Pointer (graphical user interfaces)
In computing, a pointer or mouse cursor (as part of a personal computer WIMP style of interaction) is a graphical image on the computer monitor or other display device. The pointer echoes movements of the pointing device, commonly a mouse or touchpad, and signals the point where actions of the user take place. It can be used to select and move other graphical user interface elements, and is distinct from the cursor, which responds to keyboard input. The cursor may also be repositioned using the pointer.
The pointer commonly appears as an angled arrow, (angled because historically that improved appearance on low resolution screens ) but it can vary within different programs or operating systems. The use of a pointer is employed when the input method, or pointing device, is a device that can move fluidly across a screen and select or highlight objects on the screen. In GUIs where the input method relies on hard keys, such as the five-way key on many mobile phones, there is no pointer employed, and instead the GUI relies on a clear focus state.
The pointer "hotspot" is the active pixel of the pointer, used to target a click. The hotspot is normally along the pointer edges or in its center, though it may reside at any location in the pointer.
In many GUIs, moving the pointer around the screen may reveal other screen hotspots as the pointer changes shape depending on the circumstances. For example:
- In text that the user can select or edit, the pointer changes to a vertical bar with little cross-bars (or curved serif-like extensions) at the top and bottom — sometimes called an "I-beam" since it resembles the cross-section of the construction detail of the same name.
- When displaying a document, the pointer can appear as a hand with all fingers extended allowing scrolling by "pushing" the displayed page around.
- Graphics-editing pointers such as brushes, pencils or paint buckets may display when the user edits an image.
- On an edge or corner of a window the pointer usually changes into a double arrow (horizontal, vertical, or diagonal) indicating that the user can drag the edge/corner in an indicated direction in order to adjust the size and shape of the window.
- The corners and edges of the whole screen may also act as hotspots. According to Fitts's law, which predicts the time it takes to reach a target area, moving mouse and trackball pointers to those spots is easy and fast. As the pointer usually stops when reaching a screen edge, the size of those spots can be considered of virtual infinite size, so the hot corners and edges can be reached quickly by throwing the pointer toward the edges.
- While a computer process is performing tasks and cannot accept user input, a wait pointer (an hourglass in Windows before Vista and many other systems, spinning ring in Windows Vista, watch in classic Mac OS, or spinning ball in Mac OS X) is displayed when the mouse pointer is in the corresponding window.
- When the pointer hovers over a hyperlink, a mouseover event changes the pointer into a hand with an outstretched index finger. Often some informative text about the link may pop up in a tooltip, which disappears when the user moves the pointer away. The tooltips revealed in the box depend on the implementation of the web browser; many web browsers will display the "title" of the element, the "alt" attribute, or the non-standard "tooltips" attribute. This pointer shape was first used for hyperlinks in Apple Computer's HyperCard.
- The mouseover or hover gesture can also present information about what the pointer is hovering over; the information is a description of what selecting an active element is for or what it will do, it appears only when stationary over content. A common use of viewing the information is when browsing the internet to know the destination of a link before selecting it, if the URL of the text is not recognisable.
Pointer trails and animation
Pointer trails can be used to enhance its visibility during movement. Pointer trails are a feature of GUI operating systems to enhance the visibility of the pointer. Although disabled by default, pointer trails have been an option in every version of Microsoft Windows since Windows 3.1.
When pointer trails are active and the mouse is moved, the system waits a moment before removing the pointer image from the old location on the screen. A copy of the pointer persists at every point that the pointer has visited in that moment, resulting in a snake-like trail of pointer icons that follow the actual pointer. When the user stops moving the mouse, the trails disappear and the pointer returns to normal.
Introduced with Windows NT, an animated pointer was a small looping animation that was played at the location of the pointer. This is used, for example, to provide a visual cue that the computer is busy with a task. After their introduction, many animated pointers became available for download from third party suppliers. Unfortunately, animated pointers are not without their problems. In addition to imposing a small additional load on the CPU, the animated pointer routines did introduce a security vulnerability. A client-side exploit known as the Windows Animated Cursor Remote Code Execution Vulnerability used a buffer overflow vulnerability to load malicious code via the animated cursor load routine of Windows.
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