Test uploading individual LOD levels to 3D textures from images

[Jimbly]

See:
https://issues.chromium.org/issues/40910322

[CLAassistant]

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[Jimbly]

Notes:

• (expected) Currently fails on Chrome on all platforms when uploading mipmaps of larger (128x128) 3D textures (see linked bug)
• (unsure) The R[GBA]_INTEGER/UNSIGNED_BYTE for TEXTURE_3D (not TEXTURE_2D_ARRAY) tests fail for me (on any browser), where it seems the sampling is wrapping around, or something similar - not sure if this is indicating I have something wrong with my tests, or if this is a GPU or implementation bug

[Jimbly]

Using TEXTURE_MIN/MAX_LOD here works in all tests except for the unsigned integer formats (where it appears to sample from the wrong level). I'm not sure if that means there's something I don't understand, or if I've stumbled upon a bug. I'd be happy to change this code to also test the alternative way to choose which lod levels are sampled from, or to remove this (currently unreachable) branch if desired.

[Jimbly]

Anything required to get this merged or anything I can do to help move the process along?

[kenrussell]

Hi, apologies for dropping this on the floor.

It's been on my plate to study, potentially simplify, and debug this test case for a while. Have pulled this up in my to-do list. The test passes in Firefox and Safari and fails in Chrome, indicating a bug in Chrome's texture upload path.

[Jimbly]

Thanks, good to hear! That is the same results I saw in my testing. Let me know if there's anything I can do to help. Unfortunately the bug doesn't happen unless the textures are over a certain size, and sourced from an IMG element, and targeting an LOD level, so there's probably not a ton that can be simplified (though my unfamiliarity with the testing framework probably left room for improvement, as well as the unknowns I commented on ^_^).