Stage open callback or similar

Community USD
1

Hi

I’m quite new with usd and I’m learning the sdk with c++.

Let’s say I have my Gprim like USDPluginExamples/src/usdTri at main · wetadigital/USDPluginExamples · GitHub
In my mind ( I expected at least ) there was a mechanism a callback system or an instancing system during the loading of a stage that automatically build the types based on plugin loaded. In few words: during the loading if a usd triangle is loaded let’s instanciate UsdTriTriangle with the primitive.
For sure I’m wrong so if I need to do stuff with my gprim during the loading the only way is?

UsdStageRefPtr stage = UsdStage::Open(__path__);
    for (UsdPrim prim : stage->TraverseAll()) 
    {
        if (prim.IsA<UsdTriTriangle>()) 
        {
           UsdTriTriangle tri(prim);
           // do your stuff based prim attirbutes
        }
    }

Thanks

2

Hi @gennz , When Opened, a UsdStage will contain a complete “type definition” for all primTypes defined in plugins. However, C++ schema objects for USD prim types are entirely optional (you can search on “codeless schemas”). Further, given that those schema objects may not capture a prim’s complete definition (e.g. because it may have many applied schemas, as well), there is no single C++ schema object that could be pre-manufactured that would satisfy the needs of all consumers.

So we make a clean break between the generic data containers that populate the stage (UsdPrim) which contain the type information for the full prim definition – but do not instantiate any objects based on it – and code-based schema objects provided by schema plugins. This way:

  • A UsdStage remains lighter and simpler
  • Each client gets to decide and instantiate only the schema objects required for its needs

Does that make sense?

3

Yes I understood, Thanks