On 09/13/2013 01:45 PM, Paul Berry wrote:
> On 11 September 2013 16:28, Ian Romanick <i...@freedesktop.org
> <mailto:i...@freedesktop.org>> wrote:
>
> On 09/11/2013 04:05 PM, Paul Berry wrote:
> > On 10 September 2013 12:10, Ian Romanick <i...@freedesktop.org
> <mailto:i...@freedesktop.org>
> > <mailto:i...@freedesktop.org <mailto:i...@freedesktop.org>>> wrote:
> >
> > From: Ian Romanick <ian.d.roman...@intel.com
> <mailto:ian.d.roman...@intel.com>
> > <mailto:ian.d.roman...@intel.com
> <mailto:ian.d.roman...@intel.com>>>
> >
> > Signed-off-by: Ian Romanick <ian.d.roman...@intel.com
> <mailto:ian.d.roman...@intel.com>
> > <mailto:ian.d.roman...@intel.com
> <mailto:ian.d.roman...@intel.com>>>
> > ---
> > src/mesa/main/get.c | 4 ----
> > src/mesa/main/get_hash_params.py | 2 +-
> > 2 files changed, 1 insertion(+), 5 deletions(-)
> >
> > diff --git a/src/mesa/main/get.c b/src/mesa/main/get.c
> > index 34eb6be..ae45bf8 100644
> > --- a/src/mesa/main/get.c
> > +++ b/src/mesa/main/get.c
> > @@ -718,10 +718,6 @@ find_custom_value(struct gl_context *ctx,
> const
> > struct value_desc *d, union valu
> > ASSERT(v->value_int_n.n <=
> ARRAY_SIZE(v->value_int_n.ints));
> > break;
> >
> > - case GL_MAX_VARYING_FLOATS_ARB:
> > - v->value_int = ctx->Const.MaxVarying * 4;
> > - break;
> > -
> > /* Various object names */
> >
> > case GL_TEXTURE_BINDING_1D:
> > diff --git a/src/mesa/main/get_hash_params.py
> > b/src/mesa/main/get_hash_params.py
> > index c0dbf45..3d47443 100644
> > --- a/src/mesa/main/get_hash_params.py
> > +++ b/src/mesa/main/get_hash_params.py
> > @@ -365,7 +365,7 @@ descriptor=[
> >
> > # GL_ARB_vertex_shader
> > [ "MAX_VERTEX_UNIFORM_COMPONENTS_ARB",
> > "CONTEXT_INT(Const.VertexProgram.MaxUniformComponents),
> > extra_ARB_vertex_shader" ],
> > - [ "MAX_VARYING_FLOATS_ARB", "LOC_CUSTOM, TYPE_INT, 0,
> > extra_ARB_vertex_shader" ],
> > + [ "MAX_VARYING_FLOATS_ARB",
> > "CONTEXT_INT(Const.VertexProgram.MaxOutputComponents),
> > extra_ARB_vertex_shader" ],
> >
> > # GL_EXT_framebuffer_blit
> > # NOTE: GL_DRAW_FRAMEBUFFER_BINDING_EXT ==
> GL_FRAMEBUFFER_BINDING_EXT
> > --
> > 1.8.1.4
> >
> > _______________________________________________
> > mesa-dev mailing list
> > mesa-dev@lists.freedesktop.org
> <mailto:mesa-dev@lists.freedesktop.org>
> <mailto:mesa-dev@lists.freedesktop.org
> <mailto:mesa-dev@lists.freedesktop.org>>
> > http://lists.freedesktop.org/mailman/listinfo/mesa-dev
> >
> > Doesn't MAX_VARYING_FLOATS need to be
> MIN2(MAX_VERTEX_OUTPUT_COMPONENTS,
> > MAX_FRAGMENT_INPUT_COMPONENTS)? I can imagine an implementation where
> > MAX_FRAGMENT_INPUT_COMPONENTS is the smaller constraint (in fact,
> ES3's
> > minimum maximums constitute just such a case).
