Improved support for texture subload/render to texture in various Texture classes

and RenderStage.

src/osg/TextureRectangle.cpp

@@ -193,6 +193,28 @@ void TextureRectangle::apply(State& state) const
             non_const_this->_image = 0;
         }
     }
+    else if ( (_textureWidth!=0) && (_textureHeight!=0) && (_internalFormat!=0) )
+    {
+        _textureObjectBuffer[contextID] = textureObject = generateTextureObject(
+                contextID,GL_TEXTURE_RECTANGLE,0,_internalFormat,_textureWidth,_textureHeight,1,0);
+        
+        textureObject->bind();
+
+        applyTexParameters(GL_TEXTURE_RECTANGLE,state);
+
+        // no image present, but dimensions at set so lets create the texture
+        glTexImage2D( GL_TEXTURE_RECTANGLE, 0, _internalFormat,
+                     _textureWidth, _textureHeight, _borderWidth,
+                     _internalFormat,
+                     GL_UNSIGNED_BYTE,
+                     0);                
+                     
+        if (_readPBuffer.valid())
+        {
+            _readPBuffer->bindPBufferToTexture(GL_FRONT);
+        }
+        
+    }
     else
     {
         glBindTexture(GL_TEXTURE_RECTANGLE, 0);