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

[Ian Romanick]

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.