[vertico-buffer] Buffer height insufficient when using mixed Chinese/English fonts due to different font heights

[tshu-w]

Problem

When using vertico-buffer-mode with mixed Chinese and English fonts that have different heights, the buffer height calculation becomes insufficient, resulting in incomplete content display.

Configuration

(setq vertico-buffer-display-action `(display-buffer-in-side-window
                                      (window-height . ,(+ 3 vertico-count))
                                      (side . top)))

Expected Behavior

The vertico buffer should display all candidates completely, regardless of font height differences between Chinese and English characters like mini-buffer.

Actual Behavior

• Chinese characters typically have greater height than English characters
• The calculated window-height (based on vertico-count + 3) doesn't account for this difference
• Content gets cut off or candidates are partially visible
• Scrolling may be required even when it shouldn't be necessary

Environment

• Emacs version: GNU Emacs 30.1 (build 1, aarch64-apple-darwin24.3.0, NS appkit-2575.40 Version 15.3.1 (Build 24D70)) of 2025-02-28
• Vertico version: 20250203.1055
• Font configuration:

(defvar default-font "MonoLisa")
(defvar font-size 14)
(defvar unicode-font "Noto Sans CJK SC")
(defvar unicode-scale (/ 18.0 font-size))
(defvar emoji-font "Noto Color Emoji")
(defvar symbol-font "Noto Sans Symbols")

(setq unicode-font "PingFang SC"
      emoji-font "Apple Color Emoji"
      symbol-font "Apple Symbols"))

(defun setup-font (&rest args)
    (set-face-attribute 'default nil :font (font-spec :family default-font :size font-size))

    (when (fboundp 'set-fontset-font)
      (dolist (charset '(kana han cjk-misc bopomofo))
        (set-fontset-font t charset unicode-font))
      (add-to-list 'face-font-rescale-alist `(,unicode-font . ,unicode-scale))
      (set-fontset-font t 'emoji emoji-font nil 'prepend)
      (set-fontset-font t 'symbol symbol-font nil 'prepend)))

[minad]

Vertico and Corfu both assume monospaced characters as of now. This is difficult to improve.

[tshu-w]

I see, I have used vertico-multiform-mode for this case.

[minad]

Feel free to post your solution somewhere, or add it to the Vertico wiki. It would be nice to lift these mono space restrictions, but unfortunately Emacs pixel computations are somewhat weak. For example string-pixel-width is inefficient. If we would resize the window or adjust the number of candidates based on pixel computation I am afraid that it would add quite a bit of latency, since we would have to recompute once per update.

[tshu-w]

Yes, I studied it for a while and didn't find any good solutions. I modified the vertico-buffer-display-action setting of consult-location through vertico-multiform-categories to display it from the right instead of from the top.