GL Backend Doesn't Support Cube Map Arrays

[zicklag]

Description
GLES backend does not appear to support cube map array textures. This is more of a discussion to see how we might be able to support cube arrays if that is possible at all.

Repro steps
I ran into this while trying to run the new Bevy renderer on the GL backend. I don't have a small example, to test unfortunately.

Expected vs observed behavior
Expected that I could create a cube map array, but got an invalid operation error:

Jul 29 19:20:22.748 ERROR submit_graph_commands: wgpu_hal::gles::egl: GLES: [API/Error] ID 1 : GL_INVALID_OPERATION in glFramebufferTexture2D(invalid textarget GL_TEXTURE_CUBE_MAP_ARRAY)    

Extra materials
None

Platform
Ubuntu 20.04 WGPU@master (bbeb30a)

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Edit: A quick check seems to show that cube map arrays are supported in GLES 3.2. Also there is this extension for ES 3.1 EXT_texture_cube_map_array. I'd bet that this is impossible to support in WebGL. 😦

Edit 2: From what I see, it looks like we already have a downlevel flag for this, and I'm actually running GLES 3.2 so it should work. I'll look more into what the problem might be.

[teoxoy]

Closing as this should be resolved.

The only way to run into this at the time was:

• if any attachment was a GL_TEXTURE_CUBE_MAP_ARRAY; this wasn't validated before but now is Update TextureView validation #3410
• copy texture to texture where the src was GL_TEXTURE_CUBE_MAP_ARRAY; which gles: Fix rendering to cubemap faces #2139 fixed