USD CameraAlgo : Only read authored shutter values from USD

This avoids cameras read from USD files ending up with USD's default [0, 0] shutter when the USD camera has no shutter values.

Author: murraystevenson

Changes

@@ -4,7 +4,9 @@
 Fixes
 -----
 
-- USDScene : Fixed writing of shutter values from cameras without a `shutter` parameter. The `shutter:open` and `shutter:close` attributes are now omitted instead of being written with Cortex's default -0.5, 0.5 shutter values.
+- USDScene :
+  - Fixed writing of shutter values from cameras without a `shutter` parameter. The `shutter:open` and `shutter:close` attributes are now omitted instead of being written with Cortex's default -0.5, 0.5 shutter values.
+  - Fixed reading of shutter values from cameras without `shutter:open` and `shutter:close` attributes. The `shutter` parameter is now omitted instead of being created with USD's default 0, 0 shutter values.
 
 10.5.x.x (relative to 10.5.15.0)
 ========

contrib/IECoreUSD/src/IECoreUSD/CameraAlgo.cpp

@@ -111,9 +111,14 @@ IECore::ObjectPtr readCamera( pxr::UsdGeomCamera &camera, pxr::UsdTimeCode time,
 	result->setFocusDistance( focusDistance );
 
 	Imath::V2d shutter;
-	camera.GetShutterOpenAttr().Get( &shutter[0], time );
-	camera.GetShutterCloseAttr().Get( &shutter[1], time );
-	result->setShutter( shutter );
+	auto shutterOpenAttr = camera.GetShutterOpenAttr();
+	auto shutterCloseAttr = camera.GetShutterCloseAttr();
+	if( shutterOpenAttr.HasAuthoredValue() || shutterCloseAttr.HasAuthoredValue() )
+	{
+		shutterOpenAttr.Get( &shutter[0], time );
+		shutterCloseAttr.Get( &shutter[1], time );
+		result->setShutter( shutter );
+	}
 
 	return result;
 }

contrib/IECoreUSD/test/IECoreUSD/USDSceneTest.py

@@ -1400,6 +1400,7 @@ def assertVectorsAlmostEqual( a, b,**kw ) :
 			self.assertEqual( c2.getClippingPlanes(), c.getClippingPlanes() )
 			self.assertEqual( c2.getFStop(), c.getFStop() )
 			self.assertEqual( c2.getFocusDistance(), c.getFocusDistance() )
+			self.assertEqual( c2.hasShutter(), c.hasShutter() )
 			self.assertEqual( c2.getShutter(), c.getShutter() )
 
 			assertVectorsAlmostEqual( c2.frustum().min(), c.frustum().min(), places = 6 )