>
> It's all so much more horrible than you think. :)
>
> OpenGL 3.2 sets:
>
> MAX_VARYING_COMPONENTS: 60
> MAX_VERTEX_OUTPUT_COMPONENTS: 64
> MAX_FRAGMENT_INPUT_COMPONENTS: 128
>
> OpenGL ES 3.0 sets:
>
> MAX_VARYING_COMPONENTS: 60
> MAX_VARYING_VECTORS: 15
> MAX_VERTEX_OUTPUT_VECTORS: 16
> MAX_VERTEX_OUTPUT_COMPONENTS: 64
> MAX_FRAGMENT_INPUT_VECTORS: 15
> MAX_FRAGMENT_INPUT_COMPONENTS: 60
>
>
> Oddly, I don'tsee MAX_VERTEX_OUTPUT_VECTORS or
> MAX_FRAGMENT_INPUT_VECTORS in the GLES 3 spec; only MAX_VARYING_VECTORS.
Brilliant. The API spec uses GL_MAX_*_COMPONENTS, but the GLSL built-in
variables are gl_Max*Vectors.
> BUT the description of MAX_VARYING_COMPONENTS in GLES3 says:
>
> "Number of components for output variables."
>
> So... OpenGL 3.2 makes no sense, and OpenGL ES 3.0 seems self
> contradictory. The core problem seems to be the way that each API (and
> each driver) counts gl_Position and gl_FragCoord. Some say it's
> counted, some say it's not counted, and some say it might be counted.
> Our existing infrastructure may not be sufficient to handle all
> combinations of those cases.
>
>
> I've spent a while digging through the specs, and I actually don't think
> it's quite as complicated or counterintuitive as it sounded at first.
>
> First of all, we don't need to worry about the distinction between
> COMPONENTS and VECTORS, because MAX_foo_COMPONENTS always equals
> MAX_foo_VECTORS * 4. Similarly, there's no need to distinguish between
> MAX_VARYING_COMPONENTS and MAX_VARYING_FLOATS.
Right. In fact, the differing names have the same enum values.
> As for the question of whether gl_Position and gl_FragCoord count
> against these limits, all GL specs since 2.0, and all GLES specs since
> 2.0 seem to agree that gl_Position is *not* counted for
> MAX_VARYING_COMPONENTS, however MAX_*_OUTPUT_COMPONENTS and
> MAX_*_INPUT_COMPONENTS count *all* inputs and outputs. I think
> reasonable to infer that the spec writers probably intended for the same
> to apply to gl_FragCoord and gl_FrontFacing (namely, they don't count
> against MAX_VARYING_COMPONENTS, but the do count against
> MAX_FRAGMENT_INPUT_COMPONENTS).
The OpenGL 3.1 spec says:
"The transformed vertex position (gl_Position) is not a varying
variable and does not count against [MAX_VARYING_COMPONENTS]."
However, the OpenGL ES 3.0 and OpenGL 3.2 (and later) specs say:
"When a program is linked, all components of any varying and
special variable written by a vertex shader will count against
[MAX_VERTEX_OUTPUT_COMPONENTS]."
And
"This limit is given by the value of the implementation-dependent
constant MAX_VARYING_COMPONENTS. Each varying or special variable
component used as either a vertex shader output or fragment
shader input count against this limit, except for the components
of gl_Position."
And
"When a program is linked, all components of any varying and
special variable read by a fragment shader will count against
[MAX_FRAGMENT_INPUT_COMPONENTS]."
MAX_VARYING_COMPONENTS was reduced from 64 to 60 in 3.2 because, as I
recall, some vendor (AMD?) had to use varying space for gl_FragCoord.
If gl_FragCoord wasn't read, gl_Position didn't need any space. I
/think/. Those discussions were a loooong time ago.
The stage-specific values are 64 on desktop GL because gl_Position and
gl_FragCoord are counted. I don't know why
MAX_FRAGMENT_INPUT_COMPONENTS is only 60 on ES. Given the different
counting, 64 seems to be the correct value if MAX_VARYING_COMPONENTS is
64. *shrug*
> Interestingly, ARB_vertex_shader doesn't specifically mention that
> gl_Position is excluded from MAX_VARYING_FLOATS, but it defines
> MAX_VARYING_FLOATS as the number of "interpolators" that are available,
> so I think it's a reasonable interpretation that gl_Position is not
> intended to be counted (especially given that this is the interpretation
> that the GL spec authors chose when promoting the extension into GL 2.0).
