Material texture layer support for TinyGltfImporter and AssimpImporter

[Squareys]

Hi @mosra !

Here's the accompanying PR for mosra/magnum#438.

TODOs:

• Compile check
• Add configuration value for textures sets
• Testing (A gltf+glb file with a different layer for each, reusing that for assimp, too)
• Advertise support

[mosra]

gltf+glb

Just FYI I don't think you need both, just gltf alone is simple (and you can cut that part out of the material-invalid.gltf where it checks all cases).

For Assimp I'm afraid a glTF won't work (at least not on the ass-old versions on the CI), but copying and modifying one of COLLADA files could be easy enough I hope.

[mosra]

Same as in case of the TinyGltf test -- ideally two variants, testing that the default behavior correctly fails. This also means you need to have three four different materials in order to verify each of the diffuse/specular/ambient/normal failures is done correctly. Instanced tests might (or might not) be helpful.

(What about a specular texture here?)

[Squareys]

I actually solved this before reading your comment... the second ambient should have been specular (copy pasta), and the failure is now also tested, but not separate. Maybe check really quick if the new version satisfies your requirements :)

[codecov-io]

Codecov Report

Merging #83 into master will decrease coverage by 0.24%.
The diff coverage is 68.62%.

@@            Coverage Diff             @@
##           master      #83      +/-   ##
==========================================
- Coverage   93.44%   93.20%   -0.25%     
==========================================
  Files          81       81              
  Lines        5496     5532      +36     
==========================================
+ Hits         5136     5156      +20     
- Misses        360      376      +16     

Impacted Files	Coverage Δ
.../MagnumPlugins/TinyGltfImporter/TinyGltfImporter.h	100.00% <ø> (ø)
...rc/MagnumPlugins/AssimpImporter/AssimpImporter.cpp	87.00% <57.89%> (-2.56%)	⬇️
...agnumPlugins/TinyGltfImporter/TinyGltfImporter.cpp	97.44% <100.00%> (+0.01%)	⬆️

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[Squareys]

@mosra FYI, this is ready and I'm currently waiting for feedback on this :)

[mosra]

Thx!