Focus (computing)
From Wikipedia, the free encyclopedia
In computing, the focus indicates the component of the graphical user interface which is currently selected. Text entered at the keyboard or pasted from a clipboard is sent to the component which currently has the focus.
The concept is similar to a cursor in a text-based environment. However, when considering a graphical interface, there is also a mouse cursor involved. Moving the mouse will typically move the mouse cursor without changing the focus. The focus can usually be changed by clicking on a component that can receive focus with the mouse. Many desktops also allow the focus to be changed with the keyboard. By convention, the tab key is used to move the focus to the next focusable component and shift + tab to the previous one. This feature was designed to make it easier for people that have a hard time using a mouse to use the user interface. In certain circumstances, the arrow keys can also be used to move focus.
[edit] Window focus
The behaviour of focus on one's desktop can be governed by policies in window management. On most mainstream user-interfaces, such as ones made by Microsoft and Apple Computer, it is common to find a "focus follows click" policy (or "click to focus"), where one must click the mouse inside of the window for that window to gain focus. This also typically results in the window being raised above all other windows on screen.
Another common policy on UNIX systems using X11 is the "focus follows mouse" policy, where the focus automatically follows the current placement of the mouse. One consequence of this policy is that no window has focus when the mouse is moved over the background with no window underneath. Thus a variant of this policy is "sloppy focus", where focus remains on the last focused window when the mouse is moved over the empty background.
The most effective policy is a subject of much debate. For new and inexperienced computer users, "focus follows mouse" could lead to easy confusion when inadvertently moving the mouse. However for more experienced users it allows greater control, especially when combined with the policy of not raising windows. For example, text can be copied from a large background window into a small foreground window (e.g a web browser or an instant messaging client) without rearranging windows (e.g using Alt+Tab to switch active windows).
[edit] Intra-window component focus
Individual components may also have a cursor position. For instance in a text editing package, the text editing window must have the Focus so that text can be entered. When text is entered into the component, it will appear at the position of the text-cursor, which will also normally be moveable using the mouse cursor.
Which component that should have the default focus and how focus should move between components is a difficult but important problem in user interface design. Giving the wrong thing focus means that the user has to waste time moving the focus. Conversively, giving the right thing focus can significantly enhance the users experience.