>
> Note that all the specs allow for the possibility that device-dependent
> optimizations may allow for more than the advertised number of
> inputs/outputs/varyings to be supported in some circumstances, so if a
> certain piece of hardware has dedicated input/output locations for
> certain variables, that's not a problem; it simply means that in some
> situations the driver may be able to successfully compile and link a
> shader that isn't strictly guaranteed by the spec to work.
>
> So it seems to me that there's a single consistent interpretation:
> clients may assume that MAX_VARYING_{FLOATS,COMPONENTS,VECTORS} applies
> just to things that are truly varyings (gl_Position, gl_FragCoord, and
> gl_FrontFacing are exempted), but to be safe, clients must assume that
> MAX_*_OUTPUT_COMPONENTS and MAX_*_INPUT_COMPONENTS apply to all shader
> inputs/outputs. However, implementations are free to choose not to
> count certain inputs/outputs against these limits, causing them to
> successfully compile and link shaders that would otherwise fail.
>
> (There is the minor wrinkle that certain implementations have a
> hardware-imposed limit of 64 on the number of vertex output components
> (including gl_Position), so they aren't strictly able to support GL
> 3.0-3.1's requirement that MAX_VARYING_COMPONENTS >= 64. I'm not sure
> if Mesa supports any of these implementations; but if it does, I think
> we can finesse that issue).
>
> In the end, I opted to use VertexProgram.MaxOutputComponents because
> MAX_VARYING_FLOATS was added by GL_ARB_vertex_shader.
>
> I guess I'm not sure what the "right" answer actually is now. :(
>
>
> Now that I've spent a day thinking about all this, it seems to me that
> Mesa front end shouldn't ever try to infer MAX_VARYING_COMPONENTS from
> MAX_VERTEX_OUTPUT_COMPONENTS and MAX_FRAGMENT_INPUT_COMPONENTS, because
> the relationship between them depends on exactly what the hardware
> limitations are. For example, once my 128-varyings patches land, Mesa
> on i965/gen6+ will be able to support:
>
> MAX_VARYING_COMPONENTS 128
> MAX_VERTEX_OUTPUT_COMPONENTS 128
> MAX_FRAGMENT_INPUT_COMPONENTS 128
>
> because the hardware has dedicated locations for gl_Position,
> gl_FragCoord, and gl_FrontFacing. But implementations that don't have
> those dedicated locations might support as little as:
>
> MAX_VARYING_COMPONENTS 120
> MAX_VERTEX_OUTPUT_COMPONENTS 128
> MAX_FRAGMENT_INPUT_COMPONENTS 128
>
> So I think the back-end should just specify all three of these values
> independently, and Mesa should expose them to the client without
> applying any further math to them (other than the factor of 4 to convert
> between component and vector counts).
I think, unfortunately, you are correct. I'm going to push the first 10
patches in the series, and I'll respin the last 7.
> Another question which we haven't really addressed is how Mesa's front
> end linker should check these limits, given the fact that some
> implementations have dedicated locations for certain shader
> inputs/outputs. I have a few ideas about this, but it's probably
> something that we should save for a future patch series.
Maybe the 39th time will be the charm. :( The last time this came up
was w.r.t. gl_Color and gl_SecondaryColor. Most (all?) SM2 hardware
(i915, r300, and probably others) have special slots that can be used
for *clamped* fragment shader inputs. So, gl_Color can use those slots
if the API setting of CLAMP_VERTEX_COLOR is TRUE. This control is added
by the GL_ARB_color_buffer_float extension and OpenGL 3.0
I think we need a flag for each special variable that says whether or
not it is counted. I think Marek implemented something like this for
gl_Color.
_______________________________________________
mesa-dev mailing list
mesa-dev@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/mesa-dev
