[Mesa-dev] [PATCH 1/9] compiler: Add new system value SYSTEM_VALUE_BASE_VERTEX_ID

[Neil Roberts]

Kenneth Graunke <kenneth at whitecape.org> writes:

> We have a number of similar names now:
>
>    SYSTEM_VALUE_BASE_VERTEX
>    SYSTEM_VALUE_BASE_VERTEX_ID
>    SYSTEM_VALUE_VERTEX_ID
>    SYSTEM_VALUE_VERTEX_ID_ZERO_BASE
>
> BASE_VERTEX and BASE_VERTEX_ID are really similar names, and honestly
> either one seems like it could be the name for gl_BaseVertex.  I'm
> afraid it would be easy to mix them up by mistake.  IMHO, it would be
> nice to pick a different word, just to keep some distinction between
> the two fairly related concepts...
>
> Perhaps SYSTEM_VALUE_FIRST_VERTEX...?  That's only half the meaning,
> but it at least uses a different word, and makes you think "do I want
> BASE_VERTEX or FIRST_VERTEX?"

Yes, naming this thing is really difficult. I’m not sure if you noticed,
but for Vulkan, the BaseVertex builtin should actually have the value of
BASE_VERTEX_ID unlike GL. So if we rename BASE_VERTEX to something
without “base vertex” in it then it will still be confusing for Vulkan.
So effectively the descriptive names are like:

SYSTEM_VALUE_BASE_VERTEX_ON_GL_BUT_NOT_VULKAN
SYSTEM_VALUE_BASE_VERTEX_ON_VULKAN_OR_OFFSET_FOR_VERTEX_ID_ON_GL

I’m not sure whether that’s enough of an argument against FIRST_VERTEX
though, so personally I don’t really mind either way.

Antia, what do you think?

Regards,
- Neil
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