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

[Vadim Girlin]

On Sat, 2012-04-28 at 13:02 -0700, Kenneth Graunke wrote:
> 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.
> 

BTW, it seems there is a patch from Ian for this issue on the list:

http://lists.freedesktop.org/archives/mesa-dev/2012-April/020767.html

Vadim