How to read illum value from mtl file using Assimp library?
According to the source (https://github.com/assimp/assimp/blob/b7df376836e36c4b6998ce95d97626e30f61c2f0/code/AssetLib/Obj/ObjFileImporter.cpp#L594) only illum values of 0, 1, 2 are supported:
    // convert illumination model
    int sm = 0;
    switch (pCurrentMaterial-&gt;illumination_model) {
    case 0:
        sm = aiShadingMode_NoShading;
        break;
    case 1:
        sm = aiShadingMode_Gouraud;
        break;
    case 2:
        sm = aiShadingMode_Phong;
        break;
    default:
        sm = aiShadingMode_Gouraud;
        ASSIMP_LOG_ERROR(&quot;OBJ: unexpected illumination model (0-2 recognized)&quot;);
    }