Major Description
This optimization would perform double-buffering in the viewport component (or skin) rather than copying the contents of the video buffer. The buffer would be restricted to the size of the viewport rather than the view.
The component can rebuild the buffer every time it is called to repaint (or possibly limit to updating the repaint region?). When the viewport top left or bottom right changes, the component can paint the unaffected area into the new buffer, then only repaint the affected area.
This optimization will allow content to be painted on top of a scroll pane, which the current optimization does not support (e.g. non-modal dialogs and watermark decorators do not work with the existing optimization).