Adds API to allow usage of specialization constants in shaders.
Specialization constants are dynamic runtime constants which can
be compiled into a shader pipeline state object (PSO) to improve
runtime performance by reducing shader complexity through
shader compiler constant-folding.
This API allows specialization constant values to be specified
along with a default value if no constant value has been declared.
Each GPU backend is then responsible for caching PSO permutations
against the current specialization configuration.
This patch adds support for specialization constants in the
Metal backend and provides a generalised high-level solution
which can be adopted by other graphics APIs supporting
this feature.
Authored by Apple: Michael Parkin-White
Authored by Blender: Clément Foucault (files in gpu/test folder)
Pull Request: https://projects.blender.org/blender/blender/pulls/115193
335d3a1b75