Multiple Windows
****************

Emacs can split a frame into two or many windows.  Multiple windows can display parts of different buffers, or different parts of one buffer.  Multiple frames always imply multiple windows, because each frame has its own set of windows.  Each window belongs to one and only one frame.

Concepts of Emacs Windows
=========================

Each Emacs window displays one Emacs buffer at any time.  A single buffer may appear in more than one window; if it does, any changes in its text are displayed in all the windows where it appears.  But these windows can show different parts of the buffer, because each window has its own value of point.

At any time, one Emacs window is the selected window; the buffer this window is displaying is the current buffer.  The terminal's cursor shows the location of point in this window.  Each other window has a location of point as well.  On text-only terminals, there is no way to show where those locations are, since the terminal has only one cursor.  On a graphical display, the location of point in a non-selected window is indicated by a hollow box; the cursor in the selected window is blinking or solid.

Commands to move point affect the value of point for the selected Emacs window only.  They do not change the value of point in other Emacs windows, even those showing the same buffer.  The same is true for commands such as C-x b to switch buffers in the selected window; they do not affect other windows at all.  However, there are other commands such as C-x 4 b that select a different window and switch buffers in it.  Also, all commands that display information in a window, including (for example) C-h f (describe-function) and C-x C-b (list-buffers), work by switching buffers in a nonselected window without affecting the selected window.

When multiple windows show the same buffer, they can have different regions, because they can have different values of point.  However, they all have the same value for the mark, because each buffer has only one mark position.

Each window has its own mode line, which displays the buffer name, modification status and major and minor modes of the buffer that is displayed in the window.  The selected window's mode line appears in a different color.  See Mode Line, for full details on the mode line.

Splitting Windows
=================

C-x 2
     Split the selected window into two windows, one above the other (split-window-vertically).

C-x 3
     Split the selected window into two windows positioned side by side (split-window-horizontally).

C-Mouse-2
     In the mode line or scroll bar of a window, split that window.

The command C-x 2 (split-window-vertically) breaks the selected window into two windows, one above the other.  Both windows start out displaying the same buffer, with the same value of point.  By default the two windows each get half the height of the window that was split; a numeric argument specifies how many lines to give to the top window.

C-x 3 (split-window-horizontally) breaks the selected window into two side-by-side windows.  A numeric argument specifies how many columns to give the one on the left.  If you are not using scrollbars, a vertical line separates the two windows. You can customize its color with the face vertical-border. Windows that are not the full width of the screen have mode lines, but they are truncated.  On terminals where Emacs does not support highlighting, truncated mode lines sometimes do not appear in inverse video.

You can split a window horizontally or vertically by clicking C-Mouse-2 in the mode line or the scroll bar.  The line of splitting goes through the place where you click: if you click on the mode line, the new scroll bar goes above the spot; if you click in the scroll bar, the mode line of the split window is side by side with your click.

When a window occupies less than the full width of the frame, it may become too narrow for most of the text lines in its buffer.  If most of its lines are continued (see Continuation Lines), the buffer may become difficult to read.  Therefore, Emacs automatically truncates lines if the window width becomes narrower than 50 columns.  This truncation occurs regardless of the value of the variable truncate-lines (see Line Truncation); it is instead controlled by the variable truncate-partial-width-windows.  If the value of truncate-partial-width-windows is a positive integer (the default is 50), that specifies the minimum width for a partial-width window before automatic line truncation occurs; if the value is nil, automatic line truncation is disabled; and for any other non-nil value, Emacs truncates lines in every partial-width window regardless of its width.

Horizontal scrolling is often used in side-by-side windows. See Horizontal Scrolling.

If split-window-keep-point is non-nil, the default, both of the windows resulting from C-x 2 inherit the value of point from the window that was split.  This means that scrolling is inevitable.  If this variable is nil, then C-x 2 tries to avoid scrolling the text currently visible on the screen, by putting point in each window at a position already visible in the window.  It also selects whichever window contains the screen line that the cursor was previously on.  Some users prefer that mode on slow terminals.

Using Other Windows
===================

C-x o
     Select another window (other-window).  That is o, not zero.

C-M-v
     Scroll the next window (scroll-other-window).

M-x compare-windows
     Find next place where the text in the selected window does not match the text in the next window.

Mouse-1
     Mouse-1, in a window's mode line, selects that window but does not move point in it (mouse-select-window).

