Checkpoint, I've got an interactive 2d scene mostly working.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@4151 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/as/com/threerings/presents/dobj/CompoundEvent.as

@@ -40,8 +40,14 @@ public class CompoundEvent extends DEvent
     /**
      * Constructs a compound event and prepares it for operation.
      */
-    public function CompoundEvent (target :DObject, omgr :DObjectManager)
+    public function CompoundEvent (
+            target :DObject = null, omgr :DObjectManager = null)
     {
+        if (target == null) {
+            super();
+            return;
+        }
+
         super(target.getOid());
 
         // sanity check

src/as/com/threerings/presents/dobj/DEvent.as

@@ -10,7 +10,7 @@ import com.threerings.util.StringBuilder;
 public /* abstract */ class DEvent
     implements Streamable
 {
-    public function DEvent (targetOid :int)
+    public function DEvent (targetOid :int = 0)
     {
         _toid = targetOid;
     }