gl_shader: do not require GL_ARB_texture_float in shader

[illwieckz]

Do not require GL_ARB_texture_float in vertex shader, this is a vertex-only extension.

This is only for convenience, I get this error on both Mesa radeonsi and llvmpipe drivers when I downgrade the GL/GLSL version to test GLSL 1.20, using MESA_GL_VERSION_OVERRIDE=2.1 MESA_GLSL_VERSION_OVERRIDE=120 environment variables:

Warn: Source for shader program deformVertexes_0:
   0: #version 120 
   1: 
   2: #extension GL_ARB_gpu_shader5 : require
   3: #define HAVE_ARB_gpu_shader5 1
   4: #extension GL_ARB_shading_language_420pack : require
   5: #define HAVE_ARB_shading_language_420pack 1
   6: #extension GL_ARB_texture_float : require
   7: #define HAVE_ARB_texture_float 1
------------------^-------------------
0:7(12): error: extension `GL_ARB_texture_float' unsupported in vertex shader

I haven't got this error on actual GL 2.1 / GLSL 1.20 hardware I recently tested (Nvidia, Intel).

There may be other extensions that may be specific to fragment shaders, but they are probably just missing or unused with such GL version so I didn't faced other errors.

While moving other fragment-specific extensions to the fragment-specific list may be better, for “purity” and “just in case” concerns, it is actually not required to make the shaders buildable again on such test bed, so it's not in the scope of this PR.

[illwieckz]

I now consider it a driver bug. Now that I fixed the stupid double-return, it now complains that GL_ARB_texture_float is not supported in a fragment shader…

Warn: Source for shader program generic:
   0: #version 120 
   1: 
   2: #extension GL_ARB_gpu_shader5 : require
   3: #define HAVE_ARB_gpu_shader5 1
   4: #extension GL_ARB_shading_language_420pack : require
   5: #define HAVE_ARB_shading_language_420pack 1
   6: #extension GL_ARB_texture_gather : require
   7: #define HAVE_ARB_texture_gather 1
   8: #define HAVE_ARB_texture_rg 1
   9: #extension GL_ARB_uniform_buffer_object : require
  10: #define HAVE_ARB_uniform_buffer_object 1
  11: #extension GL_ARB_shader_storage_buffer_object : require
  12: #define HAVE_ARB_shader_storage_buffer_object 1
  13: #extension GL_ARB_texture_float : require
  14: #define HAVE_ARB_texture_float 1
------------------^-------------------
0:14(12): error: extension `GL_ARB_texture_float' unsupported in fragment shader

[slipher]

Maybe that extension name just shouldn't appear in GLSL directives? https://registry.khronos.org/OpenGL/extensions/ARB/ARB_texture_float.txt doesn't say anything about #extension, whereas, for example, https://registry.khronos.org/OpenGL/extensions/ARB/ARB_gpu_shader5.txt says

Shaders using the new functionality provided by this extension should enable thisfunctionality via the construct
#extension GL_ARB_gpu_shader5 : require (or enable)

[VReaperV]

I think slipher is right. Especially given that the specification says OpenGL 1.1 or EXT_texture is required, and 1.1 doesn't have shaders to begin with (excepting the use of the shader extensions, but the spec for GL_ARB_texture_float doesn't mention those).

[illwieckz]

OK, if I'm right, the current change prevents the require instruction to be printed.

At least it fixes the problem on my end.

[slipher]

LGTM