USDScene : Load bounds from UsdGeomModelAPI extents hints

This can provide significant performance improvements where the ModelAPI has been used to provide cached extents. This knocks around 30% off the time taken to open the file and compute the root bound of the ALab in Gaffer. If USD composition time is omitted so only the bound computation is measured in isolation, a full 95% is knocked off the time. In the case of the ALab, the new root bound is also far more reasonable for some reason - I suspect the model extents are masking a bad authored extent on a leaf object elsewhere in the scene.

This has the potential to be surprising for any folks who have authored inaccurate model extents in the past, so I've made it possible to turn off the behaviour using an environment variable. I'd like to default things on in Cortex itself, but we can debate the appropriate default for Gaffer when we next update the Cortex version.

Author: johnhaddon

Changes

@@ -1,7 +1,10 @@
 10.5.x.x (relative to 10.5.8.0)
 ========
 
+Improvements
+------------
 
+- USDScene : `hasBound()` and `readBound()` now use `UsdGeomModelAPI` extents hints if they are available. This behaviour can be disabled by setting the `IECOREUSD_USE_MODELAPI_BOUNDS` environment variable to a value of `0`.
 
 10.5.8.0 (relative to 10.5.7.1)
 ========

contrib/IECoreUSD/src/IECoreUSD/USDScene.cpp

@@ -58,6 +58,7 @@ IECORE_PUSH_DEFAULT_VISIBILITY
 #include "pxr/usd/usdGeom/camera.h"
 #include "pxr/usd/usdGeom/gprim.h"
 #include "pxr/usd/usdGeom/metrics.h"
+#include "pxr/usd/usdGeom/modelAPI.h"
 #include "pxr/usd/usdGeom/pointInstancer.h"
 #include "pxr/usd/usdGeom/primvar.h"
 #include "pxr/usd/usdGeom/primvarsAPI.h"
@@ -528,6 +529,33 @@ Imath::M44d localTransform( const pxr::UsdPrim &prim, pxr::UsdTimeCode time )
 	return result;
 }
 
+static const bool g_useModelAPIBounds = []() -> bool {
+	const char *c = getenv( "IECOREUSD_USE_MODELAPI_BOUNDS" );
+	if( !c )
+	{
+		return true;
+	}
+	return strcmp( c, "0" );
+}();
+
+pxr::UsdAttribute boundAttribute( const pxr::UsdPrim &prim )
+{
+	if( auto boundable = pxr::UsdGeomBoundable( prim ) )
+	{
+		return boundable.GetExtentAttr();
+	}
+
+	if( g_useModelAPIBounds )
+	{
+		if( auto modelAPI = pxr::UsdGeomModelAPI( prim ) )
+		{
+			return modelAPI.GetExtentsHintAttr();
+		}
+	}
+
+	return pxr::UsdAttribute();
+}
+
 // Used to assign a unique hash to each USD file. Using a global counter rather than the file name
 // means that we treat the same file as separate if it is closed and reopened. This means it's not
 // a problem if USD changes things when a file is reopened. USD appears to not in general guarantee
@@ -820,30 +848,32 @@ std::string USDScene::fileName() const
 
 Imath::Box3d USDScene::readBound( double time ) const
 {
-	pxr::UsdGeomBoundable boundable = pxr::UsdGeomBoundable( m_location->prim );
-	if( !boundable )
-	{
-		return Imath::Box3d();
-	}
-
-	pxr::UsdAttribute attr = boundable.GetExtentAttr();
+	pxr::UsdAttribute attr = boundAttribute( m_location->prim );
 	if( !attr.IsValid() )
 	{
 		return Imath::Box3d();
 	}
 
 	pxr::VtArray<pxr::GfVec3f> extents;
-	attr.Get<pxr::VtArray<pxr::GfVec3f> >( &extents, m_root->getTime( time ) );
+	attr.Get( &extents, m_root->getTime( time ) );
 
-	if( extents.size() == 2 )
+	// When coming from UsdGeomModelAPI, `extents` may contain several bounds,
+	// on a per-purpose basis. Take the union, since the SceneInterface API only
+	// has a single bound per location.
+	Imath::Box3d result;
+	for( size_t i = 0; i + 1 < extents.size(); i += 2 )
 	{
-		return Imath::Box3d(
-			DataAlgo::fromUSD( extents[0] ),
-			DataAlgo::fromUSD( extents[1] )
+		const Imath::Box3d b(
+			DataAlgo::fromUSD( extents[i] ),
+			DataAlgo::fromUSD( extents[i+1] )
 		);
+		if( !b.isEmpty() )
+		{
+			result.extendBy( b );
+		}
 	}
 
