From Stephan Huber, "I added a bool to GraphicsContext::Traits to indicate wether to use the

multithreaded-opengl-engine on os x or not. I set its default to false,
perhaps other os x users can test this setting with their data/apps, to
see if we can enable it by default.

I changed also the borderless-window-type, so expos?works correctly."

include/osg/GraphicsContext

@@ -75,6 +75,7 @@ class OSG_EXPORT GraphicsContext : public Object
                 face(0),
                 mipMapGeneration(false),
                 vsync(true),
+                useMultiThreadedOpenGLEngine(false),
                 useCursor(true),
                 sharedContext(0) {}
                             
@@ -115,6 +116,9 @@ class OSG_EXPORT GraphicsContext : public Object
             // V-sync
             bool            vsync;
             
+            // use multithreaded OpenGL-engine (OS X only)
+            bool            useMultiThreadedOpenGLEngine;
+            
             // enable cursor
             bool            useCursor;