Applications of Mouse

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Usually, the mouse is used to control the motion of a cursor in two dimensions in a graphical user interface. Files, programs or actions can be selected from a list of names, or in graphical interfaces through pictures called "icons" and other elements. For example, a text file might be represented by a picture of a paper notebook, and clicking while the pointer hovers this icon might cause a text editing program to open the file in a window. (See also point-and-click)
Mice can also be used gesturally; that is, a stylized motion of the mouse cursor itself, called gesture, can be used as a form of command and mapped to a specific 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 finer motor control from the user. However, a few gestural conventions have become widespread, including the drag-and-drop gesture, in which:

1. The user presses the mouse button while the mouse cursor is over an interface object
2. Moves the cursor to a different location while holding the button down
3. Releases the mouse button

For example, a user might drag and drop a picture representing a file 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 primary (leftmost in a right-handed configuration) button on the mouse will select items, and the secondary (rightmost in a right-handed) 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 primary button click, will bring up a contextual menu of alternative actions for that link in response to a secondary-button click, and will often open the link in a new tab or window in response to a click with the tertiary (middle) mouse button.

One, two or three mouse buttons?

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 until late 2005, Apple shipped computers with a single-button mouse, whereas most other platforms used a multi-button mouse. Apple and its advocates argued that single-button mice are more efficient, and that multi-button mice are confusing for novice users. The Macintosh user interface is designed so that all functions are available with a single button mouse. Apple's Human Interface Guidelines still specify that all functions need to be available with a single button mouse. However, X Window System applications, which Mac OS X can also run, were designed with the use of two or even three button mice in mind, causing even simple operations like "cut and paste" to become awkward. Mac OS X natively supports multi-button mice, so many users of older Macintoshes choose to use third-party mice on their machines. On August 2, 2005, Apple introduced their Mighty Mouse multi-button mouse, which has four independently programmable buttons and a "scroll ball" which can be used to scroll in any direction. This is now the mouse supplied with all new Macintosh computers.
Advocates of multiple-button mice point out that support for a single button mouse often leads to clumsy workarounds in interfaces where more than one action may be useful for a given object. There are several common workarounds, and even widely used Macintosh software packages that otherwise fully conform to the Human Interface Guidelines, including web browsers and graphics editing programs, occasionally require the use of one of them. One such workaround is the press-and-hold technique. In a press-and-hold, the user presses and holds the single button, and after a certain period, the button press is not perceived as a single click but as a separate action. This has two drawbacks: first, 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, otherwise their press might be interpreted as a single click. 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.
Alternatively, the user may be required to hold down a key on the keyboard while pressing the button (otherwise known as mouse chording - Macintosh computers use the ctrl key). This has the disadvantage that it requires that both the user's hands be engaged. It also requires that the user perform two actions on completely separate devices in concert; that is, pressing a key on the keyboard while pressing a button on the mouse. This can be a very daunting task for a disabled user. Studies have found all of the above workarounds less usable than additional mouse buttons for experienced users. Most machines running Unix or a Unix-like operating system run the X Window System which almost always requires a three button mouse. In X, the buttons are numbered by convention. This allows user instructions to apply to mice or pointing devices that do not use conventional button placement. For example, a left handed user may reverse the buttons, usually with a software setting. With non-conventional button placement, user directions that say "left mouse button" or "right mouse button" are confusing. The ground-breaking Xerox Parc Alto and Dorado computers from the mid-1970s used three-button mice, and each button was assigned a color. Red was used for the left (or primary) button, yellow for the middle (secondary), and blue for the right (meta or tertiary). This naming convention lives on in some SmallTalk environments, such as Squeak, and can be less confusing than the right, middle and left designations.