[Webkit-unassigned] [Bug 244152] New: use of gl_VertexId causes error compiling shader with Metal backend

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=244152

            Bug ID: 244152
           Summary: use of gl_VertexId causes error compiling shader with
                    Metal backend
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Mac (Intel)
                OS: macOS 12
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebGL
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: morem at gmx.de
                CC: dino at apple.com, kbr at google.com, kkinnunen at apple.com

Hi,

I get an error checking the link status of a WebGL2 shader program

"Internal error compiling shader with Metal backend"

Or if I call `gl.validateProgram` before checking the link status

"Program has not been successfully linked."


I don't have a minimal reproduction but tracked it down to the use of `gl_VertexId` and found a workaround. If I use it as is I get the above error but if I do `int(gl_VertexId)` everything works fine. I don't see this issue with Firefox or Chrome on Mac or Win.

I see the issue in Safari 16.0, 15.6 and earlier.


You can trigger the error in Mol* here: https://molstar.org/viewer/?debug-mode=1&emdb=EMD-14403


Best
Alexander

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