Rule 8.2

Chapter 8, Functions and entry points Test

A vertex entry must return the position, as a bare vec4 or as a struct with a @builtin("position") field; a fragment entry returns one @location(0) value, a struct of render targets, or nothing.

The rule text and the parts under it are the compiler's own English, as the design document writes them.

Rationale

nothing can invent a position, and WGSL says so.

Derives from

Restrictions on Functions (“a vertex shader must return the position built-in output value”); surface §3.

How it is verified

Checked by a test. A test, a gate script or a CI workflow names this rule, and the traceability check fails when a file listed below stops naming it.

Where the rule says the compiler enforces it:

src/compiler/ts/entry-io.test.ts.

The files that verify it at commit 26de7be8, each at the first line that names the rule:

src/compiler/ts/entry-io.test.ts:17

Explained in

The sections of the surface document that explain this rule, at commit 26de7be8:

§3 Entries — function decorators and explicit builtins

Source

The rule at commit 26de7be8:

docs/language-design.md:618 (the design document)
reqs/rules/RULE-0802.md (its traceability item)

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