3Delight ShaderNetworkAlgo : Initial support for translating colorspace

`{param}_meta_colorspace` is a 3Delight convention for declaring the input colorspace of the texture at `{param}`.

From the 3Delight docs:

In NSI `textureName.meta.colorspace` indicates the color space for the texture designated by `textureName`. Any available OCIO color space can be used. The following presets are recognised: linear, rec.709, sRGB.

python/IECoreDelightTest/ShaderNetworkAlgoTest.py

@@ -343,6 +343,7 @@ def testConvertSimpleUSDUVTexture( self ) :
 			self.assertEqual( texture.parameters["file"].value, "test.png" )
 			self.assertEqual( texture.parameters["wrapS"].value, "useMetadata" )
 			self.assertEqual( texture.parameters["wrapT"].value, "repeat" )
+			self.assertEqual( texture.parameters["file_meta_colorspace"].value, "auto" )
 
 	def testConvertSimpleUSDNormalTexture( self ) :
 
@@ -391,6 +392,7 @@ def testConvertSimpleUSDNormalTexture( self ) :
 			self.assertEqual( texture.parameters["file"].value, "test.png" )
 			self.assertEqual( texture.parameters["wrapS"].value, "useMetadata" )
 			self.assertEqual( texture.parameters["wrapT"].value, "repeat" )
+			self.assertEqual( texture.parameters["file_meta_colorspace"].value, "raw" )
 
 	def testConvertTransformedUSDUVTexture( self ) :
 
@@ -440,6 +442,7 @@ def testConvertTransformedUSDUVTexture( self ) :
 		self.assertEqual( texture.parameters["file"].value, "test.png" )
 		self.assertEqual( texture.parameters["wrapS"].value, "repeat" )
 		self.assertEqual( texture.parameters["wrapT"].value, "repeat" )
+		self.assertEqual( texture.parameters["file_meta_colorspace"].value, "auto" )
 
 		uvReader = convertedNetwork.getShader( "uvReader" )
 		self.assertEqual( uvReader.name, "dlPrimitiveAttribute" )

shaders/__usd/__usdUVTexture.osl

@@ -51,6 +51,7 @@ string convertWrap( string wrap )
 shader __usdUVTexture
 (
 	string file = "",
+	string file_meta_colorspace = "",
 	float uvCoord[2] = {0, 0},
 	string wrapS = "default",
 	string wrapT = "default",

src/IECoreDelight/ShaderNetworkAlgo.cpp

@@ -426,6 +426,7 @@ const InternedString g_exposureParameter( "exposure" );
 const InternedString g_fallbackParameter( "fallback" );
 const InternedString g_fallbackValueParameter( "fallback_value" );
 const InternedString g_fileParameter( "file" );
+const InternedString g_fileMetaColorSpaceParameter( "file_meta_colorspace" );
 const InternedString g_gParameter( "g" );
 const InternedString g_heightParameter( "height" );
 const InternedString g_inParameter( "in" );
@@ -462,6 +463,7 @@ const InternedString g_roughnessParameter( "roughness" );
 const InternedString g_scaleParameter( "scale" );
 const InternedString g_shapingConeAngleParameter( "shaping:cone:angle" );
 const InternedString g_shapingConeSoftnessParameter( "shaping:cone:softness" );
+const InternedString g_sourceColorSpaceParameter( "sourceColorSpace" );
 const InternedString g_specularParameter( "specular" );
 const InternedString g_specularColorParameter( "specularColor" );
 const InternedString g_specularColorDelightParameter( "specular_color" );
@@ -750,6 +752,7 @@ void convertUSDUVTextures( ShaderNetwork *network )
 
 		ShaderPtr imageShader = new Shader( "__usd/__usdUVTexture", "osl:shader" );
 		transferUSDParameter( network, handle, shader.get(), g_fileParameter, imageShader.get(), g_fileParameter, std::string() );
+		transferUSDParameter( network, handle, shader.get(), g_sourceColorSpaceParameter, imageShader.get(), g_fileMetaColorSpaceParameter, std::string( "auto" ) );
 
 		transferUSDParameter( network, handle, shader.get(), g_fallbackParameter, imageShader.get(), g_fallbackParameter, Color4f( 0, 0, 0, 1 ) );
 		transferUSDParameter( network, handle, shader.get(), g_scaleParameter, imageShader.get(), g_scaleParameter, Color4f( 1 ) );