This is basically just the same atomic functions exposed by
ARB_shader_image_load_store, with one exception:
"highp float imageAtomicExchange(
coherent IMAGE_PARAMS,
float data);"
There's no float atomic exchange overload in the original
ARB_shader_image_load_store or GL 4.2, so this seems like new
functionality that requires specific back-end support and a separate
availability condition in the built-in function generator.
v2: Move image availability predicate logic into a separate static
function for clarity. Had to pull out the image_function_flags
enum from the builtin_builder class for that to be possible.
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
It's a bit more descriptive since it is the base type that you get when you
sample from it. Also, the next commit adds a bare "sampler" type and we
need glsl_type::sampler_type available for a public static member.
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
