Use new GPU_legacy_support() function.
Determine GLSL version once instead of per shader.
For Texture Buffers, allow ARB or EXT version of the extension. Either
one will do.
GLSL 130, 140, 150 with extensions as needed.
Similar logic to my recent gpu_extensions changes.
Partially fixes T46706. Matcaps now work with OpenSubdiv, as do basic
materials. Anything with UV coordinates is still broken.
Disable Intel cards for until we'll go to the root of the issue of the crash.
This will take a bit, so being so close to the release we go safe and disable
unstable GPU, so blender at least doesn't crash.
This could be bypassed by setting OPENSUBDIV_ALLOW_INTEL environment variable.
It's hopefully no longer needed, at least not needed for as long as
single ptex face corresponds to a single patch which should be always
correct for uniform subdivisions as far as i know.
Use vertex varying data which gives better approximation of normals.
Still not ideal but should be closer for higher poly meshes to correct
normal.
The only way to have proper smooth normals seems to be to implement
patch evaluation in tessellation shader, but that's a bit PITA with
current GLSL usage in our draw code.
This includes C-API bindings in intern/opensubdiv and CMAke module
which finds the OpenSubdiv library. This filea are not in use so
far, making it a separate commit to make actual integration commit
more clear.
