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Mouse keys is a feature of some graphical user interfaces that uses the keyboard (especially numeric keypad) as a pointing device (usually replacing a mouse). Its roots lie in the earliest days of visual editors when line and column navigation was controlled with arrow keys (e.g., hjkl, ctl-esdx). Today, mouse keys usually refers to the numeric keypad layout standardized with the introduction of the X Window System in 1984.

Layout

X window system MouseKeys default numpad layout

key	action
Num Lock	With Alt-Shift Enable/Disable MouseKeys
8	cursor up
2	cursor down
6	cursor right
4	cursor left
7	cursor up and left
9	cursor up and right
3	cursor down and right
1	cursor down and left
/	select primary button
*	select modifier button
-	select alternate button
5	click selected button
+	double click selected button
0	depress selected button
.	release selected button
Enter	Enter Key

History

Historically, MouseKeys supported GUI programs when many terminals had no dedicated pointing device. As pointing devices became ubiquitous, the use of mouse keys narrowed to situations where a pointing device was missing, unusable, or inconvenient. Such situations may arise from the following:

• precision requirements (e.g., technical drawing)
• disabled user or ergonomics issues
• environmental limits (e.g., vibration in car or plane)
• broken equipment

MouseKeysAccel

X window system MouseKeysAccel trajectory

parameter	meaning
mk_delay	milliseconds between the initial key press and first repeated motion event
mk_interval	milliseconds between repeated motion events
mk_max_speed	steady speed (in action_delta units) applied each event
mk_time_to_max	number of events (count) accelerating to steady speed
mk_curve	ramp used to reach maximum pointer speed

The X Window System MouseKeysAccel control applies action (usually cursor movement) repeatedly while a direction key {1,2,3,4,6,7,8,9} remains depressed. When the key is depressed, an action_delta is immediately applied. If the key remains depressed, longer than mk_delay milliseconds, some action is applied every mk_interval milliseconds until the key is released. If the key remains depressed, after more than mk_time_to_max actions have been applied, action_delta magnified mk_max_speed times, is applied every mk_interval milliseconds.

The first mk_time_to_max actions increase smoothly according to an exponential.

$\mathrm {action\_delta} \times \mathrm {mk\_max\_speed} \times \left({\frac {i}{\mathrm {mk\_time\_to\_max} }}\right)^{\frac {1000+\mathrm {mk\_curve} }{1000}}$

mk_curve	result
-1000	uniform speed, linearly increasing action
0	uniform acceleration, linearly increasing speed
1000	uniform jerk, linearly increasing acceleration

These five parameters are configurable.

Enabling

Under the X Window Systems Xorg and XFree86 used on Unix-like systems such as Linux, BSD, and AIX, MouseKeys (and MouseKeysAccel) is nominally (de)activated by Alt+Shift+Num Lock. MouseKeys without acceleration (also known as plot mode) is sometimes available with Shift+NumLock. This is independent of the Window Manager in use and may be overridden by a configuration file. There are also various utilities to allow more precise control via user-configurable key bindings, such as xmousekeys and xdotool.

MouseKeys for Apple Inc's Mac OS X is enabled and configured via the Accessibility ([apple] => System Preferences => Accessibility => Mouse & Trackpad).

Microsoft changed the method of enabling between Windows 2000, Windows XP (added diagonal cursor movement and MouseKeysAccel), and Windows Vista.

See also

• FilterKeys feature
• StickyKeys feature
• Togglekeys feature
• On-screen keyboard

References

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