To select a different window, click with Mouse-1 on its mode line.  With the keyboard, you can switch windows by typing C-x o (other-window).  That is an o, for ``other,'' not a zero. When there are more than two windows, this command moves through all the windows in a cyclic order, generally top to bottom and left to right. After the rightmost and bottommost window, it goes back to the one at the upper left corner.  A numeric argument means to move several steps in the cyclic order of windows.  A negative argument moves around the cycle in the opposite order.  When the minibuffer is active, the minibuffer is the last window in the cycle; you can switch from the minibuffer window to one of the other windows, and later switch back and finish supplying the minibuffer argument that is requested. See Minibuffer Edit.

The usual scrolling commands (see Display) apply to the selected window only, but there is one command to scroll the next window. C-M-v (scroll-other-window) scrolls the window that C-x o would select.  It takes arguments, positive and negative, like C-v.  (In the minibuffer, C-M-v scrolls the window that contains the minibuffer help display, if any, rather than the next window in the standard cyclic order.)

The command M-x compare-windows lets you compare two files or buffers visible in two windows, by moving through them to the next mismatch.  See Comparing Files, for details.

If you set mouse-autoselect-window to a non-nil value, moving the mouse into a different window selects that window.  This feature is off by default.

Displaying in Another Window
============================

C-x 4 is a prefix key for a variety of commands that switch to a buffer in a different window---either another existing window, or a new window created by splitting the selected window.  See Window Choice, for how Emacs picks or creates the window to use.

C-x 4 b BUFNAME RET
     Select buffer BUFNAME in another window (switch-to-buffer-other-window).

C-x 4 C-o BUFNAME RET
     Display buffer BUFNAME in some window, without trying to select it (display-buffer).  See Displaying Buffers, for details about how the window is chosen.

C-x 4 f FILENAME RET
     Visit file FILENAME and select its buffer in another window (find-file-other-window).  See Visiting.

C-x 4 d DIRECTORY RET
     Select a Dired buffer for directory DIRECTORY in another window (dired-other-window).  See Dired.

C-x 4 m
     Start composing a mail message, similar to C-x m (see Sending Mail), but in another window (mail-other-window).

C-x 4 .
     Find a tag in the current tags table, similar to M-. (see Tags), but in another window (find-tag-other-window).

C-x 4 r FILENAME RET
     Visit file FILENAME read-only, and select its buffer in another window (find-file-read-only-other-window).  See Visiting.

Deleting and Rearranging Windows
================================

C-x 0
     Delete the selected window (delete-window).  The last character in this key sequence is a zero.

C-x 1
     Delete all windows in the selected frame except the selected window (delete-other-windows).

C-x 4 0
     Delete the selected window and kill the buffer that was showing in it (kill-buffer-and-window).  The last character in this key sequence is a zero.

C-x ^
     Make selected window taller (enlarge-window).

C-x }
     Make selected window wider (enlarge-window-horizontally).

C-x {
     Make selected window narrower (shrink-window-horizontally).

C-x -
     Shrink this window if its buffer doesn't need so many lines (shrink-window-if-larger-than-buffer).

C-x +
     Make all windows the same height (balance-windows).

To delete a window, type C-x 0 (delete-window).  (That is a zero.)  The space occupied by the deleted window is given to an adjacent window (but not the minibuffer window, even if that is active at the time).  Once a window is deleted, its attributes are forgotten; only restoring a window configuration can bring it back.  Deleting the window has no effect on the buffer it used to display; the buffer continues to exist, and you can select it in any window with C-x b.

C-x 4 0 (kill-buffer-and-window) is a stronger command than C-x 0; it kills the current buffer and then deletes the selected window.

C-x 1 (delete-other-windows) is more powerful in a different way; it deletes all the windows except the selected one (and the minibuffer); the selected window expands to use the whole frame except for the echo area.

To readjust the division of space among vertically adjacent windows, use C-x ^ (enlarge-window).  It makes the currently selected window one line bigger, or as many lines as is specified with a numeric argument.  With a negative argument, it makes the selected window smaller.  C-x } (enlarge-window-horizontally) makes the selected window wider by the specified number of columns.  C-x { (shrink-window-horizontally) makes the selected window narrower by the specified number of columns.

When you make a window bigger, the space comes from its peers.  If this makes any window too small, it is deleted and its space is given to an adjacent window.  The minimum size is specified by the variables window-min-height and window-min-width.

C-x - (shrink-window-if-larger-than-buffer) reduces the height of the selected window, if it is taller than necessary to show the whole text of the buffer it is displaying.  It gives the extra lines to other windows in the frame.

