Touchscreen support in vertico-mouse.el

[zigmhount]

Hello,
First, thanks for your work on vertico :)
I'm a beginner with Emacs, and I'm using it on Linux (v29 and 30) and Android (native build v30).

The native Emacs completion framework can be used with a touchscreen to scroll through and select candidates, but it does so in a separate buffer. I tried using vertico-mouse.el, and it works very well on Linux, but not at all with Android's touchscreen, neither scrolling nor tapping, whether in the minibuffer or in vertico-buffer. I have tested this with emacs -Q, M-x package-install vertico, M-x vertico-mode, M-x vertico-mouse-mode (ensuring that context-menu-mode is disabled).

I don't really know how to troubleshoot, but for scrolling, I am guessing (perhaps naively) that it might be due to the fact that vertico-mouse.el directly maps mwheel-scroll-up-function and mwheel-scroll-down-function to vertico--goto. Would it be as simple as adding a mapping between touchscreen-scroll window dx dy (Touchscreen Events in Emacs manual) and vertico-goto? what would the code look like?

For tapping, I don't really understand if touch-screen-track-tap should be mapped to vertico-mouse--click or if touch-screen-track-tap is already supposed to default to mouse-1 - in which case it should work out of the box and I may have another problem.

I'm also open to suggestions for other completion frameworks that may be supporting my use case, with a preference with displaying candidates in the minibuffer (icomplete-mode supports touchscreen actions in a buffer, but ivy-mode doesn't support them in the minibuffer).
Thanks!

[minad]

Touchscreen support is not implemented right now, see 66e2c47. Help adding this is welcome. I haven't looked into this yet, in particular on Android, since support for that is relatively new.

[misohena]

Hello,
Thank you for the great package!

I've also noticed this issue while using Emacs on Android.

So I tried writing the following code:

(defun my-vertico-touchscreen-begin (begin-event)
  (interactive "e")
  (let* ((begin-posn (cdadr begin-event))
         (begin-window (posn-window begin-posn))
         (begin-xy (posn-x-y begin-posn))
         (moved nil))
    (with-selected-window begin-window
      (let ((begin-scroll-pos vertico--scroll))
        (while
            (let ((ev (read-event)))
              (pcase (car-safe ev)
                ('touchscreen-update
                 (let* ((update-xy (touch-screen-relative-xy (cdaadr ev) begin-window))
                        (dx (- (car update-xy) (car begin-xy)))
                        (dy (- (cdr update-xy) (cdr begin-xy))))
                   (when (and (not moved)
                              (>= (+ (* dx dx) (* dy dy)) 2))
                     (setq moved t))
                   (when moved
                     (let* ((dline (/ dy (default-line-height)))
                            (new-scroll-pos (- begin-scroll-pos dline)))
                       (cond
                        ((< new-scroll-pos vertico--scroll)
                         (vertico--goto (+ new-scroll-pos vertico-scroll-margin)))
                        ((> new-scroll-pos vertico--scroll)
                         (vertico--goto (+ new-scroll-pos vertico-count
                                           (- vertico-scroll-margin))))))
                     (vertico--exhibit)))
                 t)
                ('touchscreen-end
                 (unless moved
                   (vertico--goto (vertico-mouse--index begin-event))
                   (vertico-exit))
                 nil))))))))

(defun my-vertico-touch-setup ()
  (interactive)
  (vertico-mouse-mode)
  (define-key vertico-mouse-map (kbd "<touchscreen-begin>")
              #'my-vertico-touchscreen-begin))

In my limited testing, both scrolling by swiping and selection by tapping seem to work correctly in my environment.

There might still be things that need improvement, but I thought it might be helpful to share this.

;; Apologies if the English sounds strange — it's machine translated.

[zigmhount]

My level of elisp-fu is unfortunately not good enough to come up with a solution by myself, but thanks a lot @misohena , your solution seems to work indeed. I have some glitches though, but it may very well be related to the rest of my config. This will let me use vertico on mobile already, thanks!