GPUExtensions: GL backend isolation

This is part of the Vulkan task T68990.

This commits changes a few things:
- Rename extensions to capabilities (but left the file name untouched).
- Cubemap mip render workaround detection is rewritten using gl
  commands to avoid using the GPU API before initialization.
- Put all the capabilities that are only relevant for the GL backend
  inside GLContext as static variables.
- Cleanup the names of the limit variables.
- Separate all GL related workaround search inside the GL module.

1 files changed, 3 insertions, 4 deletions

diff --git a/source/blender/gpu/opengl/gl_shader.cc b/source/blender/gpu/opengl/gl_shader.cc
index 9136a1d9714..f125afeb535 100644
--- a/source/blender/gpu/opengl/gl_shader.cc
+++ b/source/blender/gpu/opengl/gl_shader.cc
@@ -28,6 +28,7 @@
 #include "GPU_extensions.h"
 #include "GPU_platform.h"
 
+#include "gl_backend.hh"
 #include "gl_vertex_buffer.hh"
 
 #include "gl_shader.hh"
@@ -118,10 +119,8 @@ char *GLShader::glsl_patch_get(void)
   }
 
   /* Derivative sign can change depending on implementation. */
-  float derivatives[2];
-  GPU_get_dfdy_factors(derivatives);
-  STR_CONCATF(patch, slen, "#define DFDX_SIGN %1.1f\n", derivatives[0]);
-  STR_CONCATF(patch, slen, "#define DFDY_SIGN %1.1f\n", derivatives[1]);
+  STR_CONCATF(patch, slen, "#define DFDX_SIGN %1.1f\n", GLContext::derivative_signs[0]);
+  STR_CONCATF(patch, slen, "#define DFDY_SIGN %1.1f\n", GLContext::derivative_signs[1]);
 
   BLI_assert(slen < sizeof(patch));
   return patch;