[Webkit-unassigned] [Bug 278926] Additive colors broken with WebGL canvas and premultiplied alpha compositing

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=278926

--- Comment #1 from Kimmo Kinnunen <kkinnunen at apple.com> ---
> I'm testing on macOS 14.6.1 on a M2 Max MBP myself. In our testing we haven't been able to reproduce the issue on any iOS devices yet.

FWIW, it seems to work on macOS 15 Sequoia beta.

> Not sure if this use case is covered by the HTML or WebGL standards, or which standard even applies, given that this falls somewhere between both worlds, but the 

I think this should be defined by the CSS compositing model.

I don't know if it is supposed to work the way it works now in macOS 15/iOS, the way you expect.. I'll ask around.


> HTML living standard at least appears to acknowledge the possibility of drawing premultiplied alpha additive colors into a WebGL canvas: https://html.spec.whatwg.org/#premultiplied-alpha-and-the-2d-rendering-context

This is specifying how the premultiplied WebGL is drawn to (premultiplied) 2D Context.
It's a good and insightful explanation of the situation, though.

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