🐛(frontend) center Avatar initials with a font-aware cap-height ratio

The previous implementation centered initials by measuring `<text>`
with `getBBox()`, which returns the font's advance-width by
ascent-to-descent band, not the ink of the glyphs. On fonts with an
asymmetric band, initials rendered off-center. Marianne is a
particularly clear case: ascent 1131 / descent 256 puts the band
center 87.5/1000 above the caps' optical center, so every avatar
sat ~4.6 viewBox units (~1.5–1.8 px) too low. A follow-up rewrite
using canvas `actualBoundingBox*` metrics fixed it but pulled in a
runtime measurement rig (shared canvas, ref, state, layout effect,
`fonts.load` + `loadingdone`, plus combining-mark stripping) just
to place two uppercase letters.

Since initials are always uppercased, optical centering has a
closed form: `baseline = center + capHeight/2`. Real-world text
fonts have cap heights in a narrow ~0.66–0.73 em band (Marianne is
0.70), so:

    translateY(calc(var(--avatar-cap-height, 0.7) * 0.5em))

is exact for the stock font and within ~0.4 px for any plausible
replacement. No JS, SSR-safe, no first-paint jump, no font-loading
race. Accents float above the cap box instead of dragging the
letter down.

The single font-dependent number remaining (cap height) is exposed
as a CSS variable, so self-hosters overriding the font can override
it next to the font itself, or leave the default. Once
`text-box: trim-both cap alphabetic` ships broadly, even the
variable can go.

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to
 - 🐛(backend) allow any printable ASCII characters in user sub field #1673
 - 🐛(frontend) keep the sending resolution picked while the camera is off #1667
 - 🐛(frontend) restore automatic lower-hand on speaking
+- 🐛(frontend) center Avatar initials with a font-aware cap-height ratio
 
 ## [1.30.0] - 2026-09-01
 

docker/dinum-frontend/dinum-styles.css

@@ -1,5 +1,6 @@
 :root {
     --fonts-sans: 'Marianne', ui-sans-serif, system-ui, sans-serif;
+    --avatar-cap-height: 0.7;
 }
 
 .Header-beforeLogo {

docs/theming.md

@@ -34,6 +34,7 @@ Let's say you want to change the font of our application to a custom font. You c
 
 :root {
   --fonts-sans: 'Roboto', ui-sans-serif, system-ui, sans-serif;
+  --avatar-cap-height: 0.7;
 }
 ```
 

src/frontend/src/components/Avatar.tsx

@@ -1,5 +1,5 @@
 import { css, cva, RecipeVariantProps } from '@/styled-system/css'
-import React, { useLayoutEffect, useMemo } from 'react'
+import React, { useMemo } from 'react'
 
 const avatar = cva({
   base: {
@@ -28,24 +28,17 @@ const avatar = cva({
   },
 })
 
-// Instantiating a segmenter is expensive; create it once and reuse it.
 const graphemeSegmenter =
   typeof Intl !== 'undefined' && 'Segmenter' in Intl
     ? new Intl.Segmenter(undefined, { granularity: 'grapheme' })
     : undefined
 
-/**
- * Returns the first user-perceived character. Some Unicode characters span
- * multiple UTF-16 code units, so a naive index into the string can split them
- * and yield a broken glyph.
- */
 const getFirstGrapheme = (value: string): string => {
   if (!value) return ''
   if (graphemeSegmenter) {
     const [first] = graphemeSegmenter.segment(value)
     return first?.segment ?? ''
   }
-  // Fallback: keeps single code points intact (including surrogate pairs).
   return Array.from(value)[0] ?? ''
 }
 
@@ -66,36 +59,6 @@ export type AvatarProps = React.HTMLAttributes<HTMLDivElement> & {
 export const Avatar = React.memo(
   ({ name, bgColor, context, notification, style, ...props }: AvatarProps) => {
     const initials = useMemo(() => getInitials(name), [name])
-    const textRef = React.useRef<SVGTextElement>(null)
-    const [offsetY, setOffsetY] = React.useState(0)
-
-    // Optically center the initials: measure the ink bounding box of the
-    // rendered glyphs and shift them so the box's center sits at the middle
-    // of the viewBox. Works for any font, weight or glyph shape, unlike a
-    // hand-tuned dy offset. getBBox() is in local (pre-transform)
-    // coordinates, so applying the translation never changes the measure.
-    useLayoutEffect(() => {
-      const text = textRef.current
-      if (!text) return
-
-      const center = () => {
-        const box = text.getBBox()
-        // A hidden element measures as an empty box; keep the default then.
-        if (box.height === 0) return
-        setOffsetY(50 - (box.y + box.height / 2))
-      }
-
-      center()
-      // Glyph metrics can change once webfonts finish loading.
-      let cancelled = false
-      document.fonts?.ready.then(() => {
-        if (!cancelled) center()
-      })
-      return () => {
-        cancelled = true
-      }
-    }, [initials])
-
     return (
       <div
         style={{ backgroundColor: bgColor, ...style }}
@@ -108,15 +71,16 @@ export const Avatar = React.memo(
           className={css({ width: '100%', height: '100%', display: 'block' })}
         >
           <text
-            ref={textRef}
             x="50"
-            y="50"
-            transform={`translate(0 ${offsetY})`}
+            y={50}
             textAnchor="middle"
-            dominantBaseline="central"
             fontSize="52"
             fontWeight="500"
             fill="currentColor"
+            className={css({
+              transform:
+                'translateY(calc(var(--avatar-cap-height, 0.7) * 0.5em))',
+            })}
           >
             {initials}
           </text>

src/frontend/src/styles/index.css

@@ -6,6 +6,10 @@ body,
   height: 100%;
 }
 
+:root {
+  --avatar-cap-height: 0.7;
+}
+
 html.font-lexend {
   --fonts-sans: 'Lexend Variable', ui-sans-serif, system-ui, sans-serif;
 }