WebGPU: `subgroup_id` feature

Category: Graphics
Type: New or changed feature
Status: Proposed (Chrome Proposed)
Intent stage: None

Breaking change: No
Enterprise impact: None
Chromium flag: Enable Unsafe WebGPU
Spec maturity: Published standard
Web Platform Tests: Yes

WPT details: WebGPU/WGSL have a conformance test suite (https://github.com/gpuweb/cts) that is regularly pulled into Chromium and part of the testing of Dawn/Tint in Chromium. While the CTS can be embedded in WPT, the WebGPU team opted to keep it separate in Chromium testing to use a customized harness for robustness and performance. CTS coverage for the feature was added here: https://github.com/gpuweb/cts/pull/4487

Summary

Functionality added to the WebGPU spec after its first shipment in a browser. The `subgroup_id` and `num_subgroups` built-in values are now available when the subgroups extension is enabled.

Motivation

The `subgroup_id` and `num_subgroups` built-in values are now available when the subgroups extension is enabled. This improves the process of scheduling work across subgroups in WebGPU compute shaders.

Standards & signals

Specification: https://www.w3.org/TR/WGSL/#language_extension-subgroup_id
Firefox: No signal
Safari: Closed Without a Position
Web developers: No signals
Tracking bug: https://crbug.com/454654255

Ecosystem

Web Platform Tests: https://wpt.fyi/results/?q=webgpu%2FWGSL
Chrome Platform Showcase: https://chrome-platform-showcase.paulkinlan-ea.deno.net/features
GenDN reference: https://gendn.paulkinlan-ea.deno.net/features
chrome.dev demos search: https://www.google.com/search?q=site%3Achrome.dev+WebGPU%3A%20%60subgroup_id%60%20feature
MDN Web Docs: https://developer.mozilla.org/en-US/search?q=WebGPU%3A%20%60subgroup_id%60%20feature
Baseline status: https://webstatus.dev/?q=WebGPU%3A%20%60subgroup_id%60%20feature

Explainers: https://github.com/gpuweb/gpuweb/blob/486577ae07e0fe3c433859499a1b558ee7c5275b/proposals/subgroup-id.md

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