8dee08996e
This avoid having to guards functions that are only available in fragment shader stage. Calling the function inside another stage is still invalid and will yield a compile error on Metal. The vulkan and opengl glsl patch need to be modified per stage to allow the fragment specific function to be defined. This is not yet widely used, but a good example is the change in `film_display_depth_amend`. Rel #137261 Pull Request: https://projects.blender.org/blender/blender/pulls/138280