SceneAlgo : ObjectProcessor object history fix

Fixes #5406.

Changes.md

@@ -25,6 +25,7 @@ Fixes
 - Reference : Fixed rare reloading error.
 - PlugLayout : Fixed lack of update when `layout:customWidget:*` metadata changes.
 - Dispatch app : Removed unnecessary and misleading "Execute" button.
+- SceneAlgo : Fixed computation of `ScenePlug.object` in networks with nodes derived from `ObjectProcessor`. These include : `CameraTweaks`, `ClosestPointSampler`, `CollectPrimitiveVariables`, `CopyPrimitiveVariables`, `CurveSampler`, `DeleteCurves`, `DeleteFaces`, `DeletePoints`, `MapOffset`, `MapProjection`, `MeshDistortion`, `MeshNormals`, `MeshSegments`, `MeshTangents`, `MeshToPoints`, `MeshType`, `Orientation`, `PointsType`, `PrimitiveSampler`, `PrimitiveVariables`, `ReverseWinding`, `ShufflePrimitiveVariables` and `UVSampler` (#5406).
 
 API
 ---

python/GafferSceneTest/SceneAlgoTest.py

@@ -404,6 +404,38 @@ def testHistoryPerformanceAlreadyCached( self ) :
 			h = h.predecessors[-1]
 		self.assertEqual( h.context["seed"], 5 )
 
+	def testObjectProcessorHistory( self ) :
+
+		plane = GafferScene.Plane()
+
+		meshType = GafferScene.MeshType()
+		meshType["in"].setInput( plane["out"] )
+
+		def runTest() :
+
+			history = GafferScene.SceneAlgo.history( meshType["out"]["object"], "/plane" )
+
+			for plug, scenePath in [
+				( meshType["out"], "/plane" ),
+				( meshType["in"], "/plane" ),
+				( plane["out"], "/plane" ),
+			] :
+				self.assertEqual( history.scene, plug )
+				self.assertEqual( GafferScene.ScenePlug.pathToString( history.context["scene:path"] ), scenePath )
+				history = history.predecessors[0] if history.predecessors else None
+
+			self.assertIsNone( history )
+
+		runTest()
+
+		# Test running the test while everything is already cached still works, and doesn't add any
+		# new entries to the cache
+		Gaffer.ValuePlug.clearHashCache()
+		runTest()
+		before = Gaffer.ValuePlug.hashCacheTotalUsage()
+		runTest()
+		self.assertEqual( Gaffer.ValuePlug.hashCacheTotalUsage(), before )
+
 	def testHistoryWithNoComputes( self ) :
 
 		switch = Gaffer.Switch()

src/GafferScene/SceneAlgo.cpp

@@ -400,6 +400,8 @@ struct CapturedProcess
 
 };
 
+const InternedString g_processedObjectPlugName( "__processedObject" );
+
 /// \todo Perhaps add this to the Gaffer module as a
 /// public class, and expose it within the stats app?
 /// Give a bit more thought to the CapturedProcess
@@ -432,7 +434,7 @@ class CapturingMonitor : public Monitor
 
 			CapturedProcess::Ptr capturedProcess;
 			ProcessOrScope entry;
-			if( !p->parent<ScenePlug>() || p->getName() != m_scenePlugChildName )
+			if( !shouldCapture( p ) )
 			{
 				// Parents may spawn other processes in support of the requested plug. This is one
 				// of these other plugs that isn't directly the requested plug.  Instead of creating
@@ -491,10 +493,7 @@ class CapturingMonitor : public Monitor
 
 		bool forceMonitoring( const Plug *plug, const IECore::InternedString &processType ) override
 		{
-			if(
-				processType == g_hashProcessType &&
-				plug->parent<ScenePlug>() && plug->getName() == m_scenePlugChildName
-			)
+			if( processType == g_hashProcessType && shouldCapture( plug ) )
 			{
 				return true;
 			}
@@ -504,6 +503,14 @@ class CapturingMonitor : public Monitor
 
 	private :
 
+		bool shouldCapture( const Plug *plug ) const
+		{
+			return
+				( plug->parent<ScenePlug>() && plug->getName() == m_scenePlugChildName ) ||
+				( (Gaffer::TypeId)plug->typeId() == Gaffer::TypeId::ObjectPlugTypeId && plug->getName() == g_processedObjectPlugName )
+			;
+		}
+
 		using Mutex = tbb::spin_mutex;
 
 		Mutex m_mutex;