[Piglit] [RFC] Proposed changes to shader_runner

[Ian Romanick]

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I'm considering making a couple changes to shader_runner, but I want to
solicit feedback before I do.

I'm finishing up some code for Mesa's new GLSL compiler that does
processing on loops.  I want to create some additional "tricky" loop
tests to make sure some of the corner cases are handled correctly.  One
of the tests has a shader like the one below.  I want to set i1 to 0 and
i2 to 5.  If the dependency handling is correct, the shader will produce
green.  If it is not correct, the shader will produce red.

uniform int i1;
uniform int i2;
uniform float f;

void main()
{
  int c = i1;
  int i;
  float o = f;

  i = c;
  c = i2;
  while (i < 5) {
    o += 0.2;
    i++;
  }

   gl_FragColor = vec4(1.0 - (o / 2.0), o / 2.0, 0.0, 1.0);
}

The problem is that the compiler (correctly) optimizes i2 away.  The
call to glGetUniformLocation in shader_runner fails, and the test
aborts.  Nvidia's implementation does the same.

I want to change the error check in shader_runner to drop uniforms that
return -1 from glGetUniformLocation.  The problem is that this error
check has helped me (and presumably others) catch errors in their tests.
 Should I change it to emit a warning in the non-auto case?

The other option is to just use the GLSL 1.20 uniform initializer
syntax, but this won't work with sampler uniforms (when we add texture
support to shader runner).

The other change that I want to make, and I know Eric has talked about
doing this too, is to "ignore" checks for "GL >= 2.0".  When
shader_runner sees "GL >= 2.0" it will interpret it as a request for
OpenGL 2.0 or GL_ARB_shader_objects, GL_ARB_vertex_shader, and
GL_ARB_fragment_shader.  Other than potentially making the code messy, I
don't see any ill effects of this.

The main upshot is that those few implementations that can do GLSL but
lack some other OpenGL 2.0 features (i.e., i915 which lack occlusion
query) can play.

Opinions?
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