One omission in canvas functionality is the lack of relief effects for canvas objects. This makes anything drawn on a canvas seem flat in comparison to the relief effects incorporated in the surrounding widgets.
In the case of the network topology window shown in Figure 2, we use sunken rectangles to represent the three buffers at each switch output port. To simulate this effect, we embed other canvas windows in the main canvas. This allows us to set a sunken relief effect on the embedded canvas, which gives the effect of a sunken bar graph. While this works for creating reliefed rectangles, other shapes cannot be created in this way. In addition, the complete canvas window can no longer be printed through the canvas postscript method because embedded windows are ignored. The generated PostScript has holes wherever an embedded window appears on the screen.