USD ShaderAlgo : Fix writing of SdfAssetPath and TfToken inputs

These cases occur when writing to UsdLuxLight types where the inputs already exist, and don't need to be defined by us.

Author: johnhaddon

contrib/IECoreUSD/src/IECoreUSD/ShaderAlgo.cpp

@@ -255,10 +255,29 @@ void writeShaderParameterValues( const IECoreScene::Shader *shader, pxr::UsdShad
 {
 	for( const auto &p : shader->parametersData()->readable() )
 	{
-		pxr::UsdShadeInput input = usdShader.CreateInput(
-			toUSDParameterName( p.first ),
-			IECoreUSD::DataAlgo::valueTypeName( p.second.get() )
-		);
+		const pxr::TfToken usdParameterName = toUSDParameterName( p.first );
+		pxr::UsdShadeInput input = usdShader.GetInput( usdParameterName );
+		if( !input )
+		{
+			input = usdShader.CreateInput(
+				toUSDParameterName( p.first ),
+				IECoreUSD::DataAlgo::valueTypeName( p.second.get() )
+			);
+		}
+		if( auto *s = IECore::runTimeCast<IECore::StringData>( p.second.get() ) )
+		{
+			// USD has several "stringy" types - convert if necessary.
+			if( input.GetTypeName() == pxr::SdfValueTypeNames->Token )
+			{
+				input.Set( pxr::TfToken( s->readable() ) );
+				continue;
+			}
+			else if( input.GetTypeName().GetType().IsA<pxr::SdfAssetPath>() )
+			{
+				input.Set( pxr::SdfAssetPath( s->readable() ) );
+				continue;
+			}
+		}
 		input.Set( IECoreUSD::DataAlgo::toUSD( p.second.get() ) );
 	}
 

contrib/IECoreUSD/test/IECoreUSD/USDSceneTest.py

@@ -3444,6 +3444,32 @@ def testWriteLightWithInputNetwork( self ) :
 
 		self.assertEqual( light.GetPrim().GetChildren(), [ source.GetPrim() ] )
 
+	def testWriteDomeLightFile( self ) :
+
+		# Write to USD
+
+		fileName = os.path.join( self.temporaryDirectory(), "pointInstancePrimvars.usda" )
+		scene = IECoreScene.SceneInterface.create( fileName, IECore.IndexedIO.OpenMode.Write )
+
+		lightNetwork = IECoreScene.ShaderNetwork(
+			shaders = {
+				"output" : IECoreScene.Shader( "DomeLight", "light", { "texture:file" : "test.exr", "texture:format" : "latlong" } ),
+			},
+			output = "output",
+		)
+
+		light = scene.createChild( "light" )
+		light.writeAttribute( "light", lightNetwork, 0 )
+
+		del light, scene
+
+		# Verify via USD API
+
+		stage = pxr.Usd.Stage.Open( fileName )
+		light = pxr.UsdLux.DomeLight( stage.GetPrimAtPath( "/light" ) )
+		self.assertEqual( light.GetTextureFileAttr().Get(), "test.exr" )
+		self.assertEqual( light.GetTextureFormatAttr().Get(), "latlong" )
+
 	def testPointInstancerPrimvars( self ) :
 
 		# Use the USD API to author a point instancer with primvars on it.