-	return Imath::Box3d();
+	return result;
 }
 
 ConstDataPtr USDScene::readTransform( double time ) const
@@ -873,14 +903,7 @@ void USDScene::path( SceneInterface::Path &p ) const
 
 bool USDScene::hasBound() const
 {
-	pxr::UsdGeomBoundable boundable = pxr::UsdGeomBoundable( m_location->prim );
-	pxr::UsdAttribute attr;
-
-	if( boundable )
-	{
-		attr = boundable.GetExtentAttr();
-	}
-
+	pxr::UsdAttribute attr = boundAttribute( m_location->prim );
 	return attr.IsValid();
 }
 

contrib/IECoreUSD/test/IECoreUSD/USDSceneTest.py

@@ -4211,5 +4211,51 @@ def testTreatLightAsPointOrLine( self ) :
 		self.assertEqual( root.child( "sphereLight" ).readAttribute( "light", 0 ), sphereLightShader )
 		self.assertEqual( root.child( "cylinderLight" ).readAttribute( "light", 0 ), cylinderLightShader )
 
+	def testModelBound( self ) :
+
+		fileName = os.path.join( self.temporaryDirectory(), "modelBound.usda" )
+
+		stage = pxr.Usd.Stage.CreateNew( fileName )
+		pxr.UsdGeom.Xform.Define( stage, "/withoutModelAPI" )
+		pxr.UsdGeom.Xform.Define( stage, "/withModelAPI" )
+		pxr.UsdGeom.Xform.Define( stage, "/withModelAPIAndExtent" )
+
+		pxr.UsdGeom.ModelAPI.Apply( stage.GetPrimAtPath( "/withModelAPI" ) )
+		modelAPI = pxr.UsdGeom.ModelAPI.Apply( stage.GetPrimAtPath( "/withModelAPIAndExtent" ) )
+		modelAPI.SetExtentsHint( [ ( 1, 2, 3 ), ( 4, 5, 6 ) ] )
+
+		stage.GetRootLayer().Save()
+		del stage
+
+		root = IECoreScene.SceneInterface.create( fileName, IECore.IndexedIO.OpenMode.Read )
+		self.assertFalse( root.hasBound() )
+
+		self.assertFalse( root.child( "withoutModelAPI" ).hasBound() )
+		self.assertFalse( root.child( "withModelAPI" ).hasBound() )
+		self.assertTrue( root.child( "withModelAPIAndExtent" ).hasBound() )
+		self.assertEqual( root.child( "withModelAPIAndExtent" ).readBound( 0 ), imath.Box3d( imath.V3d( 1, 2, 3 ), imath.V3d( 4, 5, 6 ) ) )
+
+	def testPerPurposeModelBound( self ) :
+
+		fileName = os.path.join( self.temporaryDirectory(), "testPerPurposeModelBound.usda" )
+
+		stage = pxr.Usd.Stage.CreateNew( fileName )
+		pxr.UsdGeom.Xform.Define( stage, "/group" )
+		cube = pxr.UsdGeom.Cube.Define( stage, "/group/proxy" )
+		cube.CreatePurposeAttr().Set( "proxy" )
+
+		bboxCache = pxr.UsdGeom.BBoxCache( pxr.Usd.TimeCode( 0 ), [ "default", "render", "proxy", "guide" ] )
+		modelAPI = pxr.UsdGeom.ModelAPI.Apply( stage.GetPrimAtPath( "/group" ) )
+		modelAPI.SetExtentsHint( modelAPI.ComputeExtentsHint( bboxCache ) )
+
+		stage.GetRootLayer().Save()
+		del stage
+
+		root = IECoreScene.SceneInterface.create( fileName, IECore.IndexedIO.OpenMode.Read )
+		self.assertFalse( root.hasBound() )
+
+		self.assertTrue( root.child( "group" ).hasBound() )
+		self.assertEqual( root.child( "group" ).readBound( 0 ), imath.Box3d( imath.V3d( -1 ), imath.V3d( 1 ) ) )
+
 if __name__ == "__main__":
 	unittest.main()