GafferScene : Enable "USDPointInstancerAdaptor"

Changes.md

@@ -5,6 +5,11 @@ Features
 --------
 
 - AttributeEditor, LightEditor, RenderPassEditor : Added drag and drop editing. Edits can be created or updated by dropping a value into a cell. Cells representing a set expression or string array can be modified by holding <kbd>Shift</kbd> to append to an existing edit, or <kbd>Control</kbd> may be held to remove from an existing edit.
+- USD : Added automatic expansion of USD PointInstancers at render time.
+  - This can be controlled on a per-instancer basis using a `gafferUSD:pointInstancerAdaptor:enabled` boolean attribute.
+  - Which point cloud primitive variables are promoted to user attributes can be controlled using a `gafferUSD:pointInstancerAdaptor:attributes` string attribute.
+  - May be disabled entirely with `GafferScene.SceneAlgo.deregisterRenderAdaptor( "USDPointInstancerAdaptor" )`.
+- Viewer : Added "Expand USD Instancers" item to the Expansion menu. Defaults to on for all renderers except OpenGL.
 
 Fixes
 -----

startup/GafferScene/usdPointInstancerAdaptor.py

@@ -40,10 +40,16 @@
 # into actual Instancers. This supports how USD PointInstancers are currently loaded from
 # USD files. In the future, they may be first class objects, and this will be unnecessary.
 
-try:
-	import GafferUSD
-	# Disabled while we work on a solution for automatically remapping prototype paths
-	# when pointclouds have been reparented in the scene hierarchy.
-	# GafferScene.SceneAlgo.registerRenderAdaptor( "USDPointInstancerAdaptor", GafferUSD._PointInstancerAdaptor, "SceneView *Render", "*" )
-except ImportError :
-	pass
+# We don't want to create a dependency on GafferUSD - this should silently do nothing if GafferUSD
+# isn't available. We also don't want to import GafferUSD right away - that could lead to circular
+# import problems. So instead we register this callback that will try to import GafferUSD
+def createPointInstancerAdaptor():
+	try:
+		import GafferUSD
+		return GafferUSD._PointInstancerAdaptor()
+	except ImportError :
+		r = GafferScene.SceneProcessor()
+		r["out"].setInput( r["in"] )
+		return r
+
+GafferScene.SceneAlgo.registerRenderAdaptor( "USDPointInstancerAdaptor", createPointInstancerAdaptor, "SceneView *Render", "*" )