Content Backgrounds

To date little has changed in the graphics system. This is likely to change in the near future. One small modification that has occured is a change to the redraw protocol for plots. Originally, the protocol called for a :redraw-content method to erase and redraw a plot's content. The erasing part has now been split out into a separate :clear-content method which is called before :redraw-content. Methods for :redraw-content should now assume that the content has been cleared. This change allows a plot to maintain a background image by defining a suitable clear-content method. As a very simple example, the definition

(defmeth p :clear-content ()
  (call-next-method)
  (let ((col (send self :draw-color)))
    (send self :draw-color 'red)
    (send self :paint-rect 50 50 100 100)
    (send self :draw-color col)))

maintains a red rectangle in the background of a plot. More useful examples might be to include a histogram, a function, or a map in the background.