[Webkit-unassigned] [Bug 219851] New: WebGL Float Texture Blending Regression

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=219851

            Bug ID: 219851
           Summary: WebGL Float Texture Blending Regression
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Mac (Intel)
                OS: macOS 10.15
            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

Created attachment 416152

  --> https://bugs.webkit.org/attachment.cgi?id=416152&action=review

A run-through of the reproduction steps from the bug description

Following the release of Safari 14, we have had several users complain that an aspect of our WebGL application has stopped functioning.  We use float textures to do real-time sectioning of 3D geometry and render flat "end caps" on the solid geometry.  We also employ float texture blending to achieve this effect. As of the Safari 14 release, these endcaps no longer appear.

To reproduce:
1. Navigate to https://cad.onshape.com/documents/21528514dbb278dfb84b48fc/w/b8e3c69807c266318a9e26fe/e/15c030164c537c1eec47b4b6 and wait for graphics to appear
2. From the cube drop-down menu towards the upper right, select "Named views"
3. In the "Named views" dialog that pops up, select "Section" from the "Select a view" dropdown 
Notice that there is empty space where you would expect a flat intersection of the cube to be.  This works properly in Firefox and Chrome on the same system.

See attached video for run-through of reproduction steps.

Interestingly, the EXT_float_blend conformance test is also failing in Safari 14:
https://www.khronos.org/registry/webgl/sdk/tests/conformance/extensions/ext-float-blend.html?webglVersion=1&quiet=0&quick=1

We have not been querying for the EXT_float_blend explicitly.  However, adding a query for it does not resolve the issue.  (The gl context returns null for the  EXT_float_blend extension.)

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