[PATCH vkd3d 3/5] vkd3d-shader/spirv: Send descriptor offsets via a shader parameter.

[Henri Verbeet]

On Thu, 25 Nov 2021 at 04:32, Conor McCarthy <cmccarthy at codeweavers.com> wrote:
> November 25, 2021 4:36 AM, "Henri Verbeet" <hverbeet at gmail.com> wrote:
> > In the case of descriptor offsets, what's missing is support for
> > specifying arrays. That may simply be a matter of adding something
> > like "const uint32_t *u32_array;" to the union in the
> > vkd3d_shader_parameter_immediate_constant structure. The
> > specialisation constant path should work fine as-is in terms of API,
> > but probably needs some work in terms of SPIR-V generation.
>
> Should this use a new helper for getting an immediate constant from an array, something like:
>
>     vkd3d_dxbc_compiler_get_uint_shader_array_parameter(struct vkd3d_dxbc_compiler *compiler,
>             enum vkd3d_shader_parameter_name name, unsigned int index)
>
> Plus a data type check in vkd3d_dxbc_compiler_emit_uint_shader_parameter().
>
Something along those lines. I think
vkd3d_dxbc_compiler_get_constant_uint() should work fine for arrays,
the caller can just pass something like
"parameter->u.immediate_constant.u.u32_array[index]". We'd want an
indexed variant of vkd3d_dxbc_compiler_emit_uint_shader_parameter()
though, which we could then use in
vkd3d_dxbc_compiler_get_descriptor_index().

> I don't see a need to support specialisation constant arrays. We can just emit a compiler error if the UINT32_ARRAY data type is specified for a specialisation constant.

We could, but it's weird in terms of API consistency. From the point
of view of a user of the API, there doesn't seem to be a good reason
specialisation constant arrays wouldn't/shouldn't/couldn't be
supported. It doesn't seem terribly hard to add either.