where "index" cannot be evaluated at compile time, we must assume
> *any* element in the array may potentially be used and therefore we cannot
> eliminate unused elements, because there appears to be none.
>
Yes, but that's because of the way d3d9 works. I.e., you just have one big
block of 256 float constants (in SM2 and SM3, SM1 only requires 96). Direct3D
10 and 11 constant buffers are much nicer in that regard. The problem is that
wined3d needs a couple of extra constants for its own fixups, and often the
driver needs a couple as well.

For shaders where no relative addressing is used, wined3d could declare
separate uniforms instead of one big array. We'll probably make that change in
the near/medium future, unless changes in Mesa make it a non-issue for us. I
nevertheless think it would be a valid enhancement to the Mesa GLSL compiler to
make that observation on its own.

> We can do the optimization if there is no indirect addressing, but we cannot do
> this for all cases and say "it's fixed once and for all".
Similarly, wined3d can't split up the d3d9 constant array when relative
addressing is used. This is not just a problem with Mesa for us, it affects
e.g. fglrx and pre-GF8 nvidia hardware as well. The reason this isn't much of
an issue on GF8+ nvidia hardware is that it simply reports 4096 uniforms as
being available. Extensions like NV_shader_buffer_load suggest GF8+ hardware
can simply access arbitrary buffer objects / video memory from a shader.

The workaround we use when relative addressing is used by a shader is to simply
subtract our internal constants, in addition to our (most likely flawed)
estimate of what the driver itself needs, from the number of constants
available to the application. This breaks down when applications allocate from
the end of the range of available constants. I.e., using c[255] while at the
same time using relative addressing for e.g. vertex blending.
http://bugs.winehq.org/show_bug.cgi?id=17818 is an example of a bug caused by
this.

In short, I don't expect Mesa to be able to do much, if anything, to help solve
this. There may be some things we can try on the Wine side though. For example,
on hardware the supports immediate constants like r600 we could take advantage
of that and just hardcode our fixups into the shaders, and have multiple
versions of the shader instead. These fixups are things like compensating for
differences in pixel center between d3d9 and GL, or texture origin when
rendering to an FBO, which at least some drivers will have to do themselves
anyway, but the other way around. If we get lucky they may even cancel out and
get optimized away. The y-flip when rendering to FBO is especially sad, because
it ends up being a multiplication by -1.0, which would often be free as a
negate. The other way out is that while we can't determine which uniforms are
read by the shader, we can determine which ones are set by the application.
Constants that are never set would be our best bet for stuffing our own fixups
in, although that strategy depends on the application really treating those as
undefined, rather than relying on them being set to e.g. 0.0.

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[Bug 29137] [r300g] troubles with wine and "r300: Max size of the constant buffer is 256*4 floats."

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Marek Olšák <maraeo@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rubenf3000@gmail.com

--- Comment #14 from Marek Olšák <maraeo@gmail.com> 2010-08-22 16:45:45 PDT ---
*** Bug 29741 has been marked as a duplicate of this bug. ***

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--- Comment #15 from Marek Olšák <maraeo@gmail.com> 2010-08-22 17:49:34 PDT ---
I was discussing this with other devs and the conclusion is that this will not
be optimized in Mesa's GLSL compiler because if you use at least one element of
an array, the entire array becomes an "active" uniform and glUniform must then
succeed for all (even unused) elements. Therefore all elements must be
allocated in the constant register file after the compilation.

I am working on elimination of unused constants in the r300 compiler. I am
already finished with vertex shaders, but still, if a shader uses relative
addressing, there is nothing I can do. There is no way to make the shader
compile successfully in this case.

As far as I remember, a D3D9 shader should declare just the constants it uses
and/or ranges of used constants, not the entire constant space available. I
don't remember the exact syntax of D3D9 assembly, but I doubt the HLSL compiler
declares a sequence of definitions similar to this in an asm shader:

def c0
...
def c255

Instead, I think it just contains the definitions of constants the shader
actually needs, and Wine should search for a max index and use that (+1)
instead of 256. If one shader declares the 255th constant, let's make only this
shader declare the array of 256 elements, but there is no need to declare it so
large for every other shader out there.

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--- Comment #16 from Rubén Fernández <rubenf3000@gmail.com> 2010-08-23 04:43:33 PDT ---
If it is of any help, aplyint that wined3d hack makes all the wine applications
I have tested render correctly except for two games:

One of them still complains about "r300: Max size of the constant buffer is
256*4 floats."

The other fails when a shader attempts to access the elements #30 and #31 in a
29-element array; presumably, without the patch, said array would be 32
elements long.

As far as I can see, this bug is the only thing preventing wine+glsl to work
perfectly with mesa+r300g.

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--- Comment #17 from Marek Olšák <maraeo@gmail.com> 2010-08-24 18:07:05 PDT ---
So I've implemented elimination of unused constants (and remapping their
indices to fit in the constant file in hw, and other compiler improvements) in
r300g. Wine support should be much better and indeed more Wine/D3D9 tests pass
now.

If some shaders still fail due to these reasons:
- relative addressing (indexing) of constants while using a too large uniform
array
- exceeding the maximum number of constants by other means

There is nothing I can do about it.

Please test.

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Pavel Ondračka <drakkk@centrum.cz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #18 from Pavel Ondračka <drakkk@centrum.cz> 2010-08-25 00:55:05 PDT ---
My both test cases (SoaSE and SC2) don't have this problem any more and no
regressions encountered so far. Thank you Marek. Closing.

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--- Comment #19 from Rubén Fernández <rubenf3000@gmail.com> 2010-08-25 02:55:19 PDT ---
Seconded. I have tested it with all the wine stuff I have. wine+GLSL behaved
exactly like it does without GLSL in almost all cases, and even in those it
didn't, it didn't complain about constant buffers or indexes. I consider this
bug resolved, too. Excellent work, Marek!

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