On a non-windowing display, Ediff sets things up in one frame, splitting it between a small control window and the windows for buffers A, B, and C. The split between these windows can be horizontal or vertical, which can be changed interactively by typing | while the cursor is in the control window.
On a window display, Ediff sets up a dedicated frame for Ediff Control
Panel and then it chooses windows as follows: If one of the buffers
is invisible, it is displayed in the currently selected frame. If
a buffer is visible, it is displayed in the frame where it is visible.
If, according to the above criteria, the two buffers fall into the same
frame, then so be it—the frame will be shared by the two. The same
algorithm works when you type C-l (
The above behavior also depends on whether the current frame is splittable, dedicated, etc. Unfortunately, the margin of this book is too narrow to present the details of this remarkable algorithm.
The upshot of all this is that you can compare buffers in one frame or in different frames. The former is done by default, while the latter can be achieved by arranging buffers A, B (and C, if applicable) to be seen in different frames. Ediff respects these arrangements, automatically adapting itself to the multi-frame mode.
Ediff uses the following variables to set up its control panel (a.k.a. “control buffer”, a.k.a. “quick help window”):
ediff-control-frame-parametersdirectly. For instance, you can specify in ~/.Xdefaults the color of the control frame using the resource ‘Ediff*background’.
In general, any X resource pertaining the control frame can be reached
via the prefix
ediff-control-frame-position-functionto an appropriate function. The default value of this variable is
ediff-make-frame-position. This function places the control frame in the vicinity of the North-East corner of the frame displaying buffer A.
The following variables can be used to adjust the location produced by
ediff-make-frame-position and for related customization.
t, the control frame becomes iconified automatically when you toggle the quick help message off. This saves valuable real estate on the screen. Toggling help back will deiconify the control frame.
To start Ediff with an iconified Control Panel, you should set this
nil (see Quick Help Customization). This behavior is useful
only if icons are allowed to accept keyboard input (which depends on the
window manager and other factors).
To make more creative changes in the way Ediff sets up windows, you can
rewrite the function
ediff-setup-windows. However, we believe
that detaching Ediff Control Panel from the rest and making it into a
separate frame offers an important opportunity by allowing you to
iconify that frame. The icon will usually accept all of the Ediff
commands, but will free up valuable real estate on your screen (this may
depend on your window manager, though).
The following variable controls how windows are set up:
ediff-setup-windows-multiframefunction, which is the default on windowing displays. The plain setup, one where all windows are always in one frame, is done by
ediff-setup-windows-plain, which is the default on a non-windowing display (or in an xterm window). In fact, under Emacs, you can switch freely between these two setups by executing the command
ediff-toggle-multiframeusing the Minibuffer of the Menubar. If you don't like any of these setups, write your own function. See the documentation for
ediff-window-setup-functionfor the basic guidelines. However, writing window setups is not easy, so you should first take a close look at
You can run multiple Ediff sessions at once, by invoking Ediff several times without exiting previous Ediff sessions. Different sessions may even operate on the same pair of files.
Each session has its own Ediff Control Panel and all the regarding a particular session is local to the associated control panel buffer. You can switch between sessions by suspending one session and then switching to another control panel. (Different control panel buffers are distinguished by a numerical suffix, e.g., ‘Ediff Control Panel<3>’.)