IECoreUSD::ShaderAlgo : Handle connections to exposed material inputs

Author: johnhaddon

contrib/IECoreUSD/src/IECoreUSD/ShaderAlgo.cpp

@@ -88,14 +88,25 @@ IECore::InternedString readShaderNetworkWalk( const pxr::SdfPath &anchorPath, co
 		pxr::TfToken usdSourceName;
 		pxr::UsdShadeAttributeType usdSourceType;
 
-		if( IECore::DataPtr d = IECoreUSD::DataAlgo::fromUSD( pxr::UsdAttribute( i ) ) )
+		pxr::UsdAttribute valueAttribute = i;
+		if( i.GetConnectedSource( &usdSource, &usdSourceName, &usdSourceType ) )
 		{
-			parameters[ i.GetBaseName().GetString() ] = d;
+			if( !usdSource.IsContainer() )
+			{
+				connections.push_back( { i.GetBaseName().GetString(), usdSource, usdSourceName.GetString() } );
+			}
+			else
+			{
+				// Connected to an exposed input on the material container. We don't
+				// have an equivalent in IECoreScene::ShaderNetwork yet, so just take
+				// the parameter value from the exposed input.
+				valueAttribute = usdSource.GetInput( usdSourceName );
+			}
 		}
 
-		if( i.GetConnectedSource( &usdSource, &usdSourceName, &usdSourceType ) )
+		if( IECore::DataPtr d = IECoreUSD::DataAlgo::fromUSD( pxr::UsdAttribute( valueAttribute ) ) )
 		{
-			connections.push_back( { i.GetBaseName().GetString(), usdSource, usdSourceName.GetString() } );
+			parameters[ i.GetBaseName().GetString() ] = d;
 		}
 	}
 

contrib/IECoreUSD/test/IECoreUSD/USDSceneTest.py

@@ -2952,5 +2952,20 @@ def testAssetAttributes( self ) :
 			IECore.StringData( os.path.join( os.path.dirname( __file__ ), "data", "cube.usda" ) )
 		)
 
+	def testExposedShaderInput( self ) :
+
+		root = IECoreScene.SceneInterface.create(
+			os.path.join( os.path.dirname( __file__ ), "data", "exposedShaderInput.usda" ),
+			IECore.IndexedIO.OpenMode.Read
+		)
+		sphere = root.child( "model" ).child( "sphere" )
+
+		self.assertEqual( sphere.attributeNames(), [ "surface" ] )
+		network = sphere.readAttribute( "surface", 0 )
+
+		self.assertEqual( network.size(), 1 )
+		self.assertEqual( network.getOutput(), "surface" )
+		self.assertEqual( network.getShader( "surface" ).parameters["diffuse_roughness"].value, 0.75 )
+
 if __name__ == "__main__":
 	unittest.main()

contrib/IECoreUSD/test/IECoreUSD/data/exposedShaderInput.usda

@@ -0,0 +1,30 @@
+#usda 1.0
+
+def "model"
+{
+
+	def Sphere "sphere"
+	{
+		rel material:binding = </model/materials/material1>
+	}
+
+	def Scope "materials"
+	{
+
+		def Material "material1"
+		{
+
+			float inputs:exposedRoughness = 0.75
+			token outputs:surface.connect = </model/materials/material1/surface.outputs:DEFAULT_OUTPUT>
+
+			def Shader "surface"
+			{
+				uniform token info:id = "arnold:standard_surface"
+				float inputs:diffuse_roughness.connect = </model/materials/material1.inputs:exposedRoughness>
+				token outputs:DEFAULT_OUTPUT
+			}
+		}
+
+	}
+
+}