Function GetParamFallbackValue

Hydrogent/src/HnMaterialNetwork.cpp:298–375

pxr::VtValue GetParamFallbackValue(const pxr::HdMaterialNetwork2& Network,
                                   const pxr::HdMaterialNode2&    Node,
                                   const pxr::TfToken&            ParamName)
{
    // The 'fallback value' will be the value of the material param if nothing
    // is connected or what is connected is mis-configured. For example a
    // missing texture file.

    // Check if there are any connections to the terminal input.
    {
        const auto conn_it = Node.inputConnections.find(ParamName);
        if (conn_it != Node.inputConnections.end())
        {
            if (!conn_it->second.empty())
            {
                const pxr::HdMaterialConnection2& Connection = conn_it->second.front();

                const auto up_it = Network.nodes.find(Connection.upstreamNode);
                if (up_it != Network.nodes.end())
                {
                    const pxr::HdMaterialNode2& UpstreamNode = up_it->second;

                    const pxr::VtValue FallbackValue =
                        GetNodeFallbackValue(UpstreamNode, Connection.upstreamOutputName);
                    if (!FallbackValue.IsEmpty())
                    {
                        return FallbackValue;
                    }
                }
            }
        }
    }

    // If there are no connections, there may be an authored value.
    {
        const auto param_it = Node.parameters.find(ParamName);
        if (param_it != Node.parameters.end())
        {
            return param_it->second;
        }
    }

    // If we had nothing connected, but we do have an Sdr node, we can use the
    // DefaultValue for the input as specified in the Sdr schema.
    // E.g. PreviewSurface is a terminal with an Sdr schema.
    {
        pxr::SdrRegistry& ShaderReg = pxr::SdrRegistry::GetInstance();

        pxr::SdrShaderNodeConstPtr TerminalSdr =
            ShaderReg.GetShaderNodeByIdentifierAndType(Node.nodeTypeId, pxr::HioGlslfxTokens->glslfx);

        if (TerminalSdr)
        {
            if (const pxr::SdrShaderPropertyConstPtr& Input = TerminalSdr->GetShaderInput(ParamName))
            {
                pxr::VtValue Out = Input->GetDefaultValue();
                // If no default value was registered with Sdr for
                // the output, fallback to the type's default.