From Farshid Lashkari,

"I've made some changes to osg which I think make it easier to control
the render order of CameraNode's. Instead of using the built-in orders
(PRE_RENDER, POST_RENDER, NESTED_RENDER), you can specify an integer
order. Values less than zero are pre rendered in order. Values greater
than zero are post rendered in order. And a value of 0 is equivalent
to NESTED_RENDER.

The changes should be fully backward compatible. Also, I changed the
RenderStageList type from a vector to a list because I needed to be
able to insert values anywhere in the list.

The reason I made these changes was because I wanted to be able to set
the render order of a CameraNode at runtime without having to reorder
it in the scenegraph."

and later in the final submission message (relating to what has been finally been merged)    :

"I've rethought my implementation and came up with something a little
better. The setRenderOrder will continue to take an enum, but will
have an optional orderNum parameter which can be both positive and
negative. I think this method is more intuitive and flexible."

include/osg/CameraNode

@@ -181,11 +181,14 @@ class OSG_EXPORT CameraNode : public Transform, public CullSettings
         /** Set the rendering order of this camera's subgraph relative to any camera that this subgraph is nested within.
           * For rendering to a texture, one typically uses PRE_RENDER.
           * For Head Up Displays, one would typically use POST_RENDER.*/
-        void setRenderOrder(RenderOrder order) { _renderOrder = order; }
+        void setRenderOrder(RenderOrder order, int orderNum = 0) { _renderOrder = order; _renderOrderNum = orderNum; }
         
         /** Get the rendering order of this camera's subgraph relative to any camera that this subgraph is nested within.*/
         RenderOrder getRenderOrder() const { return _renderOrder; }
 
+        /** Get the rendering order number of this camera relative to any sibling cameras in this subgraph.*/
+        int getRenderOrderNum() const { return _renderOrderNum; }        
+
         /** Return true if this Camera is set up as a render to texture camera, i.e. it has textures assigned to it.*/
         bool isRenderToTextureCamera() const;
 
@@ -366,6 +369,7 @@ class OSG_EXPORT CameraNode : public Transform, public CullSettings
         Matrixd                     _viewMatrix;
         
         RenderOrder                 _renderOrder;
+        int                         _renderOrderNum;
         
         GLenum                      _drawBuffer;
         GLenum                      _readBuffer;