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Reformat builtins table #5092

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Reformat builtins table 
Separate the builtins by stage and input/output as it's
arguably less confusiung.

Note: This only separates the table. It would be nice to also
separate the documentation so that vertex position links to
a different place than fragment position and sample_mask
input links to different place than sample_mask output.
That change can happen in another PR.

Issue #5081

Note: Other GPU API specs no not combine inputs and outputs
from multiple stages into one.

* [GLSL](https://registry.khronos.org/OpenGL/specs/es/3.1/GLSL_ES_Specification_3.10.withchanges.pdf),
  sections (7.1.1, 7.1.2, 7.1.3).

* [HLSL](https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-semantics)

* [MSL](https://developer.apple.com/metal/Metal-Shading-Language-Specification.pdf)
  sections 5.2.3.1, 5.2.3.3, 5.2.3.4, 5.2.3.5, 5.2.3.6
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@greggman
greggman committed Feb 28, 2025
commit 95075a612b835cfe2fad79f5c620c85d71ce60b5
125 changes: 70 additions & 55 deletions wgsl/index.bs
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Expand Up @@ -9227,107 +9227,122 @@ Note: The [=built-in values/position=] built-in is both an output of a vertex sh

Collectively, built-in input and built-in output values are known as <dfn noexport>built-in values</dfn>.

The following table summarizes the available built-in values.
The following tables summarizes the available built-in values by stage.
Each is a [=built-in value name-token|built-in value name=] [=token=] for a [=built-in value=].
Each is described in detail in subsequent sections.

<table class='data'>
<caption>Built-in input and output values</caption>
<caption>Built-in Vertex stage inputs</caption>
<thead>
<tr><th>Name<th>Stage<th>Direction<th>Type<th>[=Extension=]
<tr><th>Name<th>Type<th>[=Extension=]
</thead>

<tr><td>[=built-in values/vertex_index=]
<td>vertex
<td>input
<td>u32
<td rowspan=2>
<td>

<tr><td>[=built-in values/instance_index=]
<td>vertex
<td>input
<td>u32
<td>
</table>

<table class='data'>
<caption>Built-in Vertex stage outputs</caption>
<thead>
<tr><th>Name<th>Type<th>[=Extension=]
</thead>

<tr><td>[=built-in values/clip_distances=]
<td>vertex
<td>output
<td>array&lt;f32, N&gt; (`N` &le; `8`)
<td>[=extension/clip_distances=]

<tr><td rowspan=2>[=built-in values/position=]
<td>vertex
<td>output
<tr><td>[=built-in values/position=]
<td>vec4&lt;f32&gt;
<td rowspan=12>
<td>

<tr>
<td>fragment
<td>input
</table>

<table class='data'>
<caption>Built-in Fragment stage inputs</caption>
<thead>
<tr><th>Name<th>Type<th>[=Extension=]
</thead>

<tr><td>[=built-in values/position=]
<td>vec4&lt;f32&gt;
<td>

<tr><td>[=built-in values/front_facing=]
<td>fragment
<td>input
<td>bool

<tr><td>[=built-in values/frag_depth=]
<td>fragment
<td>output
<td>f32
<td>

<tr><td>[=built-in values/sample_index=]
<td>fragment
<td>input
<td>u32
<td>

<tr><td rowspan=2>[=built-in values/sample_mask=]
<td>fragment
<td>input
<tr><td>[=built-in values/sample_mask=]
<td>u32
<td>

<tr>
<td>fragment
<td>output
<tr><td>[=built-in values/subgroup_invocation_id=]
<td>u32
<td>[=extension/subgroups=]

<tr><td>[=built-in values/subgroup_size=]
<td>u32
<td>[=extension/subgroups=]

</table>

<table class='data'>
<caption>Built-in Fragment stage outputs</caption>
<thead>
<tr><th>Name<th>Type<th>[=Extension=]
</thead>

<tr><td>[=built-in values/frag_depth=]
<td>f32
<td>

<tr><td>[=built-in values/sample_mask=]
<td>u32
<td>

</table>

<table class='data'>
<caption>Built-in Compute stage inputs</caption>
<thead>
<tr><th>Name<th>Type<th>[=Extension=]
</thead>

<tr><td>[=built-in values/local_invocation_id=]
<td>compute
<td>input
<td>vec3&lt;u32&gt;
<td>

<tr><td>[=built-in values/local_invocation_index=]
<td>compute
<td>input
<td>u32
<td>

<tr><td>[=built-in values/global_invocation_id=]
<td>compute
<td>input
<td>vec3&lt;u32&gt;
<td>

<tr><td>[=built-in values/workgroup_id=]
<td>compute
<td>input
<td>vec3&lt;u32&gt;
<td>

<tr><td>[=built-in values/num_workgroups=]
<td>compute
<td>input
<td>vec3&lt;u32&gt;
<td>

<tr><td rowspan=2>[=built-in values/subgroup_invocation_id=]
<td>compute
<td rowspan=2>input
<td rowspan=2>u32
<td rowspan=2>[=extension/subgroups=]
<tr><td>fragment

<tr><td rowspan=2>[=built-in values/subgroup_size=]
<td>compute
<td rowspan=2>input
<td rowspan=2>u32
<td rowspan=2>[=extension/subgroups=]
<tr><td>fragment
<tr><td>[=built-in values/subgroup_invocation_id=]
<td>u32
<td>[=extension/subgroups=]

<tr><td>[=built-in values/subgroup_size=]
<td>u32
<td>[=extension/subgroups=]
</table>

<div class='example wgsl global-scope' heading="Declaring built-in values">
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