scroll-other-window for non-emacs windows

[tarustdev]

Hello!

Is it possible to scroll non-emacs window (Chromium browser for example) when emacs window is active?

With 2 emacs windows opened I can scroll other (non-active) window with commands scroll-other-window and scroll-other-window-down.

I added next code to exwm-input-global-keys and now I can scroll non-active emacs window when non-emacs window is active (for example scroll non-active text buffer when Chromium is active).

([?\C-\M-v] . scroll-other-window)
([?\C-\M-\S-v] . scroll-other-window-down)

Also I added next code to exwm-input-simulation-keys and now i can scroll non-emacs window when it is active.

([?\M-v] . [prior])
([?\C-v] . [next])

But this setup doesn't work for scrolling non-active non-emacs windows (Always getting "Beginning of buffer" or "End of buffer" even if this window scrolling correctly when it is active). Am I doing something wrong or are there any limitations for desired behavior?

Thanks!

[medranocalvo]

Hello @tarustdev,

as you see, supporting scroll-other-window from an X window can be made by passing those key events to the underlying exwm-mode buffer. That's what exwm-input-global-keys does. Mapping M-v and C-v to PageUp and PageDown in the X window can be done with exwm-input-simulation-keys. That might be intuitive for you. The missing part, scrolling the X window from an Emacs buffer, is not supported at the moment, but can be implemented as follows:

(defun medranocalvo-exwm-scroll-up-command (&optional arg)
  (interactive "^P")
  (cond
   ((eq arg '-)
    (medranocalvo-exwm-scroll-down-command nil))
   ((< (prefix-numeric-value arg) 0)
    (medranocalvo-exwm-scroll-down-command (- (prefix-numeric-value arg))))
   (t
    (exwm-input--fake-key (pcase exwm-class-name
                            ("XTerm" 'S-next)
                            (t 'next))))))

(defun medranocalvo-exwm-scroll-down-command (&optional arg)
  (interactive "^P")
  (cond
   ((eq arg '-)
    (medranocalvo-exwm-scroll-up-command nil))
   ((< (prefix-numeric-value arg) 0)
    (medranocalvo-exwm-scroll-up-command (- (prefix-numeric-value arg))))
   (t
    (exwm-input--fake-key (pcase exwm-class-name
                            ("XTerm" 'S-prior)
                            (t 'prior))))))

(keymap-set exwm-mode-map "<remap> <scroll-up-command>" #'medranocalvo-exwm-scroll-up-command)
(keymap-set exwm-mode-map "<remap> <scroll-down-command>" #'medranocalvo-exwm-scroll-down-command)

With the code above I was able to scroll an XTerm window (after enabling "Allow SendEvents"; via XTerm's C- menu).

I wonder whether this functionality should be provided by EXWM by default. For me, EXWM extends Emacs concepts to X windows, so scroll-other-window should indeed apply to X windows as well. What do others think about it? If that's something we'd like to do, we have to think how to deal with different applications using different keys for scrolling (for example XTerm above). Additionally, we should collect all such missing functions to ensure the mechanism is valid for all of them. I could quickly find beginning-of-buffer-other-window and end-of-buffer-other-window, which are similar to the scrolling commands but, are there other Emacs commands that control other windows applicable to X windows?

Another issue I'm wondering about is whether we should export the internal function exwm-input--fake-key and, if so, whether the current API is good.

[tarustdev]

@medranocalvo thanks a lot for the explanation and implementation example! It works correctly in my case.

[medranocalvo]

You are welcome.

I would appreciate input on the thoughts above (from everyone):

• Should we implement scroll-other-window support in EXWM?
• How can we deal with different applications using different keys? Can we reuse exwm-input-simulation-keys somehow? Seems hacky. Should we ask users to remap scroll-up-command buffer-locally in the exwm-mode buffer of those applications? Seems cumbersome but correct, not sure whether it will be possible for other commands/might require changes in Emacs.
• Should we export exwm--fake-key? I think it is very useful; might allow users to script other applications with Emacs. What kind of interface do we need?

[eval-on-point]

I don't know about scroll-other-window, because that is a feature that I do not use. A similar idea that I have had before is something like evil-collection for EXWM. The idea would be to provide a curated set of simulation keys for commonly used applications such as Chromium, XTerm, Firefox, Discord, Slack, etc. Maybe this could be designed in a way such that it is simple to implement things like scroll-other-window for each of these applications.

I don't have the time to commit to helping with this, but I think it is an interesting idea.

[medranocalvo]

Thank you for your thoughts @eval-on-point.

The fact that the keybinding is not standard across applications suggests that it might indeed belong in such a collaborative configuration project and not in EXWM itself.

I find the exwm-collection idea interesting as well. I wonder whether there is a small set of Emacs commands generally applicable to X applications which we can configure via exwm-manage-configurations. (Thinking about it, exwm-manage-configurations might be a good place to configure the per-application simulation key for scroll-other-window commands...).