Summary
When Android system default font is bolded/replaced (e.g. Xiaomi MiSans Pro Bold / 'full bold' setting), auto-width components are measured with Typeface.DEFAULT while rendering uses the TextView default typeface which inherits the system font configuration. The measured width is therefore too small, and the last glyph can be clipped or missing.
Example: English renders as Englis on Xiaomi with the system-wide bold font enabled.
Environment
- React Native 0.78.3 (Fabric / Bridgeless)
- Android 16 (API 36), Xiaomi HyperOS with system font set to
MiSans Pro Bold
- Reproduced on multiple Xiaomi devices
Root cause
TextLayoutManager.updateTextPaint() resets the paint typeface to null (Typeface.DEFAULT) when no explicit font family/weight/style is set, while ReactTextView renders with the TextView default typeface which carries the system bold/replacement config. Different metrics and advances mean measurement is narrower than what is actually drawn.
On device, same 48px text:
|
ascent |
descent |
line height |
measurement paint (Typeface.DEFAULT) |
-45 |
3 |
1.0em |
| rendering TextView (system bold) |
-50 |
14 |
1.33em |
English (7 glyphs): measured width 53.33dp (only 6 glyphs laid out), drawn width 56.67dp (7 glyphs). The final h is dropped.
Suggested fix
Make the measurement typeface the same source as rendering when no explicit font family/weight/style is set. A local patch that uses the system/default TextView typeface for measurement fixes the issue and was verified on 5 Android devices.
Additional context
This analysis and the local fix were produced with the assistance of an AI coding agent (Codex). Please review independently.
Related
Summary
When Android system default font is bolded/replaced (e.g. Xiaomi MiSans Pro Bold / 'full bold' setting), auto-width components are measured with Typeface.DEFAULT while rendering uses the TextView default typeface which inherits the system font configuration. The measured width is therefore too small, and the last glyph can be clipped or missing.
Example:
Englishrenders asEnglison Xiaomi with the system-wide bold font enabled.Environment
MiSans Pro BoldRoot cause
TextLayoutManager.updateTextPaint()resets the paint typeface to null (Typeface.DEFAULT) when no explicit font family/weight/style is set, whileReactTextViewrenders with the TextView default typeface which carries the system bold/replacement config. Different metrics and advances mean measurement is narrower than what is actually drawn.On device, same 48px text:
Typeface.DEFAULT)English(7 glyphs): measured width 53.33dp (only 6 glyphs laid out), drawn width 56.67dp (7 glyphs). The finalhis dropped.Suggested fix
Make the measurement typeface the same source as rendering when no explicit font family/weight/style is set. A local patch that uses the system/default TextView typeface for measurement fixes the issue and was verified on 5 Android devices.
Additional context
This analysis and the local fix were produced with the assistance of an AI coding agent (Codex). Please review independently.
Related