You can also use C-x + (balance-windows) to even out the heights of all the windows in the selected frame.

Mouse clicks on the mode line provide another way to change window heights and to delete windows.  See Mode Line Mouse.

Displaying a Buffer in a Window
===============================

It is a common Emacs operation to display or ``pop up'' some buffer in response to a user command.  There are several different ways by which commands do this.

Many commands, like C-x C-f (find-file), display the buffer by ``taking over'' the selected window, expecting that the user's attention will be diverted to that buffer.  These commands usually work by calling switch-to-buffer internally (see Select Buffer).

Some commands try to display ``intelligently'', trying not to take over the selected window, e.g. by splitting the selected window and displaying the desired buffer in the child window.  Such commands, which include the various help commands (see Help), work by calling display-buffer internally.  See Window Choice, for details.

Other commands do the same as display-buffer, and additionally select the displaying window so that you can begin editing its buffer.  The command C-x ` (next-error) is one example (see Compilation Mode).  Such commands work by calling pop-to-buffer internally.  See Displaying Buffers in Windows (The Emacs Lisp Reference Manual).

Commands with names ending in -other-window behave like display-buffer, except that they never display in the selected window.  Several of these commands are bound in the C-x 4 prefix key (see Pop Up Window).

Commands with names ending in -other-frame behave like display-buffer, except that they (i) never display in the selected window and (ii) prefer to create a new frame to display the desired buffer instead of splitting a window---as though the variable pop-up-frames is set to t (see Window Choice). Several of these commands are bound in the C-x 5 prefix key.

How display-buffer works
------------------------

The display-buffer command (as well as commands that call it internally) chooses a window to display using the following steps:

  * First, check if the buffer should be displayed in the selected window regardless of other considerations.  You can tell Emacs to do this by adding the desired buffer's name to the list same-window-buffer-names, or adding a matching regular expression to the list same-window-regexps.  By default, these variables are nil, so this step is skipped.

  * Otherwise, if the buffer is already displayed in an existing window, ``reuse'' that window.  Normally, only windows on the selected frame are considered, but windows on other frames are also reusable if you change display-buffer-reuse-frames to t, or if you change pop-up-frames (see below) to t.

  * Otherwise, if you specified that the buffer should be displayed in a special frame by customizing special-display-buffer-names or special-display-regexps, do so.  See Special Buffer Frames.

  * Otherwise, optionally create a new frame and display the buffer there. By default, this step is skipped.  To enable it, change the variable pop-up-frames to a non-nil value.  The special value graphic-only means to do this only on graphical displays.

  * Otherwise, try to create a new window by splitting the selected window, and display the buffer in that new window.

     The split can be either vertical or horizontal, depending on the variables split-height-threshold and split-width-threshold.  These variables should have integer values.  If split-height-threshold is smaller than the selected window's height, the split puts the new window below.  Otherwise, if split-width-threshold is smaller than the window's width, the split puts the new window on the right.  If neither condition holds, Emacs tries to split so that the new window is below---but only if the window was not split before (to avoid excessive splitting).

  * Otherwise, display the buffer in an existing window on the selected frame.

  * If all the above methods fail for whatever reason, create a new frame and display the buffer there.

Window Handling Convenience Features and Customization
======================================================

M-x winner-mode is a global minor mode that records the changes in the window configuration (i.e. how the frames are partitioned into windows), so that you can ``undo'' them.  To undo, use C-c left (winner-undo).  If you change your mind while undoing, you can redo the changes you had undone using C-c right (M-x winner-redo).  Another way to enable Winner mode is by customizing the variable winner-mode.

The Windmove commands move directionally between neighboring windows in a frame.  M-x windmove-right selects the window immediately to the right of the currently selected one, and similarly for the ``left,'' ``up,'' and ``down'' counterparts.  M-x windmove-default-keybindings binds these commands to S-right etc.  (Not all terminals support shifted arrow keys, however.)

Follow minor mode (M-x follow-mode) synchronizes several windows on the same buffer so that they always display adjacent sections of that buffer.  See Follow Mode.

M-x scroll-all-mode provides commands to scroll all visible windows together.  You can also turn it on by customizing the variable scroll-all-mode.  The commands provided are M-x scroll-all-scroll-down-all, M-x scroll-all-page-down-all and their corresponding ``up'' equivalents.  To make this mode useful, you should bind these commands to appropriate keys.