Merge pull request #1233 from johnhaddon/usdVaryingLengthArrays

USDScene : Support Houdini's varying-length-array-per-vertex primvars

Author: johnhaddon

.github/workflows/main.yml

@@ -90,7 +90,7 @@ jobs:
             buildType: RELWITHDEBINFO
             options: .github/workflows/main/options.windows
             dependenciesURL: https://github.com/hypothetical-inc/gafferDependencies/releases/download/3.1.1/gafferDependencies-3.1.1-Python3-windows.zip
-            tests: testCore testCorePython testScene testImage testAlembic testVDB
+            tests: testCore testCorePython testScene testImage testAlembic testUSD testVDB
             publish: false
 
     runs-on: ${{ matrix.os }}

contrib/IECoreUSD/include/IECoreUSD/AttributeAlgo.h

@@ -43,6 +43,7 @@ IECORE_PUSH_DEFAULT_VISIBILITY
 #include "pxr/base/tf/token.h"
 #include "pxr/usd/usd/attribute.h"
 #include "pxr/usd/usd/prim.h"
+#include "pxr/usd/usdGeom/primvar.h"
 IECORE_POP_DEFAULT_VISIBILITY
 
 // AttributeAlgo is suite of utilities for loading/writing Cortex/USD Attributes.
@@ -53,8 +54,6 @@ namespace IECoreUSD
 namespace AttributeAlgo
 {
 
-
-
 // Find a UsdAttribute under the given prim which matches the given cortex name.  This UsdAttribute
 // could be either a constant primvar or a custom attribute with an appropriate name.  If no matching
 // UsdAttribute is found, returns an invalid UsdAttribute
@@ -66,6 +65,10 @@ IECOREUSD_API pxr::UsdAttribute findUSDAttribute( const pxr::UsdPrim &prim, std:
 // or a non-custom primvar, then an empty string is returned.
 IECOREUSD_API IECore::InternedString cortexAttributeName( const pxr::UsdAttribute &attribute );
 
+// Returns true if the primvar should be loaded as a Cortex attribute rather than
+// a PrimitiveVariable.
+IECOREUSD_API bool isCortexAttribute( const pxr::UsdGeomPrimvar &primVar );
+
 struct Name
 {
 	pxr::TfToken name;

contrib/IECoreUSD/src/IECoreUSD/AttributeAlgo.cpp

@@ -45,42 +45,56 @@ IECORE_POP_DEFAULT_VISIBILITY
 using namespace IECoreUSD;
 using namespace pxr;
 
-
 namespace
 {
+
 static const pxr::TfToken g_cortexPrimitiveVariableMetadataToken( "cortex_isConstantPrimitiveVariable" );
 static const pxr::TfToken g_cortexPrimitiveVariableMetadataTokenDeprecated( "IECOREUSD_CONSTANT_PRIMITIVE_VARIABLE" );
 static const std::string g_primVarPrefix = "primvars:";
 static const std::string g_primVarUserPrefix = "primvars:user:";
 static const std::string g_renderPrefix = "render:";
 static const std::string g_userPrefix = "user:";
 
-// Cortex Attribute in USD are converted to constant primvar because they behave similarly ( hierarchy inheritance and availability for shading )
-// so we ignore non constant primvar as well as constant primvar that are "tagged" with a special metadata `IECOREUSD_CONSTANT_PRIMITIVE_VARIABLE`
-bool isCortexAttribute( const pxr::UsdGeomPrimvar &primVar )
+}
+
+bool IECoreUSD::AttributeAlgo::isCortexAttribute( const pxr::UsdGeomPrimvar &primVar )
 {
-	if( primVar.GetInterpolation() == pxr::UsdGeomTokens->constant )
+	if( primVar.GetInterpolation() != pxr::UsdGeomTokens->constant )
 	{
-		// skip any non const prim vars or with metadata for Cortex const Primitive Variable
-		pxr::VtValue metadataValue;
-		if( primVar.GetAttr().GetMetadata( AttributeAlgo::cortexPrimitiveVariableMetadataToken(), &metadataValue ) )
-		{
-			return !metadataValue.Get<bool>();
-		}
-		else if( primVar.GetAttr().GetMetadata( AttributeAlgo::cortexPrimitiveVariableMetadataTokenDeprecated(), &metadataValue ) )
-		{
-			return !metadataValue.Get<bool>();
-		}
-		// constant prim var without the metadata then it's a Cortex attribute
-		else
+		return false;
+	}
+
+	// We have a constant primvar. Check the metadata to see if it has been
+	// tagged as a true primvar and not an attribute. If the metadata exists,
+	// that is the final word on the matter.
+
+	pxr::VtValue metadataValue;
+	if( primVar.GetAttr().GetMetadata( AttributeAlgo::cortexPrimitiveVariableMetadataToken(), &metadataValue ) )
+	{
+		return !metadataValue.Get<bool>();
+	}
+	else if( primVar.GetAttr().GetMetadata( AttributeAlgo::cortexPrimitiveVariableMetadataTokenDeprecated(), &metadataValue ) )
+	{
+		return !metadataValue.Get<bool>();
+	}
+
+	// Check for companion `<name>:lengths` primvar. This is a convention
+	// Houdini uses to store varying-length-array primvars per-vertex or
+	// per-face. We want to load the two primvars side by side as primitive
+	// variables.
+
+	const TfToken lengthsName( primVar.GetName().GetString() + ":lengths" );
+	if( auto lengthsPrimVar = UsdGeomPrimvarsAPI( primVar.GetAttr().GetPrim() ).GetPrimvar( lengthsName ) )
+	{
+		if( lengthsPrimVar.GetInterpolation() != pxr::UsdGeomTokens->constant )
 		{
-			return true;
+			return false;
 		}
 	}
 
