Pie menus

In computer interface design, a pie menu (also known as a radial menu) is a circular context menu where selection depends on direction. It is a graphical control element. A pie menu is made of several "pie slices" around an inactive center and works best with stylus input, and well with a mouse. Pie slices are drawn with a hole in the middle for an easy way to exit the menu.

Pie menus work well with keyboard acceleration, particularly four and eight item menus, on the cursor keys and the number pad. A goal of pie menus is to provide a smooth, reliable gestural style of interaction for novices and experts. A slice can lead to another pie menu; selecting this may center the pointer in the new menu.

A marking menu is a variant of this technique that makes the menu less sensitive to variance in gesture size.

As a kind of context menu, pie menus are often context-sensitive, showing different options depending on what the pointer was pointing at when the menu was requested.

The first documented radial menu is attributed to a system called PIXIE in 1969. Some universities explored alternative visual layouts.

In 1986, Mike Gallaher and Don Hopkins together independently arrived at the concept of a context menu based on the angle to the origin where the exact angle and radius could be passed as parameters to a command, or the radius could be used to trigger a submenu.

The first performance comparison to linear menus was performed in 1988 showing an increase in performance of 15% less time and a reduction of selection errors.

For novice users, pie menus are easy because they are a self-revealing gestural interface: They show what you can do and direct you how to do it. By clicking and popping up a pie menu, looking at the labels, moving the pointer in the desired direction, then clicking to make a selection, users learn the menu and practice the gesture to "mark ahead" ("mouse ahead" in the case of a mouse, "wave ahead" in the case of a dataglove). With a little practice, it becomes quite easy to mark ahead even through nested pie menus.

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