Mastering Perl/Tk

Pie Menus

We are accustomed to using one-dimensional linear menus—not one-dimensional in appearance, but in usage. When a linear menu is posted, the cursor is positioned at the top of the menu and we are expected to move the cursor downward. If we overshoot the target menu item, we can move the cursor upward, but we’re still moving in a single dimension. As the cursor moves over menu items, their reliefs change (unless disabled) to raised, meaning they are activated. To actually invoke a menu item we must release button 1 while the cursor is within the area defined by the menu item.

In contrast, pie menus are two dimensional: the cursor is initially positioned in the center of the pie, so all the wedge-shaped menu items are the same distance from the cursor but in different directions. Thus all menu items are equally accessible, spatially. Each pie piece has a virtual section that extends from the pie’s perimeter to the edge of the display. To hit such a large target requires a gross, gestural motor movement, which your muscles easily learn and remember.

Pie menus were invented by Don Hopkins. For a history of Don’s work, visit http://catalog.com/hopkins/piemenus/index.html. This experimental Perl/Tk pie menu implementation is based on a piece of Don’s early work, written in 1992 for an early version of Tcl/Tk.

Figure 12-11 illustrates what a File pie menu might look like. The pie menu has six menu items, each occupying a 60 degree slice of the pie. To select an item, we ...