How to Choose with Pie Menus

Don Hopkins
University of Maryland
Human Computer Interaction Lab

Jack Callahan
University of Maryland
Heterogeneous Systems Lab

Pie menus have their choices positioned in a circle around the menu center.

Pressing a mouse button pops up a menu, with the cursor initially located
in a small inactive region at the menu center.

Each choice is adjacent to the cursor, but in a different direction. 

Moving the cursor in the direction of one of the choices highlights
its label.

Clicking the mouse button selects the currently hightlighted item.

Selection is defined by the direction of relative cursor motion
between button clicks. 

The selection accuracy becomes more precise as the cursor moves 
further away from the menu center. 

The distance may also serve as a parameter to the choice.

The circular layout of a pie menu is very appropriate for certian 
applications:

Spatially oriented items can be placed in their corresponding
directions.

[Compass Menu]
[Binary Tree Menu]

Pairs of complementary items can be placed in opposite directions.

[Confirmation Menu]
[Zoom Menu]

Other natural and intuitive arrangments are possible.

[Week Days Menu]
[Hour Menu]

Selecting without seeing:

Pie menus do not require a lot of visual attention to use,
because they are based on direction of relative mouse movement, instead
of absolute cursor positioning.

An experienced pie menu user can make selections quite reliably from a
familiar, reasonably sized menu, without even looking at the display!

Mouse ahead:

Pie menus work very well with mouse ahead!
Mouse ahead is when the user gives commands to the computer with the 
mouse more quickly than the computer can process, but instead of the 
computer ignoring the commands, it buffers them, and processes them 
all in order.

Because it possible to use a pie menu without seeing it,
experienced pie menu users are able to mouse ahead through
severel levels of nested menus without waiting for them to be
displayed.

Display suppression:

With mouse ahead display suppression, a menu is not displayed on the
screen if the user mouses ahead through it quickly enough. 

When the user completely specifies a selection before the computer can 
display the menu, seeing the menu is no longer necessary, if feedback 
is not required, or acting on the selection provides feedback. 
This feature speeds up interaction considerably if the user is fast or
the system is unresponsive. 

Chunking:

Experienced users can learn to "chunk" selection actions into single
gestures they can perform quickly and automatically,
utilizing mouse ahead display suppression more often than novice users.