A slice can lead to another pie menu; selecting this may center the mouse cursor in the new menu.
Pie menus are often context-sensitive, showing different options depending on what the mouse cursor was pointing at when the menu was requested.
Pie menus are drawn as pie slices with a hole in the middle for an easy way to exit the menu.
Pie menus are faster and more reliable to select from than linear menus, because selection depends on direction instead of distance. The circular menu slices are large in size and near the pointer for fast interaction (see Fitts's law). Experienced users use muscle memory without looking at the menu while selecting from it Nested pie menus can efficiently offer many options, and some pie menus can pop up linear menus, and combine linear and radial items in the same menu Pie menus just like any popup menu are shown only when requested, resulting in less visual distraction and clutter than toolbars and menu bars that are always shown.
Pie menus come with a higher cognitive load, because of the use of higher order cognitive processes associated with recollection than with visual navigation. This is due to both the fact that limitations on our memory in terms of serial processing and items we are able to hold in our short term memory are much fewer than our visual motor are able to handle.
Pie menus show available options, in contrast to invisible mouse gestures. Pie menus that delay appearance until the cursor stops moving reduce intrusiveness to the same level as mouse gestures and pie menus for experienced users. Pie menus take up more screen space than linear menus, and the number of slices in an individual menu must be kept low for effectiveness by using submenus. When using pie menus, submenus may overlap with the parent menu, but the parent menu may become translucent or hidden.
Pie menus are most suited for actions that have been laid out by humans, and have logical grouping choices. Linear menus are most suited for dynamic, large menus that have many possible options, without any logical grouping. However, using interaction techniques that are not pointer based have proven problematic with both pie and linear menues.
For the novice, 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 cursor in the desired direction, then clicking to make a selection, you 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.
For the expert, they're efficient because—without even looking—you can move in any direction, and mark ahead so fast that the menu doesn't even pop up. Only when used more slowly like a traditional menu, does a pie menu pop up on the screen, to reveal the available selections.
Most importantly, novices soon become experts, because every time you select from a pie menu, you practice the motion to mark ahead, so you naturally learn to do it by feel. As Jaron Lanier of VPL Research has remarked, "The mind may forget, but the body remembers." Pie menus take advantage of the body's ability to remember muscle motion and direction, even when the mind has forgotten the corresponding symbolic labels.
Exit by clicking the center.
Expert (rely on muscle memory):
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