[Webkit-unassigned] [Bug 261270] New: Texture swizzling disabled in ANGLE on iOS simulator

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=261270

            Bug ID: 261270
           Summary: Texture swizzling disabled in ANGLE on iOS simulator
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: ANGLE
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: kkinnunen at apple.com
                CC: dino at apple.com, kbr at google.com, kkinnunen at apple.com

Fails:
webgl/2.0.y/conformance2/extensions/webgl-stencil-texturing.html

Alexey writes:
The iOS-16-Simulator-WK2-Tests-EWS failure in conformance2/extensions/webgl-stencil-texturing.html that blocks https://github.com/WebKit/WebKit/pull/17476 caused by the following:
That test asserts sampling both depth and stencil values.
The ES 3.0 spec defines sampled depth as [D, 0, 0, 1.0].
MSL spec explicitly says that green, blue, and alpha values are undefined. In practice it's either [D, 0, 0, 1.0] or [D, D, D, 1.0].
ANGLE uses texture swizzling to enforce ES 3.0 values for unused channels.
Texture swizzle support has been force-disabled on iOS Simulator during the initial WebKit-to-Chromium ANGLE upstreaming.
https://chromium-review.googlesource.com/c/angle/angle/+/2950067/33/src/libANGLE/renderer/metal/DisplayMtl.mm#954

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