Added GraphicsContext support for clearing the graphis context. The clearing

is off by default (ClearMask is 0), but can be switched on when ClearMask is
non zero.  GraphicsContext::clear() is called after each swap buffers

examples/osghangglide/osghangglide.cpp

@@ -161,6 +161,11 @@ int main( int argc, char **argv )
             osg::notify(osg::NOTICE)<<"  GraphicsWindow has been created successfully."<<gw<<std::endl;
 
             gw->getEventQueue()->getCurrentEventState()->setWindowRectangle(0, 0, width, height );
+            
+            // need to ensure that the window is cleared make sure that the complete window is set the correct colour
+            // rather than just the parts of the window that are under the camera's viewports
+            gw->setClearColor(osg::Vec4f(0.2f,0.2f,0.6f,1.0f));
+            gw->setClearMask(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
         }
         else
         {

include/osg/GraphicsContext

@@ -169,6 +169,9 @@ class OSG_EXPORT GraphicsContext : public Referenced
         /** Get the traits of the GraphicsContext.*/
         inline const Traits* getTraits() const { return _traits.get(); }
 
+        /** Return whether a valid and usable GraphicsContext has been created.*/
+        virtual bool valid() const { return false; }
+
 
         /** Set the State object which tracks the current OpenGL state for this graphics context.*/
         inline void setState(State* state) { _state = state; }
@@ -178,10 +181,25 @@ class OSG_EXPORT GraphicsContext : public Referenced
         
         /** Get the const State object which tracks the current OpenGL state for this graphics context.*/
         inline const State* getState() const { return _state.get(); }
-        
 
-        /** Return whether a valid and usable GraphicsContext has been created.*/
-        virtual bool valid() const { return false; }
+
+        /** Sets the clear color. */
+        inline void setClearColor(const Vec4& color) { _clearColor = color; }
+
+        /** Returns the clear color. */
+        inline const Vec4& getClearColor() const { return _clearColor; }
+        
+        /** Set the clear mask used in glClear(..).
+          * Defaults to GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT. */
+        inline void setClearMask(GLbitfield mask) { _clearMask = mask; }
+
+        /** Get the clear mask.*/
+        inline GLbitfield getClearMask() const { return _clearMask; }
+        
+        /** Do an OpenGL clear of the full graphics context/window.
+          * Note, must only be called from a thread with this context current.*/
+        virtual void clear();
+        
 
         /** Realise the GraphicsContext.*/
         bool realize();
@@ -288,6 +306,10 @@ class OSG_EXPORT GraphicsContext : public Referenced
 
         ref_ptr<Traits>         _traits;        
         ref_ptr<State>          _state;
+
+        Vec4                    _clearColor;
+        GLbitfield              _clearMask;
+
         OpenThreads::Mutex      _mutex;
         OpenThreads::Thread*    _threadOfLastMakeCurrent;
         

src/osg/GraphicsContext.cpp

@@ -126,6 +126,8 @@ void GraphicsContext::decrementContextIDUsageCount(unsigned int contextID)
 
 
 GraphicsContext::GraphicsContext():
+    _clearColor(osg::Vec4(0.0f,0.0f,0.0f,1.0f)),
+    _clearMask(0),
     _threadOfLastMakeCurrent(0)
 {
     setThreadSafeRefUnref(true);
@@ -137,7 +139,18 @@ GraphicsContext::~GraphicsContext()
     close(false);
 }
 
-/** Realise the GraphicsContext.*/
+void GraphicsContext::clear()
+{
+    if (_clearMask==0 || !_traits) return;
+
+    glViewport(0, 0, _traits->width, _traits->height);
+    glScissor(0, 0, _traits->width, _traits->height);
+
+    glClearColor( _clearColor[0], _clearColor[1], _clearColor[2], _clearColor[3]);
+
+    glClear( _clearMask );
+}
+
 bool GraphicsContext::realize()
 {
     if (realizeImplementation())
@@ -212,6 +225,7 @@ void GraphicsContext::swapBuffers()
     if (isCurrent())
     {
         swapBuffersImplementation();
+        clear();
     }
     else if (_graphicsThread.valid() && 
              _threadOfLastMakeCurrent == _graphicsThread.get())
@@ -222,6 +236,7 @@ void GraphicsContext::swapBuffers()
     {
         makeCurrent();
         swapBuffersImplementation();
+        clear();
         releaseContext();
     }
 }

src/osg/GraphicsThread.cpp

@@ -379,6 +379,7 @@ void SwapBuffersOperation::operator () (GraphicsContext* context)
     if (context)
     {
         context->swapBuffersImplementation();
+        context->clear();
     }
 }