Move visualize_image function to util/piglit-util-gl.c

This function might be useful to develop new piglit test cases.

Signed-off-by: Anuj Phogat<anuj.phogat@gmail.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Add utility functions to convert a color value to srgb or linear color space

Signed-off-by: Anuj Phogat<anuj.phogat@gmail.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Use utility function piglit_srgb_to_linear()

Signed-off-by: Anuj Phogat<anuj.phogat@gmail.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Add new test for MRT alpha test

This test exercises alpha test with multiple render targets. This is one
part of FDO #67864.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
ARB_texture_gather: add initial execution test

This test exercises combinations of:
- Shader stage vs/fs
- Offsetting
- Component count, up to implementation-defined limit
- Swizzling
- Unsigned normalized vs float type

The test works by numbering the texels, and ensuring that the four
texels sampled by textureGather*() are those we expect.

Not exercised yet:
- Integer textures
- Samplers other than sampler2D
- Other interesting internalformats [DEPTH_COMPONENT, etc]
- Addressing modes other than WRAP.

V2: - Use textureSize rather than hardcoding size in shader;
    - Use piglit_build_simple_program
    - Whitespace tidyups

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>