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With long files, I like to have two buffers that display the same file but at different positions. However, since I have two physical displays, I'd like to have two Emacs buffer, each on its own monitor, and then I could open 3, or even 4 copies of the same file! In theory...

In practice, when I try C-x 5 b or C-x 5 f, instead of opening the file / creating a new buffer with the same content in another frame, the focus goes back into original frame, original buffer...

Any thoughts?

OK, I now realized that I can create a new frame, which will then automatically show the currently selected buffer: M-xnew-frame. But what about existing frames?

wvxvw
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    I use a custom function with the `display-buffer-alist` to display buffers in select frames and select windows within those frames. For an example of how this works, check out the answer in this related thread entitled "*How to intercept a file before it opens and decide which frame*": https://stackoverflow.com/questions/18346785/how-to-intercept-a-file-before-it-opens-and-decide-which-frame As you may already know, the `buffer-list` for each frame cannot be relied upon as a method for associating buffers with a frame. You may be interested in `frame-bufs` by Alp Aker to associate buffers. – lawlist Apr 04 '18 at 14:04
  • @lawlist thank you, I'm reading about this. – wvxvw Apr 04 '18 at 14:21
  • You may also want to look at this question: https://superuser.com/questions/338140/edit-one-file-in-two-different-buffers-in-emacs – quazgar Nov 27 '20 at 07:51

6 Answers6

6

Three different things come to mind, depending on just what you want. Perhaps one or more of them will help.

  1. C-x 5 2 (new frame for the current buffer).

  2. C-x 3 (or C-x 2), followed by M-x follow-mode <RET>. But that shows the buffer in separate windows, not separate frames.

  3. Indirect buffers. Each such buffer can be dedicated to a different part of the same buffer (and those parts can overlap). See Narrow Indirect (library narrow-indirect.el).

memtha
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Drew
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3

You can you C-x <LEFT> and C-x <RIGHT> to cycle among all open buffers in the current window.

It's not perfect, but it's the only way I've found to change the buffer in an existing frame to one that's open in another frame.

Stanley Bak
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1

Have you tried C-x 5 2? It is make-frame-command that should do what you want as far as I understand.

For my needs I have created similar function to make new frame with current buffer having the same frame-width and frame-height:

(defun haba/make-new-frame ()
    (interactive)
    (make-frame `((width . ,(frame-width)) (height . ,(frame-height)))))

PS Or maybe you want smth else? Maybe you want to duplicate current frame with all windows opened there? I have read your question 4 times... :)

PS2

What I think happens

  1. You open a new frame with C-x 5 b
  2. Then you want to open another buffer in that frame and again use C-x 5 b

By default C-x 5 b will search for a buffer in list of displayed buffers in all frames and will switch to it in another existing frame instead of creating a new one.

Just use regular C-x b in a new frame:

  1. C-x 5 2 to open current buffer in a new frame
  2. C-x b to open any buffer in selected frame (in your case you are in a new frame)
Maxim Kim
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    Sorry, after asking the initial question, I realized that I can partially solve it by creating new frame with displaying the buffer I need, but if I already have one frame open, I cannot display an already existing buffer in it. – wvxvw Apr 04 '18 at 14:20
  • Still don't get it. If I open file, for example `init.el` then press `C-x 5 2` and `C-x 5 2` I get 3 frames opened with the same buffer `init.el`. – Maxim Kim Apr 04 '18 at 14:24
  • Still don't get it, part 2. If I open `init.el` then press `C-x 5 2` and there `C-x C-f` and select file `blabla.txt` I will have `init.el` in one frame and `blabla.txt` in another. – Maxim Kim Apr 04 '18 at 14:27
  • @wvxvw Still don't get it, part 3. MAYBE, in a new frame you try to open buffer/file with FRAME commands (`C-x 5 b`). In that situation, you will be redirected to the frame that has selected buffer visible (default behaviour as far as I remember) – Maxim Kim Apr 04 '18 at 14:29
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    OK, here's the scenario: I open `init.el` using `C-x 5 2` in a new frame. Then in the new frame I open a different file, say. `.netrc`, then I switch to the first frame (say, by pressing `M-TAB`), and then try to display `.netrc` in that frame. The desired effect is that `.netrc` is displayed in both frames, the actual effect is that the second frame gets focused and displays `.netrc`, while the first frame still displays `init.el`. – wvxvw Apr 05 '18 at 10:21
  • And how do you "try to display `.netrc` in that frame"? With general `C-x b` or frame `C-x 5 b`? – Maxim Kim Apr 05 '18 at 11:11
1

Here is an example using the display-buffer family of functions, based upon a more complicated example: https://stackoverflow.com/questions/18346785/how-to-intercept-a-file-before-it-opens-and-decide-which-frame . As stated in that related thread, there are several different ways to do this, including, but not limited to let-binding the display-buffer-alist. In this example, we just use the function my-frame-fn in the second argument to display-buffer. We can of course get fancy by examining all of the frame names and add a consecutive numeric digit to the frame name; or, not change the frame name at all; or ... the sky is the limit. We can also add additional frame parameters to place the top / left coordinates wherever we want. We can also adjust the frame size upon frame creation including pixelwise (https://emacs.stackexchange.com/a/17354/2287), or after the fact (https://www.gnu.org/software/emacs/manual/html_node/elisp/Size-and-Position.html). And, we could always programmatically set/select the original frame/buffer instead of the new one if we wanted to ....

I do not like to use select-frame-set-input-focus in my setup because it will cause frames on OSX to acquire focus and steal away focus from another program that I might be using; e.g., in the case of a long running Emacs function. So, instead I use the combination of select-frame and raise-frame. Please feel free to substitute select-frame for select-frame-set-input-focus and remove raise-frame if that is needed for your OS or you simply prefer it like that.

USAGE (1 of 2):  (display-buffer (current-buffer) '(my-frame-fn))

USAGE (2 of 2):  (display-buffer (find-file-noselect FILENAME) '(my-frame-fn))

(defun my-frame-fn (buffer alist)
"Display the incoming BUFFER in a frame that does not already display it.
Use up the existing frames first, before deciding to create a new frame."
  (let (target-frame)
    (catch 'break
      (dolist (the-frame (frame-list))
        (when (not (get-buffer-window buffer the-frame))
          (throw 'break
            (progn
              (setq target-frame the-frame)
              (modify-frame-parameters the-frame
                (list (cons 'name "OLD"))))))))
    (when (null target-frame)
      (setq target-frame (make-frame (list (cons 'name "NEW")))))
    (select-frame target-frame 'norecord)
    (set-window-buffer (get-largest-window) buffer)
    (select-window (get-buffer-window buffer))
    (raise-frame target-frame)))
lawlist
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1

Try this:

Pressing C-x 4 c (edit: thanks to @krupan, C-x 4 c stands for M-x clone-indirect-buffer) in a buffer e.g. myFile.txt creates a new indirect buffer and opens it in a window with the same contents and appends <2> to the filename as new buffer name, e.g. myFile.txt<2>

Go to the window with e.g. myFile.txt<2> and create a new frame with C-x 5 2. The indirect buffer should be displayed in the new frame. Now you can go back to the first frame and close the window and you have the desired result.

You can edit and navigate the new indirect buffer as if it is another file, all changes are saved to the original file. You can even rename the indirect buffer for easier navigation between buffers: M-x rename-buffer or simply create the new indirect buffer with C-u C-x 4 c and specify a name.

GNUmon
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0

It looks like you can M-x clone-indirect-buffer and then open the clone in the other frame. I haven't played with this a lot yet, but so far so good.

krupan
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