[Mesa-dev] [PATCH 4/8] glsl: Add new builtins required by GL_ARB_sample_shading

[Kenneth Graunke]

On 10/15/2013 01:58 PM, Ian Romanick wrote:
> On 10/15/2013 01:50 PM, Anuj Phogat wrote:
>> On Tue, Oct 15, 2013 at 10:02 AM, Ian Romanick <idr at freedesktop.org> wrote:
>>> On 10/14/2013 10:12 AM, Anuj Phogat wrote:
>>>> @@ -789,6 +794,12 @@ builtin_variable_generator::generate_fs_special_vars()
>>>>        if (state->AMD_shader_stencil_export_warn)
>>>>           var->warn_extension = "GL_AMD_shader_stencil_export";
>>>>     }
>>>> +
>>>> +   if (state->ARB_sample_shading_enable) {
>>>> +      add_input(VARYING_SLOT_SAMPLE_ID, int_t, "gl_SampleID");
>>>> +      add_input(VARYING_SLOT_SAMPLE_POS, vec2_t, "gl_SamplePosition");
>>>> +      add_output(FRAG_RESULT_SAMPLE_MASK, array(int_t, 1), "gl_SampleMask");
>>>
>>> I don't see code anywhere in this patch series that correctly sizes this
>>> array.  I thought gl_SampleMask.length() == gl_NumSamples... except you
>>> can't use .length() on gl_SampleMask because the size can't be known at
>>> compile-time.  We should have a test that 'gl_SampleMask.length()' fails
>>> to compile. :)
>>>
>> I'll add a piglit compiler test for that.
>>
>>> The only other array that works like this is gl_TexCoord.  That array is
>>> sized to 0 (line 837 of builtin_variables.cpp).  I believe gl_SampleMask
>>> should do the same.
>>>
>> Yes, I noticed  gl_TexCoord is using array size of 0 and it works for
>> gl_SampleMask as well.  But, It generates same glsl ir with array size
>> of 0 or 1:
>> (declare (shader_out ) (array int 1) gl_SampleMask)
>>
>> what's the utility of using size 0?
>> I'll take care of rest of your comments in this patch.
> 
> Using size 0 is like writing
> 
> int gl_SampleMask[]; // unsized
> 
> in the shader.  Later during compilation, usually in linking, unsized
> arrays become sized.  Somewhere between generating the built-in variable
> and printing the IR a size is established for it.

Right, but gl_SampleMask is not an unsized array.  It's statically sized
based on your implementation's maximum supported number of color samples
(ceil(samples/32)), and this is totally known at compile time...

--Ken