From Jan Peciva, "please find attached proposed fix for ON_DEMAND rendering. The biggest issue was

that the windows did not act on repaint request (WM_PAINT, EXPOSE,...)

Detailed explanation:
- I implemented requestRedraw using the push approach (not using
GraphicsWindow::_requestRedraw flag that I was considering) as there may be
multiple viewers reading the flag and fighting to reset it after the paint
request, while some viewers may not spot the request to redraw
- I made windows call GraphicsWindow::requestRedraw when they receive
appropriate message (WM_PAINT, EXPOSE, RESIZE,...)
- There were issues on Linux that windows did not want to close using x
button. Resolved by moving the test for DeleteWindow event from
swapBuffersImplementation() to GraphicsWindowX11::checkEvents(). The difficulty
was that DeleteWindow event is not coming using _eventDisplay, but through
_display.
- The last difficulty was that it is necessary to call
ViewerBase::checkWindowStatus() to set _done to true when all windows are
closed. This did not happened recently in ON_DEMAND run scheme. I put the call
to checkWindowStatus() to eventTraversal.
"

include/osgViewer/ViewerBase

@@ -195,9 +195,6 @@ class OSGVIEWER_EXPORT ViewerBase : public virtual osg::Object
         osgUtil::IncrementalCompileOperation* getIncrementalCompileOperation() { return _incrementalCompileOperation.get(); }
 
 
-        /** Check to see if windows are still open, if not set viewer done to true. */
-        void checkWindowStatus();
-
         enum FrameScheme
         {
             ON_DEMAND,
@@ -253,6 +250,15 @@ class OSGVIEWER_EXPORT ViewerBase : public virtual osg::Object
         typedef std::vector<osgViewer::View*> Views;
         virtual void getViews(Views& views, bool onlyValid=true) = 0;
 
+        /** Check to see if any windows are still open. If not, set viewer done to true. */
+        void checkWindowStatus();
+
+        /** Check to see if windows are still open using the list of contexts given as a parameter.
+         *  If no windows are open, stop rendering threads and set viewer done to true.
+         *  This function is more effective than checkWindowStatus() as it does not query
+         *  the context list and should be used whenever context list is already available in your code.*/
+        void checkWindowStatus(const Contexts& contexts);
+
         virtual double elapsedTime() = 0;
 
         virtual osg::FrameStamp* getViewerFrameStamp() = 0;