IECoreUSD::ShaderAlgo : Round-trip ColorSpace data on shader parameters.

Author: Alex Fuller

Changes

@@ -1,7 +1,10 @@
 10.5.x.x (relative to 10.5.13.0)
 ========
 
+Features
+--------
 
+- IECoreUSD::ShaderAlgo : Round-trip ColorSpace data that is stored on USD Attributes by storing an additional parameter with the `_colorspace` suffix.
 
 10.5.13.0 (relative to 10.5.12.0)
 =========

contrib/IECoreUSD/src/IECoreUSD/ShaderAlgo.cpp

@@ -244,6 +244,16 @@ IECore::InternedString readShaderNetworkWalk( const pxr::SdfPath &anchorPath, co
 		if( IECore::DataPtr d = IECoreUSD::DataAlgo::fromUSD( pxr::UsdAttribute( valueAttribute ) ) )
 		{
 			parameters[fromUSDParameterName( i.GetBaseName() )] = d;
+			// If there's colorspace data on the parameter, we can store this as
+			// `<name>_colorspace`, this is how MaterialX stores colorspace on
+			// generated OSL nodes so we match here the same behaviour.
+			if( pxr::UsdAttribute( valueAttribute ).HasColorSpace() )
+			{
+				const IECore::InternedString colorSpace( pxr::UsdAttribute( valueAttribute ).GetColorSpace().GetString() );
+				const IECore::InternedString paramName(
+					( boost::format( "%s_colorspace" ) % fromUSDParameterName( i.GetBaseName() ).string() ).str() );
+				parameters[paramName] = new IECore::InternedStringData( colorSpace );
+			}
 		}
 	}
 
@@ -334,6 +344,13 @@ void writeShaderParameterValues( const IECoreScene::Shader *shader, pxr::UsdShad
 			continue;
 		}
 
+		// Skip colorspace parameters, these will be set using SetColorSpace() on the
+		// USD attribue that it corresponds to.
+		if( boost::ends_with( p.first.string(), "_colorspace" ) )
+		{
+			continue;
+		}
+
 		const pxr::TfToken usdParameterName = toUSDParameterName( p.first );
 		pxr::UsdShadeInput input = usdShader.GetInput( usdParameterName );
 		if( !input )
@@ -364,6 +381,17 @@ void writeShaderParameterValues( const IECoreScene::Shader *shader, pxr::UsdShad
 			}
 		}
 		input.Set( IECoreUSD::DataAlgo::toUSD( p.second.get() ) );
+
+		// Make sure to set any colorspace parameters onto the attribute
+		// if any exist.
+		auto it = shader->parameters().find( ( boost::format( "%s_colorspace" ) % p.first.string() ).str() );
+		if( it != shader->parameters().end() )
+		{
+			if( auto *s = IECore::runTimeCast<IECore::InternedStringData>( it->second.get() ) )
+			{
+				pxr::UsdAttribute( input ).SetColorSpace( pxr::TfToken( s->readable().string() ) );
+			}
+		}
 	}
 
 	if( shader->blindData()->readable().size() )

contrib/IECoreUSD/test/IECoreUSD/USDSceneTest.py

@@ -2877,6 +2877,7 @@ def testShaders( self ) :
 
 		texture = IECoreScene.Shader( "texture", "ai:shader" )
 		texture.parameters["filename"] = IECore.StringData( "sometexture.tx" )
+		texture.parameters["filename_colorspace"] = IECore.InternedStringData( "ACEScg" )
 
 		oneShaderNetwork = IECoreScene.ShaderNetwork()
 		oneShaderNetwork.addShader( "foo", surface )
@@ -3064,6 +3065,8 @@ def testShaders( self ) :
 		textureUsd = pxr.UsdShade.Shader( add1Source[0].GetPrim() )
 		self.assertEqual( textureUsd.GetShaderId(), "arnold:texture" )
 		self.assertEqual( textureUsd.GetInput( "filename" ).Get(), "sometexture.tx" )
+		self.assertEqual( add1Source[0].GetPrim().GetAttribute( "inputs:filename" ).GetColorSpace(), "ACEScg" )
+		self.assertEqual( add1Source[0].GetPrim().HasAttribute( "inputs:filename_colorspace", False )
 
 
 		# Read via SceneInterface, and check that we've round-tripped successfully.
@@ -3340,6 +3343,15 @@ def testTextureParameters( self ) :
 			os.path.normcase( os.path.normpath( network.getShader( "udimTexture" ).parameters["file"].value ) ),
 			os.path.normcase( os.path.normpath( "/full/path/to/myTexture.<UDIM>.tx" ) )
 		)
+		self.assertEqual(
+			network.getShader( "relativeTexture" ).parameters["file_colorspace"].value, "ACEScg"
+		)
+		self.assertEqual(
+			network.getShader( "relativeUDIMTexture" ).parameters["file_colorspace"].value, "lin_rec709_scene"
+		)
+		self.assertEqual(
+			network.getShader( "udimTexture" ).parameters["file_colorspace"].value, "srgb_rec709_scene"
+		)
 
 	def testExposedShaderInput( self ) :
 

contrib/IECoreUSD/test/IECoreUSD/data/textureParameters.usda

@@ -29,22 +29,28 @@ def "model"
 			def Shader "relativeTexture"
 			{
 				uniform token info:id = "UsdUVTexture"
-				asset inputs:file = @../myTexture.tx@
+				asset inputs:file = @../myTexture.tx@ (
+					colorSpace = "ACEScg"
+				)
 				vector3f outputs:rgb
 			}
 
 			def Shader "relativeUDIMTexture"
 			{
 				uniform token info:id = "UsdUVTexture"
-				asset inputs:file = @../myTexture.<UDIM>.tx@
+				asset inputs:file = @../myTexture.<UDIM>.tx@ (
+					colorSpace = "lin_rec709_scene"
+				)
 				vector3f outputs:rgb
 
 			}
 
 			def Shader "udimTexture"
 			{
 				uniform token info:id = "UsdUVTexture"
-				asset inputs:file = @/full/path/to/myTexture.<UDIM>.tx@
+				asset inputs:file = @/full/path/to/myTexture.<UDIM>.tx@ (
+					colorSpace = "srgb_rec709_scene"
+				)
 				float outputs:r
 			}
 		}