-	return false;
-}
+	// Everything else should be loaded as a Cortex attribute.
 
+	return true;
 }
 
 pxr::TfToken IECoreUSD::AttributeAlgo::cortexPrimitiveVariableMetadataToken()
@@ -228,3 +242,4 @@ IECore::InternedString IECoreUSD::AttributeAlgo::cortexAttributeName( const pxr:
 	}
 	return IECore::InternedString();
 }
+

contrib/IECoreUSD/src/IECoreUSD/PrimitiveAlgo.cpp

@@ -439,28 +439,9 @@ void IECoreUSD::PrimitiveAlgo::readPrimitiveVariables( const pxr::UsdGeomPrimvar
 			continue;
 		}
 
-		if ( primVar.GetInterpolation() == pxr::UsdGeomTokens->constant )
+		if( AttributeAlgo::isCortexAttribute( primVar ) )
 		{
-			pxr::VtValue metadataValue;
-			if ( primVar.GetAttr().GetMetadata( AttributeAlgo::cortexPrimitiveVariableMetadataToken(), &metadataValue ) )
-			{
-				if ( !metadataValue.Get<bool>() )
-				{
-					continue;
-				}
-			}
-			else if ( primVar.GetAttr().GetMetadata( AttributeAlgo::cortexPrimitiveVariableMetadataTokenDeprecated(), &metadataValue ) )
-			{
-				if ( !metadataValue.Get<bool>() )
-				{
-					continue;
-				}
-			}
-			// constant prim var without the metadata then it's a Cortex Attribute so we skip it as PrimitiveVariable.
-			else
-			{
-				continue;
-			}
+			continue;
 		}
 
 		bool constantAcceptsArray = true;

contrib/IECoreUSD/test/IECoreUSD/USDSceneTest.py

@@ -2900,5 +2900,36 @@ def testShadersAcrossDifferentScopes( self ):
 			) ]
 		)
 
+	def testHoudiniVaryingLengthArrayPrimVar( self ) :
+
+		root = IECoreScene.SceneInterface.create(
+			os.path.join( os.path.dirname( __file__ ), "data", "houdiniVaryingLengthArrayPrimVar.usda" ),
+			IECore.IndexedIO.OpenMode.Read
+		)
+
+		points = root.child( "plane" )
+		self.assertEqual( points.attributeNames(), [] )
+		self.assertFalse( points.hasAttribute( "varyingLengthArray" ) )
+
+		primitive = points.readObject( 1.0 )
+		self.assertEqual(
+			set( primitive.keys() ),
+			{ "P", "varyingLengthArray", "varyingLengthArray:lengths" }
+		)
+		self.assertEqual(
+			primitive["varyingLengthArray"],
+			IECoreScene.PrimitiveVariable(
+				IECoreScene.PrimitiveVariable.Interpolation.Constant,
+				IECore.FloatVectorData( [ 1, 1, 1, 2, 3, 3, 3, 3, 4 ] )
+			)
+		)
+		self.assertEqual(
+			primitive["varyingLengthArray:lengths"],
+			IECoreScene.PrimitiveVariable(
+				IECoreScene.PrimitiveVariable.Interpolation.Vertex,
+				IECore.IntVectorData( [ 3, 1, 4, 1 ] )
+			)
+		)
+
 if __name__ == "__main__":
 	unittest.main()

contrib/IECoreUSD/test/IECoreUSD/data/houdiniVaryingLengthArrayPrimVar.usda

@@ -0,0 +1,22 @@
+#usda 1.0
+
+def Points "plane"
+{
+    point3f[] points = [(-0.5, -0.5, 0), (0.5, -0.5, 0), (-0.5, 0.5, 0), (0.5, 0.5, 0)]
+
+	# USD doesn't allow array primvars with varying-length per vertex.
+	# Houdini works around this by writing two primvars :
+	#
+	#	- A constant one with all the arrays concatenated together
+	#	- A vertex one with the lengths of the array per vertex
+
+	float[] primvars:varyingLengthArray = [ 1, 1, 1, 2, 3, 3, 3, 3, 4 ] (
+		interpolation = "constant"
+	)
+
+	int[] primvars:varyingLengthArray:lengths = [ 3, 1, 4, 1 ] (
+		interpolation = "vertex"
+	)
+
+}
+