Input Focus

At any time, one frame in Emacs is the selected frame. The selected window always resides on the selected frame.

Function: selected-frame

This function returns the selected frame.

The X server normally directs keyboard input to the X window that the mouse is in. Some window managers use mouse clicks or keyboard events to shift the focus to various X windows, overriding the normal behavior of the server.

Lisp programs can switch frames "temporarily" by calling the function select-frame. This does not override the window manager; rather, it escapes from the window manager's control until that control is somehow reasserted.

When using a text-only terminal, there is no window manager; therefore, switch-frame is the only way to switch frames, and the effect lasts until overridden by a subsequent call to switch-frame. Only the selected terminal frame is actually displayed on the terminal. Each terminal screen except for the initial one has a number, and the number of the selected frame appears in the mode line after the word `Emacs' (see section Variables Used in the Mode Line).

Function: select-frame frame

This function selects frame frame, temporarily disregarding the focus of the X server if any. The selection of frame lasts until the next time the user does something to select a different frame, or until the next time this function is called.

Emacs cooperates with the X server and the window managers by arranging to select frames according to what the server and window manager ask for. It does so by generating a special kind of input event, called a focus event. The command loop handles a focus event by calling handle-switch-frame. See section Focus Events.

Command: handle-switch-frame frame

This function handles a focus event by selecting frame frame.

Focus events normally do their job by invoking this command. Don't call it for any other reason.

Function: redirect-frame-focus frame focus-frame

This function redirects focus from frame to focus-frame. This means that focus-frame will receive subsequent keystrokes intended for frame. After such an event, the value of last-event-frame will be focus-frame. Also, switch-frame events specifying frame will instead select focus-frame.

If focus-frame is nil, that cancels any existing redirection for frame, which therefore once again receives its own events.

One use of focus redirection is for frames that don't have minibuffers. These frames use minibuffers on other frames. Activating a minibuffer on another frame redirects focus to that frame. This puts the focus on the minibuffer's frame, where it belongs, even though the mouse remains in the frame that activated the minibuffer.

Selecting a frame can also change focus redirections. Selecting frame bar, when foo had been selected, changes any redirections pointing to foo so that they point to bar instead. This allows focus redirection to work properly when the user switches from one frame to another using select-window.

This means that a frame whose focus is redirected to itself is treated differently from a frame whose focus is not redirected. select-frame affects the former but not the latter.

The redirection lasts until redirect-frame-focus is called to change it.

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