RendererAlgo::objectSamples : Output single samples for static objects

Changes.md

@@ -8,6 +8,7 @@ Improvements
 - OSLShader :
  - Improved loading of spline parameters with additional duplicate endpoints.
  - Added support for loading splines from RenderMan shaders.
+- Rendering : Improved detection of static objects. This fixes messages from Arnold like "discarded X duplicate deformation keys", and may improve performance in some cases.
 
 Fixes
 -----

python/GafferSceneTest/RendererAlgoTest.py

@@ -61,6 +61,42 @@ def testObjectSamples( self ) :
 
 		self.assertEqual( [ s.radius() for s in samples ], [ 0.75, 1.25 ] )
 
+	def testObjectSamplesMatchingHash( self ) :
+
+		# If the input object has a hash that doesn't vary with time, then we just get one sample when
+		# we try to sample over time.
+		sphere = GafferScene.Sphere()
+		sphere["type"].setValue( sphere.Type.Primitive )
+
+		with Gaffer.Context() as c :
+			c["scene:path"] = IECore.InternedStringVectorData( [ "sphere" ] )
+			samples = GafferScene.Private.RendererAlgo.objectSamples( sphere["out"]["object"], [ 0.75, 1.25 ] )
+
+		self.assertEqual( [ s.radius() for s in samples ], [ 1.0 ] )
+
+	def testObjectSamplesMatchingResult( self ) :
+
+		# If the input object has different hashes at different times, but still produces identical objects,
+		# then we should still only output one sample.
+
+		frame = GafferTest.FrameNode()
+
+		# Quick hack to produce a value that doesn't vary, but has a hash that does: feed the frame
+		# through an integer multiply node, which will truncate the value to an integer
+		multiply = GafferTest.MultiplyNode()
+		multiply["op1"].setValue( 1 )
+		multiply["op2"].setInput( frame["output"] )
+
+		sphere = GafferScene.Sphere()
+		sphere["type"].setValue( sphere.Type.Primitive )
+		sphere["radius"].setInput( multiply["product"] )
+
+		with Gaffer.Context() as c :
+			c["scene:path"] = IECore.InternedStringVectorData( [ "sphere" ] )
+			samples = GafferScene.Private.RendererAlgo.objectSamples( sphere["out"]["object"], [ 1.25, 1.75 ] )
+
+		self.assertEqual( [ s.radius() for s in samples ], [ 1.0 ] )
+
 	def testNonInterpolableObjectSamples( self ) :
 
 		frame = GafferTest.FrameNode()

src/GafferScene/RendererAlgo.cpp

@@ -556,6 +556,9 @@ bool objectSamples( const ObjectPlug *objectPlug, const std::vector<float> &samp
 		const Context *frameContext = Context::current();
 		Context::EditableScope timeContext( frameContext );
 
+		bool actualMovement = false;
+		IECore::MurmurHash actualHash;
+
 		samples.reserve( sampleTimes.size() );
 		for( size_t i = 0; i < sampleTimes.size(); i++ )
 		{
@@ -568,6 +571,15 @@ bool objectSamples( const ObjectPlug *objectPlug, const std::vector<float> &samp
 				runTimeCast<const Camera>( object.get() )
 			)
 			{
+				if( i == 0 )
+				{
+					actualHash = object->hash();
+				}
+				else if( !actualMovement )
+				{
+					actualMovement = object->hash() != actualHash;
+				}
+
 				samples.push_back( object.get() );
 			}
 			else if(
@@ -608,6 +620,11 @@ bool objectSamples( const ObjectPlug *objectPlug, const std::vector<float> &samp
 				break;
 			}
 		}
+
+		if( !actualMovement && samples.size() > 1 )
+		{
+			samples.resize( 1 );
+		}
 	}
 
 	if( hash )