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/X11/GraphicsHandleX11

@@ -0,0 +1,80 @@
+/* -*-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_GRAPHICSHANDLEX11
+#define OSGVIEWER_GRAPHICSHANDLEX11 1
+
+#include <osgViewer/Export>
+
+
+#if defined(OSG_GLES1_AVAILABLE) || defined(OSG_GLES2_AVAILABLE)
+    #define OSG_USE_EGL
+    #include <X11/X.h>
+    #include <X11/Xlib.h>
+    #include <X11/Xutil.h>
+    #include <EGL/egl.h>
+#else
+    #define GLX_GLXEXT_PROTOTYPES  1
+    #include <X11/X.h>
+    #include <X11/Xlib.h>
+    #include <X11/Xutil.h>
+    #include <GL/glx.h>
+    #ifndef GLX_VERSION_1_3
+        typedef XID GLXPbuffer;
+    #endif
+#endif
+
+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 GraphicsHandleX11
+{
+    public:
+    
+        GraphicsHandleX11():
+            _display(0),
+            _context(0) {}
+
+        /** Set X11 display.*/        
+        inline void setDisplay(Display* display) { _display = display; }
+
+        /** Get X11 display.*/        
+        inline Display* getDisplay() const { return _display; }
+
+        #ifdef OSG_USE_EGL
+            typedef EGLContext Context;
+            typedef EGLSurface Pbuffer;
+        #else
+            typedef GLXContext Context;
+            typedef GLXPbuffer Pbuffer;
+        #endif
+
+        /** Set native OpenGL graphics context.*/
+        inline void setContext(Context context) { _context = context; }
+
+        /** Get native OpenGL graphics context.*/        
+        inline Context getContext() const { return _context; }
+
+    protected:
+        
+        Display*        _display;
+        Context         _context;
+};
+
+}
+
+#endif

include/osgViewer/api/X11/GraphicsWindowX11

@@ -20,38 +20,23 @@
 #define OSGVIEWER_GRAPHICSWINDOWX11 1
 
 #include <osgViewer/GraphicsWindow>
-
-#define GLX_GLXEXT_PROTOTYPES  1
-
-#include <X11/X.h>
-#include <X11/Xlib.h>
-#include <X11/Xutil.h>
-
-#if defined(OSG_GLES1_AVAILABLE) || defined(OSG_GLES2_AVAILABLE) 
-    #define OSG_USE_EGL
-    #include <EGL/egl.h>
-#else
-    #include <GL/glx.h>
-#endif
-
+#include <osgViewer/api/X11/GraphicsHandleX11>
 
 #include <string.h>
 
 namespace osgViewer
 {
 
-class OSGVIEWER_EXPORT GraphicsWindowX11 : public osgViewer::GraphicsWindow
+class OSGVIEWER_EXPORT GraphicsWindowX11 : public osgViewer::GraphicsWindow, public osgViewer::GraphicsHandleX11
 {
     public:
 
         GraphicsWindowX11(osg::GraphicsContext::Traits* traits):
             _valid(false),
-            _display(0),
             _eventDisplay(0),
             _parent(0),
             _window(0),
             _visualInfo(0),
-            _context(0),
             #ifdef OSG_USE_EGL
             _eglDisplay(0),
             _eglSurface(0),
@@ -151,7 +136,6 @@ class OSGVIEWER_EXPORT GraphicsWindowX11 : public osgViewer::GraphicsWindow
     
         // X11 specific aces functions
 
-        Display* getDisplay() const { return _display; }
         Display* getEventDisplay() const { return _eventDisplay; }
         Display* getDisplayToUse() const ;
 
@@ -159,15 +143,6 @@ class OSGVIEWER_EXPORT GraphicsWindowX11 : public osgViewer::GraphicsWindow
         Window& getParent() { return _parent; }
         Window& getWindow() { return _window; }
 
-
-        #ifdef OSG_USE_EGL
-        typedef EGLContext Context;
-        #else
-        typedef GLXContext Context;
-        #endif
-
-        Context& getContext() { return _context; }
-
         Cursor getCurrentCursor() { return _currentCursor; }
 
     protected:
@@ -197,12 +172,10 @@ class OSGVIEWER_EXPORT GraphicsWindowX11 : public osgViewer::GraphicsWindow
         void flushKeyEvents();
         
         bool            _valid;
-        Display*        _display;
         Display*        _eventDisplay;
         Window          _parent;
         Window          _window;
         XVisualInfo*    _visualInfo;
-        Context         _context;
 
         #ifdef OSG_USE_EGL
         EGLDisplay      _eglDisplay;

include/osgViewer/api/X11/PixelBufferX11

@@ -19,18 +19,13 @@
 #ifndef OSGVIEWER_PIXELBUFFERX11
 #define OSGVIEWER_PIXELBUFFERX11 1
 
-#include <osgViewer/api/X11/GraphicsWindowX11>
-
-#ifndef OSG_USE_EGL
-    #ifndef GLX_VERSION_1_3
-        typedef XID GLXPbuffer;
-    #endif
-#endif
+#include <osg/GraphicsContext>
+#include <osgViewer/api/X11/GraphicsHandleX11>
 
 namespace osgViewer
 {
 
-class OSGVIEWER_EXPORT PixelBufferX11 : public osg::GraphicsContext
+class OSGVIEWER_EXPORT PixelBufferX11 : public osg::GraphicsContext, public osgViewer::GraphicsHandleX11
 {
     public:
 
@@ -69,19 +64,8 @@ class OSGVIEWER_EXPORT PixelBufferX11 : public osg::GraphicsContext
     public:
     
         // X11 specific aces functions
-
-        Display* getDisplay() const { return _display; }
         
-        #ifdef OSG_USE_EGL
-            typedef EGLContext Context;
-            typedef EGLSurface Pbuffer;
-        #else
-            typedef GLXContext Context;
-            typedef GLXPbuffer Pbuffer;
-        #endif
-
         Pbuffer& getPbuffer() { return _pbuffer; }
-        Context& getContext() { return _context; }
 
     protected:
     
@@ -92,10 +76,8 @@ class OSGVIEWER_EXPORT PixelBufferX11 : public osg::GraphicsContext
         void init();
 
         bool            _valid;
-        Display*        _display;
         Pbuffer         _pbuffer;
         XVisualInfo*    _visualInfo;
-        Context         _context;
 
         bool            _initialized;
         bool            _realized;