Hey Alex! An updated explainer is now hosted at https://github.com/gpuweb/gpuweb/blob/main/proposals/primitive-index.md. It's still fairly brief because this is a relatively small feature.
--Brandon On Wed, Sep 3, 2025 at 7:13 AM Alex Russell <[email protected]> wrote: > Thanks for this, Brandon. > > As you know, the collateral we need to go first is much higher than when > closing compatibility gaps. > > This explainer doesn't indicate why anyone needs the feature, show the > before/after state of example code, or discuss considered alternatives. I'm > inclined to support the feature, but can't without more to go on. Can you > produce and updated explainer with the various things we usually expect to > see? > > Best, > > Alex > On Wednesday, August 27, 2025 at 7:17:40 PM UTC+1 Brandon Jones wrote: > >> Apologies! We're currently trying to decide where docs like that should >> live after we move them out of experimental status. In the meantime you can >> see the historical copy of the explainer here: >> https://dawn.googlesource.com/dawn/+/2819d509eff7e314e5ebce15cc3a7cb13370a505/docs/tint/extensions/chromium_experimental_primitive_id.md >> >> (Note that at the time the explainer was written the feature was going to >> be named primitive_id, the rename to primitive_index was a relatively late >> change by the working group.) >> >> --Brandon >> >> On Wed, Aug 27, 2025 at 1:02 AM Daniel Bratell <[email protected]> >> wrote: >> >>> The Explainer link is a 404 or has restricted access. We need the >>> explainer to be public. >>> >>> /Daniel >>> On 2025-08-25 10:56, Yoav Weiss (@Shopify) wrote: >>> >>> Can you request reviews for security/privacy/etc in chromestatus? >>> >>> On Fri, Aug 22, 2025 at 10:16 PM Chromestatus < >>> [email protected]> wrote: >>> >>>> Contact emails [email protected] >>>> >>>> Explainer >>>> https://dawn.googlesource.com/dawn/+/refs/heads/main/docs/tint/extensions/chromium_experimental_primitive_id.md >>>> >>>> Specification >>>> https://gpuweb.github.io/gpuweb/#dom-gpufeaturename-primitive-index >>>> >>>> Summary >>>> >>>> This feature adds a new optional capability to WebGPU that exposes a >>>> new WGSL shader builtin, 'primitive_index'. This builtin provides a >>>> per-primitive index to fragment shaders on supported hardware, similar to >>>> the existing vertex_index and instance_index builtins. The primitive index >>>> is useful for advanced graphical techniques, such as virtualized geometry. >>>> >>>> >>>> Blink component Blink>WebGPU >>>> <https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3EWebGPU%22> >>>> >>>> Search tags webgpu <http:///features#tags:webgpu>, primitive >>>> <http:///features#tags:primitive> >>>> >>>> TAG review None >>>> >>>> TAG review status Pending >>>> >>>> Risks >>>> >>>> >>>> Interoperability and Compatibility >>>> >>>> Little to none. It's a fairly minor feature that all implementors have >>>> voiced support for. The feature is optional and support for it must be >>>> explicitly queried through the standard WebGPU supported features >>>> mechanism. Some hardware doesn't expose it yet, so developers need to >>>> structure their apps to have a fallback path anyway. >>>> >>>> >>>> *Gecko*: No signal >>>> >>>> *WebKit*: No signal >>>> >>>> *Web developers*: No signals >>>> >>>> *Other signals*: >>>> >>>> Ergonomics >>>> >>>> None. >>>> >>>> >>>> Activation >>>> >>>> None. >>>> >>>> >>>> Security >>>> >>>> None. >>>> >>>> >>>> WebView application risks >>>> >>>> Does this intent deprecate or change behavior of existing APIs, such >>>> that it has potentially high risk for Android WebView-based applications? >>>> >>>> None >>>> >>>> >>>> Debuggability >>>> >>>> WGSL shader feature. Shaders generally lack debugging support in >>>> browsers. >>>> >>>> >>>> Will this feature be supported on all six Blink platforms (Windows, >>>> Mac, Linux, ChromeOS, Android, and Android WebView)? Yes >>>> >>>> Feature is widely supported and has equivalents in all Native APIs that >>>> WebGPU is implemented on top of. Some older hardware lacks ability to >>>> report the value, which is why it's an optional feature. >>>> >>>> >>>> Is this feature fully tested by web-platform-tests >>>> <https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md> >>>> ? No >>>> >>>> WebGPU CTS tests are a WIP: https://github.com/gpuweb/cts/pull/4435 >>>> >>>> >>>> Flag name on about://flags enable-unsafe-webgpu >>>> >>>> Finch feature name None >>>> >>>> Non-finch justification None >>>> >>>> Rollout plan Will ship enabled for all users >>>> >>>> Requires code in //chrome? False >>>> >>>> Tracking bug https://issues.chromium.org/issues/342172182 >>>> >>>> Estimated milestones >>>> >>>> No milestones specified >>>> >>>> >>>> Anticipated spec changes >>>> >>>> Open questions about a feature may be a source of future web compat or >>>> interop issues. Please list open issues (e.g. links to known github issues >>>> in the project for the feature specification) whose resolution may >>>> introduce web compat/interop risk (e.g., changing to naming or structure of >>>> the API in a non-backward-compatible way). >>>> None >>>> >>>> Link to entry on the Chrome Platform Status >>>> https://chromestatus.com/feature/6467722716250112?gate=4665168428662784 >>>> >>>> This intent message was generated by Chrome Platform Status >>>> <https://chromestatus.com>. >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "blink-dev" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to [email protected]. >>>> To view this discussion visit >>>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/68a8d032.050a0220.8fac8.a218.GAE%40google.com >>>> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/68a8d032.050a0220.8fac8.a218.GAE%40google.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "blink-dev" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To view this discussion visit >>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAOmohS%2BP74WaABq%2BdYeukKDUvBazGrTk7SnT5QLRj09ZZwrE1w%40mail.gmail.com >>> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAOmohS%2BP74WaABq%2BdYeukKDUvBazGrTk7SnT5QLRj09ZZwrE1w%40mail.gmail.com?utm_medium=email&utm_source=footer> >>> . >>> >>> -- You received this message because you are subscribed to the Google Groups "blink-dev" group. 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