Applications of mice in user interfaces
Usually, the mouse is used to control the motion of a cursor in two dimensions in a graphical user interface. Objects, such as files, programs, or actions, are represented visually by pictures called icons and buttons; the mouse cursor can be used to select or activate such items by moving the cursor over the picture and pressing one of the mouse buttons. For example, a text file might be represented by a picture of a piece of notebook paper, and clicking on this icon might cause a text editing program to open the file in a new window. (See also point and click.)
Mice can also be used gesturally---that is, a stylized motion of the mouse cursor itself can be used as a form of input. In a gestural interface, a particular "gesture" (stylized motion) may be mapped to an action: for example, in a drawing program, moving the mouse in a rapid "x" motion over a shape might delete the shape.
Gestural interfaces are rarer, and often harder to use, than plain pointing and clicking, because they require more fine motor control of the user. However, a few gestural conventions have become widespread, including the drag and drop gesture, in which:
- the user presses the mouse button while the mouse cursor is over an object,
- then holds down the button while moving the cursor to a different location,
- and finally releases the mouse button.
This motion is commonly used to move the item from one location to another---the item is "dragged" from its old location and "dropped" in its new one. For example, a user might drag and drop a picture of a file from a folder onto a picture of a trash can, indicating that the file should be deleted.
Other uses of the mouse's input are common in special application domains. In interactive three-dimensional graphics, the mouse's motion is often directly translated into changes in the virtual camera's orientation. For example, in the Quake computer game, the mouse is usually used to control the direction in which the player's "head" faces: moving the mouse up will cause the player to look up, revealing the view above the player's head.
When mice have more than one button, software may assign different functions to each button. Often, the leftmost button on the mouse will select items, and the rightmost button will bring up a menu of alternative actions applicable to that item. For example, on platforms with more than one button, the Mozilla web browser will follow a link in response to a left button click, and will bring up a menu of alternative actions for that link in response to a right button click.
One button or two?
The issue of whether a mouse should have exactly one button or more than one has attracted a surprising amount of controversy. From the first Macintosh onward, Apple always shipped computers with a single-button mouse, whereas most other platforms used a multiple-button mouse. Apple and its advocates claim that single-button mice are more efficient, and that multiple-button mice are confusing for novice users. The original Macintosh user interface was designed so that all functions were available to a single button mouse.
Advocates of multiple-button mice point out that the lack of additional mouse buttons often leads to clumsy workarounds in interfaces where more than one action may be useful for a given object. These workarounds include the following:
- double-click
- A "double-click" is when the user presses the button twice in quick succession. This is mapped to a separate action than a single click. For example, in the original Macintosh Finder, the user single-clicked to select a file, and double-clicked in order to open that file. Usability studies have found that the double-click is confusing and hard to use---for example, users with poor motor skills may not perform the second click fast enough, so that the action is interpreted as two single clicks rather than a double click. However, virtually all modern interfaces require the user to double click even if he or she has a two-button mouse, eliminating any advantage, if the option for general conversion to single click mode is not enabled.
- press-and-hold
- In a "press-and-hold", the user presses and hold the single button, and after a certain period, the button press is not perceived as a single click but as a separate action. On Macintosh platforms, Netscape used press-and-hold to substitute for a second mouse button. This has two drawbacks: first, as with double-clicking, a slow user may press-and-hold inadvertently. Second, the user must wait while the software detects that the click is actually a press-and-hold. Furthermore, the remedies for these two drawbacks conflict with each other: the longer the lag time, the more the user must wait; and the shorter the lag time, the more likely it is that some user will accidentally press-and-hold when meaning to click.
- key-and-click
- Finally, the user may be required to hold down a key on the keyboard while pressing the button. This has the disadvantage that it requires that both the user's hands be engaged. It also requires that the user do two actions on completely separate devices in concert: pressing a key on the keyboard while pressing a button on the mouse.
Studies have found all of the above less usable than additional mouse buttons for experienced users. Today, many widely used Apple software packages, including web browsers and graphics editing programs, use one or more of the above workarounds. Critics of single-button mice point to these facts as evidence that mice should have more than one button.
See also
