Added State::glDrawBuffer/glReadBuffer() method to implement lazy state updating for glDrawBuffer and glReadBuffer

include/osg/State

@@ -303,6 +303,14 @@ class OSG_EXPORT State : public Referenced
         /** Apply any shader composed state.*/
         void applyShaderComposition();
 
+
+        void glDrawBuffer(GLenum buffer);
+        GLenum getDrawBuffer() const { return _drawBuffer; }
+
+        void glReadBuffer(GLenum buffer);
+        GLenum getReadBuffer() const { return _readBuffer; }
+
+
         /** Set whether a particular OpenGL mode is valid in the current graphics context.
           * Use to disable OpenGL modes that are not supported by current graphics drivers/context.*/
         inline void setModeValidity(StateAttribute::GLMode mode,bool valid)
@@ -1079,6 +1087,9 @@ class OSG_EXPORT State : public Referenced
 
         ref_ptr<FrameStamp>         _frameStamp;
 
+        GLenum                      _drawBuffer;
+        GLenum                      _readBuffer;
+
         ref_ptr<const RefMatrix>    _identity;
         ref_ptr<const RefMatrix>    _initialViewMatrix;
         ref_ptr<const RefMatrix>    _projection;

src/osg/State.cpp

@@ -51,6 +51,9 @@ State::State():
     _shaderComposer = new ShaderComposer;
     _currentShaderCompositionProgram = 0L;
 
+    _drawBuffer = GL_NONE;
+    _readBuffer = GL_NONE;
+
     _identity = new osg::RefMatrix(); // default RefMatrix constructs to identity.
     _initialViewMatrix = _identity;
     _projection = _identity;
@@ -434,6 +437,28 @@ void State::reset()
 
 }
 
+void State::glDrawBuffer(GLenum buffer)
+{
+    if (_drawBuffer!=buffer)
+    {
+        #if !defined(OSG_GLES1_AVAILABLE) && !defined(OSG_GLES2_AVAILABLE) && !defined(OSG_GLES3_AVAILABLE)
+        glDrawBuffer(buffer);
+        #endif
+        _drawBuffer=buffer;
+    }
+}
+
+void State::glReadBuffer(GLenum buffer)
+{
+    if (_readBuffer!=buffer)
+    {
+        #if !defined(OSG_GLES1_AVAILABLE) && !defined(OSG_GLES2_AVAILABLE) && !defined(OSG_GLES3_AVAILABLE)
+        glReadBuffer(buffer);
+        #endif
+        _readBuffer=buffer;
+    }
+}
+
 void State::setInitialViewMatrix(const osg::RefMatrix* matrix)
 {
     if (matrix) _initialViewMatrix = matrix;