[Webkit-unassigned] [Bug 239015] REGRESSION (Safari 15.4) Performance regression after uploading WebGL buffers

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=239015

--- Comment #10 from Kimmo Kinnunen <kkinnunen at apple.com> ---
The slowdown seems to come from the primitive restart index cache update.

WebKit's restart cache refactor was copied to ANGLE but not verbatim. The is cache truthiness flag meaning got inverted and the memory usage optimisation in clearConversionBuffers was lost.

https://bugs.webkit.org/show_bug.cgi?id=227451
https://chromium-review.googlesource.com/c/angle/angle/+/3331675

It appears that the dummy workaround would be to make a dummy sub buffer update to the element buffer after the first draw.

- First draw updates the indexType to be correct (invalid enum -> draw buffer element type)
- dummy subbuffer update marks the cache dirty

since the "cache is dirty" state currently means "don't update the cache", it will skip the cache update.

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