[Webkit-unassigned] [Bug 240975] New: Odd WebGL framebuffer issues on M1 macs

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=240975

            Bug ID: 240975
           Summary: Odd WebGL framebuffer issues on M1 macs
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Mac (Apple Silicon)
                OS: macOS 12
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebGL
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: enowak at ptc.com
                CC: dino at apple.com, kbr at google.com, kkinnunen at apple.com

Created attachment 459791

  --> https://bugs.webkit.org/attachment.cgi?id=459791&action=review

Incorrect behavior

In Safari 15.4 on M1 macs we are seeing rendering issues in our web application, Onshape.  I verified this on a recent WebKit build (251013 at main).

To reproduce the issue:
- Find an M1 Macbook (video was produced on a Macbook Air M1, 2020)
- Start up Safari 15.4
- Navigate to: https://cad.onshape.com/documents/ffedc1dc4bb9c3dc06004002/w/451e7b9d956f374a17b9118f/e/1ffdf0650483be1b8f5c255e
- Wait for page to load
- Move the mouse pointer over the cube that is visible in the WebGL canvas.  Note that the faces of the cube highlight as you move the pointer over them.
- Use the trackpad or scrollwheel to scroll while the mouse pointer is over the canvas.  This will cause the view to zoom in and out.  Alternatively, click in the canvas with the right mouse button and drag within the canvas.  This will cause the view to rotate.
- If these sorts of view manipulations are performed while a graphical highlight is visible, then the background shaded graphics will not update, however the highlight layer does display as expected.  (See "Incorrect behavior" video)

In other browsers and systems the background shaded graphics will update correctly as the view is manipulated.

I expect there is an issue at a fairly low level in either Safari's WebGL implementation, or in the display driver.  Highlights are achieved by rendering a subset of geometry in a highlight style to an off-screen framebuffer.  This is then composited on top of the main framebuffer for the WebGL context.  It looks as though something is going on with the framebuffer management.

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