Data is rendered incorrectly on iOS 14

[philippotto]

Context

When viewing a dataset via browserstack on iPad Air 4 (iOS 14), data is often rendered incorrectly. The console outputs:

maxTextureImageUnits 16
vendors~main.js?nocache=2f751a7…:249 maximumLayerCountToRender 8
vendors~main.js?nocache=2f751a7…:249 Supporting 4096 buckets
vendors~main.js?nocache=2f751a7…:249 THREE.WebGLRenderer: OES_texture_float_linear extension not supported.
vendors~main.js?nocache=2f751a7…:249 Requested api version: 3 which is the latest version.

For iOS 13, the same bug does not occur and the output is:

vendors~main.js?nocache=2f751a7…:249 maxTextureImageUnits 8
vendors~main.js?nocache=2f751a7…:249 maximumLayerCountToRender 2
vendors~main.js?nocache=2f751a7…:249 Supporting 2048 buckets
vendors~main.js?nocache=2f751a7…:249 Requested api version: 3 which is the latest version.
vendors~main.js?nocache=2f751a7…:249 THREE.WebGLProgram: gl.getProgramInfoLog() WARNING: Output of vertex shader 'vUv' not read by fragment shader
WARNING: Output of vertex shader 'modelCoord' not read by fragment shader

I'm not really sure whether the OES_texture_float_linear bit is really the culprit, since my research showed that earlier iOS versions didn't support that bit either (but didn't say so).

Expected Behavior

Data should be rendered correctly.

Current Behavior

Steps to Reproduce the bug

• Cannot reproduce the bug anymore / needs deeper investigation.

1. open wk on iPad 4 with iOS 14
2. open a dataset
3. zoom in to mag 1
4. move a bit

Your Environment for bug

• Browser name and version: e.g. Chrome 39
• Operating System and version: e.g. Windows 10
• Version of WebKnossos (Release or Commit):
• Specific to long-running jobs (set jobsEnabled=true in application.conf)
• Specific to webKnossos.org (set isDemoInstance=true in application.conf)

[philippotto]

I'm not really sure whether the OES_texture_float_linear bit is really the culprit, since my research showed that earlier iOS versions didn't support that bit either (but didn't say so).

Since we always use THREE.NearestFilter for textures, this shouldn't explain the bug.

Further insights: I can only reproduce this issue for non-uint8 (namely, uint16) layers (regardless of color or segmentation). Unfortunately, I couldn't find any workaround or more details about what's exactly going wrong on iOS 14.

[hotzenklotz]

Voting to close this issue, since iOS14 is outdated (iOS16 was just released) and we update wK to WebGL2 + ThreeJS updates.