[Mesa-dev] [PATCH] glsl: initialize samplers mapping with 0

[Kenneth Graunke]

On 04/28/2012 12:24 PM, Vadim Girlin wrote:
> On Sat, 2012-04-28 at 11:42 -0700, Kenneth Graunke wrote:
>> On 04/28/2012 11:20 AM, Vadim Girlin wrote:
>>> According to GLSL 1.30 specification, initial value for all uniforms
>>> without initializer is 0.  Some applications rely on this behaviour,
>>> e.g. google's MapGL doesn't set all sampler uniforms.
>>>
>>> (see https://bugs.freedesktop.org/show_bug.cgi?id=49088 )
>>>
>>> Signed-off-by: Vadim Girlin<vadimgirlin at gmail.com>
>>> ---
>>>
>>> Tested with r600g only - no regressions.
>>
>> Awesome find!  I was at a complete loss here. :)
>>
>> It turns out this is in the 1.20 spec too; it looks like 1.10 doesn't
>> say (but that isn't too surprising).  I might add a comment:
>>
>> /* From the GLSL 1.20 specification, page 24, section 4.3.5 "Uniform":
>>    * "The link time initial value is either the value of the variable's
>>    *  initializer, or 0 if no initializer present.  Sampler types cannot
>>    *  have initializers."
>>    */
>>
>> Also, do you really need the memsets in ir_to_mesa and st_glsl_to_tgsi?
>>    Everything should go through the linker, so that seems somewhat
>> redundant.  I tested with just the link_uniforms change and that was
>> enough to fix MapsGL on i965/Sandybridge.
>
> Without the memset in the st_glsl_to_tgsi firefox crashed with MapGL.
> Probably some code in the state tracker relies on the synchronized
> values of the SamplerUnits arrays in the gl_program and
> gl_shader_program. Also, _mesa_uniform function compares these arrays to
> check for update, and some piglit test failed due to the following
> problem:
>
> First array is initialized: 0, 0, 0, ...
> Second (without memset)	  : 0, 1, 2, ...
>
> The app calls Uniform1i to set sampler[1] to 1, so we do first[1]=1, but
> then it's equal with second[1] and update is not detected.
>
> Vadim

Ah, okay...I missed that one was operating on the gl_shader_program 
while the other was setting the parallel structure in the gl_program.

I can believe that you'd need that, then.