Function GetNodeFallbackValue

Hydrogent/src/HnMaterialNetwork.cpp:248–295

Get the fallback value for material node, first consulting Sdr to find whether the node has an input for the fallback value and then checking whether the output named outputName is known to Sdr and using either the default value specified by the SdrShaderProperty or using a default constructed value of the type specified by SdrShaderProperty.

// the default value specified by the SdrShaderProperty or using a
// default constructed value of the type specified by SdrShaderProperty.
pxr::VtValue GetNodeFallbackValue(const pxr::HdMaterialNode2& Node,
                                  const pxr::TfToken&         OutputName)
{
    pxr::SdrRegistry& ShaderReg = pxr::SdrRegistry::GetInstance();

    // Find the corresponding Sdr node.
    const pxr::SdrShaderNodeConstPtr SdrNode =
        ShaderReg.GetShaderNodeByIdentifierAndType(Node.nodeTypeId, pxr::HioGlslfxTokens->glslfx);
    if (!SdrNode)
    {
        return pxr::VtValue{};
    }


    // HACK: Incorrect usage of GetDefaultInput to
    // determine what the fallback value is.
    // GetDefaultInput is meant to be used for 'disabled'
    // node where the 'default input' becomes the value
    // pass-through in the network. But there is no other
    // mechanism currently to deal with fallback values.
    if (const pxr::SdrShaderPropertyConstPtr& DefaultInput = SdrNode->GetDefaultInput())
    {
        const pxr::TfToken& DefInputName = DefaultInput->GetName();
        auto const&         def_param_it = Node.parameters.find(DefInputName);
        if (def_param_it != Node.parameters.end())
        {
            return def_param_it->second;
        }
    }

    // Sdr supports specifying default values for outputs so if we
    // did not use the GetDefaultInput hack above, we fallback to
    // using this DefaultOutput value.
    if (const pxr::SdrShaderPropertyConstPtr& Output = SdrNode->GetShaderOutput(OutputName))
    {
        const pxr::VtValue Out = Output->GetDefaultValue();
        if (!Out.IsEmpty())
        {
            return Out;
        }

        // If no default value was registered with Sdr for
        // the output, fallback to the type's default.
        return Output->GetTypeAsSdfType().first.GetDefaultValue();
    }

    return pxr::VtValue{};
}


pxr::VtValue GetParamFallbackValue(const pxr::HdMaterialNetwork2& Network,