diff --git a/include/osg/BufferObject b/include/osg/BufferObject
index 2829ec14d..e14d383f2 100644
--- a/include/osg/BufferObject
+++ b/include/osg/BufferObject
@@ -68,9 +68,29 @@
 
 #endif
 
+#ifndef GL_VERSION_1_5
+    #define GL_STREAM_DRAW                    0x88E0
+    #define GL_STREAM_READ                    0x88E1
+    #define GL_STREAM_COPY                    0x88E2
+    #define GL_STATIC_DRAW                    0x88E4
+    #define GL_STATIC_READ                    0x88E5
+    #define GL_STATIC_COPY                    0x88E6
+    #define GL_DYNAMIC_DRAW                   0x88E8
+    #define GL_DYNAMIC_READ                   0x88E9
+    #define GL_DYNAMIC_COPY                   0x88EA
+#endif
+
+#ifndef GL_VERSION_2_1
+    #define GL_PIXEL_PACK_BUFFER              0x88EB
+    #define GL_PIXEL_UNPACK_BUFFER            0x88EC
+    #define GL_PIXEL_PACK_BUFFER_BINDING      0x88ED
+    #define GL_PIXEL_UNPACK_BUFFER_BINDING    0x88EF
+#endif
+
+
 #ifndef GL_ARB_pixel_buffer_object
-    #define GL_PIXEL_PACK_BUFFER_ARB          0x88EB
-    #define GL_PIXEL_UNPACK_BUFFER_ARB        0x88EC
+    #define GL_PIXEL_PACK_BUFFER_ARB            0x88EB
+    #define GL_PIXEL_UNPACK_BUFFER_ARB          0x88EC
     #define GL_PIXEL_PACK_BUFFER_BINDING_ARB    0x88ED
     #define GL_PIXEL_UNPACK_BUFFER_BINDING_ARB  0x88EF
 #endif
diff --git a/include/osg/Camera b/include/osg/Camera
index 43f8750bf..1225091d7 100644
--- a/include/osg/Camera
+++ b/include/osg/Camera
@@ -443,8 +443,10 @@ class OSG_EXPORT Camera : public Transform, public CullSettings
 
             META_Object(osg,DrawCallback)
         
+            /** Functor method called by rendering thread. Users will typically override this method to carry tasks such as screen capture.*/
             virtual void operator () (osg::RenderInfo& renderInfo) const;
 
+            /** Functor method, provided for backwards compatibility, called by operator() (osg::RenderInfo& renderInfo) method.*/
             virtual void operator () (const osg::Camera& /*camera*/) const {}
         };