Attentuation for Directional/Sun Lights when importing Blender files

[amras0000]

_importer = _manager.loadAndInstantiate("BlenderImporter");
_importer->openFile("lights.blend")
Containers::Optional<Trade::LightData> l = _importer->light(0);

Blender 3.0.0 allows for 4 types of light by default: Point, Sun, Spot, and Area. Here are the results when I run the importer on each of these lights:

Loading point.blend ...
Found a light of type Trade::LightData::Type::Point !
Loading spot.blend ...
Found a light of type Trade::LightData::Type::Spot !
Loading area.blend ...
Trade::AssimpImporter::light(): light type 5 is not supported
No light Found !
Loading sun.blend ...
Trade::LightData: attenuation has to be (1, 0, 0) for an ambient or directional light but got Vector(0, 0, 0)
Aborted (core dumped)

Area lights are not supported, and gracefully pass with a warning and a NullOpt. Directional (ie. sun) lights however, note a different attenuation notation and crash before light() exits - meaning the user has no opportunity to fix the attenuation to the expected value.

Test code and blender files are attached.

magnum-blender-directional-light.zip

[pezcode]

Looks like this comment was too optimistic:

magnum-plugins/src/MagnumPlugins/AssimpImporter/AssimpImporter.cpp

Line 895 in 4baaebe

/* For a DIRECTIONAL and AMBIENT light this is (1, 0, 0), which is

That'll need hardcoded attentuation {1, 0, 0} for ambient and directional lights.

Edit: indeed the assimp docs mention that attenuation is "naturally undefined for directional lights".

[mosra]

Oh, fun, new Assimp bugs! :)

We have this tested for COLLADA, where gives us the correct value, and the expectation was that it would have a consistent behavior across various file formats. Such value also makes sense -- the attenuation isn't "undefined" but rather constant, which is what {1, 0, 0} is.

But, in a typical Assimp fashion, it doesn't, and it just does whatever it feels like doing, differently for each file type. Thanks for the repro code, I'll look into this and add a workaround.

[mosra]

Should be fixed with 7936009. If not, please complain :)