Advanced Perl Programming

Geometry Management

You’ve already seen the purpose of the pack method. The name of the game is “geometry management,” the art of arranging widgets on the screen and specifying a policy for rearranging themselves when the screen is resized. Tk supports three types of geometry managers: placer, packer, and grid. The placer is the simplest of the lot. Like Motif’s Bulletin Board widget or Visual Basic’s geometry management policy, you have to specify the x and y coordinates of each widget. I’ll just refer you to the Tk documentation for more details on the placer.

Packer

The packer, like Motif’s Form widget, is a powerful constraint-based geometry manager. The packer is not an object; it is simply the algorithm implemented by the pack() method. In other words, the call $widget—>pack() is a request to the widget to pack itself in the next available space inside its containing widget.

When you pack a suitcase, you typically start at one end and, for every item, proceed to fill in the remaining space. The packer works exactly like this, but there’s one crucial difference. Once it sticks a widget onto an edge of a container widget, it slices off that entire edge and takes it off the remaining available space. Figure 14.10 illustrates the packing algorithm.

Figure 14-10. Packing algorithm

In this figure, if the side were specified as top or bottom, the height of the label would dictate the ...