What makes an STL file loaded through vsgXchange visible?

[dov]

While learning vulkanscenegraph, I'm writing my own viewer program based on vsgviewer. I'd like to change the material appearance of an STL mesh loaded into the viewer through vsgXchange. Since an STL file is just pure geometry, I assume that vsgXchange fills in various default properties/nodes on its own. I had a look at the resulting vsgt as output by vsgconv, and tried to find a light/illumination node, but I could not find it. So what makes it visible?

In contrast, if I create through a vsg::Builder, I have figured out that I must add a light on my own to the scene, e.g. by vsg::createHeadlight(). Is there any way of making a model loaded by vsgXchange, behave the same, so that I have to add illumination on my own?

[robertosfield]

STL files are loaded via vsgXchange::assimp, this by uses either the PBR ShaderSet or Phong ShaderSet, both of which fully support lighting and shadows, just like the vsg::Builder generated meshes do.

However, lighting depends upon the dataset having normals, and it could be that assimp isn't creating normals - if there are no normals on the original model then this would be correct. assimp does have support for generating normals. You can enable options like generating normals using vsg::Options class, and there is support for parsing command line args to map to these vsg::Options.

You can list the supported options using vsgconv --features vsgXchange::assimp:

$ vsgconv --features vsgXchange::assimp
vsgXchange::assimp provides support for 70 extensions, and 0 protocols.
    Extensions      Supported ReaderWriter methods
    ----------      ------------------------------
    .3d             read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .3ds            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .3mf            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ac             read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ac3d           read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .acc            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .amf            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ase            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ask            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .assbin         read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .b3d            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .blend          read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .bsp            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .bvh            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .cob            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .csm            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .dae            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .dxf            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .enff           read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .fbx            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .glb            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .gltf           read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .hmp            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ifc            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ifczip         read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .iqm            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .irr            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .irrmesh        read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .lwo            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .lws            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .lxo            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .md2            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .md3            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .md5anim        read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .md5camera      read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .md5mesh        read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .mdc            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .mdl            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .mesh           read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .mesh.xml       read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .mot            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ms3d           read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ndo            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .nff            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .obj            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .off            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ogex           read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .pk3            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ply            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .pmx            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .prj            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .q3o            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .q3s            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .raw            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .scn            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .sib            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .smd            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .step           read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .stl            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .stp            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .ter            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .uc             read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .vta            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .x              read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .x3d            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .x3db           read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .xgl            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .xml            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .zae            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 
    .zgl            read(vsg::Path, ..) read(std::istream, ..) read(uint8_t* ptr, size_t size, ..) 

    vsg::Options::Value      type
    -------------------      ----
    crease_angle             float
    culling                  bool
    discard_empty_nodes      bool
    external_texture_format  vsgXchange::TextureFormat
    external_textures        bool
    generate_sharp_normals   bool
    generate_smooth_normals  bool
    print_assimp             int
    sRGBTextures             bool
    two_sided                bool