From Colin MacDonald, "In my application I have a custom graphics context class, derived from

osg::GraphicsContext, in order to give good integration with the
application's GUI toolkit.  This works really well.

However, I need to share OpenGL texture resources with the standard
osgViewer GraphicsContext implementations, in particular the
PixelBuffers.  This is essential for my application to conserve graphics
memory on low-end hardware.  Currently the standard osg implementations
will not share resources with another derived osg::GraphicsContext,
other than the pre-defined osgViewer classes e.g. PixelBufferX11 is
hardcoded to only share resources with GraphicsWindowX11 and
PixelBufferX11 objects, and no other osg::GraphicsContext object.

To address this in the cleanest way I could think of, I have moved the
OpenGL handle variables for each platform into a small utility class,
e.g. GraphicsHandleX11 for unix.  Then GraphicsWindowX11, PixelBufferX11
and any other derived osg::GraphicsContext class can inherit from
GraphicsHandleX11 to share OpenGL resources.

I have updated the X11, Win32 and Carbon implementations to use this.
The changes are minor.  I haven't touched the Cocoa implmentation as
I'm not familiar with it at all and couldn't test it - it will work
unchanged.

Without this I had some horrible hacks in my application, this greatly
simplifies things for me.  It also simplifies the osgViewer
implementations slightly.  Perhaps it may help with other users'
desires to share resources with external graphics contexts, as was
discussed on the user list recently."

Notes from Robert Osfield, adapted Colin's submission to work with the new EGL related changes.

include/osgViewer/api/Carbon/GraphicsHandleCarbon

@@ -0,0 +1,50 @@
+/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2009 Robert Osfield 
+ *
+ * This library is open source and may be redistributed and/or modified under  
+ * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or 
+ * (at your option) any later version.  The full license is in LICENSE file
+ * included with this distribution, and on the openscenegraph.org website.
+ * 
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
+ * OpenSceneGraph Public License for more details.
+*/
+
+#ifndef OSGVIEWER_GRAPHICSHANDLECARBON
+#define OSGVIEWER_GRAPHICSHANDLECARBON 1
+
+#include <osgViewer/Export>
+
+#include <Carbon/Carbon.h>
+#include <AGL/agl.h>
+
+
+namespace osgViewer
+{
+
+/** Class to encapsulate platform-specific OpenGL context handle variables.
+  * Derived osg::GraphicsContext classes can inherit from this class to
+  * share OpenGL resources.*/
+
+class OSGVIEWER_EXPORT GraphicsHandleCarbon
+{
+    public:
+    
+        GraphicsHandleCarbon():
+            _context(0) {}
+
+        /** Set native AGL graphics context.*/        
+        inline void setAGLContext(AGLContext context) { _context = context; }
+
+        /** Get native AGL graphics context.*/        
+        inline AGLContext getAGLContext() const { return _context; }
+
+    protected:
+        
+        AGLContext      _context;
+};
+
+}
+
+#endif

include/osgViewer/api/Carbon/GraphicsWindowCarbon

@@ -22,12 +22,12 @@
 #if defined (__APPLE__) && (!__LP64__)
 
 #include <osgViewer/GraphicsWindow>
-#include <Carbon/Carbon.h>
-#include <AGL/agl.h>
+#include <osgViewer/api/Carbon/GraphicsHandleCarbon>
+
 namespace osgViewer
 {
 
-class GraphicsWindowCarbon : public osgViewer::GraphicsWindow
+class GraphicsWindowCarbon : public osgViewer::GraphicsWindow, public osgViewer::GraphicsHandleCarbon
 {
     public:
 
@@ -137,9 +137,6 @@ class GraphicsWindowCarbon : public osgViewer::GraphicsWindow
         /// install the standard os-eventhandler
         void installEventHandler();
         
-        /// get the AGL context
-        AGLContext getAGLContext() { return _context; }
-        
         // get the pixelformat
         AGLPixelFormat getAGLPixelFormat() { return _pixelFormat; }
         
@@ -159,7 +156,6 @@ class GraphicsWindowCarbon : public osgViewer::GraphicsWindow
 
         bool            _ownsWindow;
         WindowRef       _window;
-        AGLContext      _context;
         AGLPixelFormat  _pixelFormat;
         
         int             _windowTitleHeight;    

include/osgViewer/api/Carbon/PixelBufferCarbon

@@ -19,16 +19,13 @@
 #if defined (__APPLE__) && (!__LP64__)
 
 #include <osg/GraphicsContext>
-#include <osgViewer/Export>
-
-#include <Carbon/Carbon.h>
-#include <AGL/agl.h>
+#include <osgViewer/api/Carbon/GraphicsHandleCarbon>
 
 
 namespace osgViewer
 {
 
-class OSGVIEWER_EXPORT PixelBufferCarbon : public osg::GraphicsContext
+class OSGVIEWER_EXPORT PixelBufferCarbon : public osg::GraphicsContext, public osgViewer::GraphicsHandleCarbon
 {
     public:
 
@@ -37,8 +34,7 @@ class OSGVIEWER_EXPORT PixelBufferCarbon : public osg::GraphicsContext
             _initialized(false),
             _realized(false),
             _pixelformat(0),
-            _pbuffer(0),
-            _context(0)
+            _pbuffer(0)
         {
             _traits = traits;
 
@@ -91,10 +87,8 @@ class OSGVIEWER_EXPORT PixelBufferCarbon : public osg::GraphicsContext
 
         /** Swap the front and back buffers.*/
         virtual void swapBuffersImplementation();
-        
+       
         static AGLPixelFormat createPixelFormat(osg::GraphicsContext::Traits* traits);
-        
-        AGLContext getAGLContext() { return _context; }
 
     public:
     
@@ -112,9 +106,7 @@ class OSGVIEWER_EXPORT PixelBufferCarbon : public osg::GraphicsContext
         bool            _realized;
         
         AGLPixelFormat    _pixelformat;
-        AGLPbuffer        _pbuffer;
-        AGLContext        _context;
-        
+        AGLPbuffer        _pbuffer;        
 };
 
 }