Add lineHeight to ITerminalOptions

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Évaluation

Difficulté
4/5
Temps estimé
3-5 jours
Accessibilité débutants
48/100
Type d'issue
Fonctionnalité
Clarté
Clairement spécifiée
Activité
Active
Stack technique
typescript
Domaine
api, frontend

Piste de recherche

Start with ITerminalOptions, CanvasRenderer.measureFont(), charHeight, and remeasureFont() named in the issue. Read xterm.js 6.0’s lineHeight behavior and coordinate with the open issues #207, #146, and #126 because they touch related font metrics. Done means lineHeight is a runtime option with the stated default and multiplier behavior, glyphs remain centered, and the related metric changes are accounted for.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

Description

What's missing

There's no way to adjust line spacing. lineHeight appears nowhere in the published bundle, and the cell height is fixed by CanvasRenderer.measureFont():

const m = ctx.measureText("M"),
  ascent  = m.actualBoundingBoxAscent  || this.fontSize * 0.8,
  descent = m.actualBoundingBoxDescent || this.fontSize * 0.2,
  height  = Math.ceil(ascent + descent) + 2,   // the only leading, hardcoded
  baseline = Math.ceil(ascent) + 1;

charHeight returns metrics.height, and ITerminalOptions exposes fontSize and fontFamily but nothing for spacing — so there's no public knob and nothing private to reach for either.

Why

@xterm/xterm 6.0 has lineHeight?: number (xterm.d.ts:150), and xterm.js API compatibility is an explicit goal here — so this reads as a gap in that compatibility rather than a new feature. It's also the setting people reach for immediately after fontSize: we added runtime font-size controls, went to add line spacing beside them, and found it unavailable at any level.

Suggested shape

Matching xterm.js so existing code ports unchanged:

interface ITerminalOptions {
  lineHeight?: number;   // multiplier of measured line height, default 1.0
}

Feeding the same expression — roughly height = Math.ceil((ascent + descent) * lineHeight) + 2 — with the baseline offset by half the added leading so glyphs stay centred in the taller cell (xterm.js does this), and picked up by remeasureFont() so it works as a runtime option change like fontSize already does.

Relationship to open issues

This touches the same function as several open issues and should be built on whatever they settle rather than in parallel:

  • #207 — Math.ceil → Math.round on the cell width
  • #146 — rounding metrics to device-pixel boundaries, including the height expression
  • #126 — the visible gap between ── box-drawing cells; the hardcoded + 2 vertical leading looks like part of that story, and anything that changes it interacts with a lineHeight multiplier
Environment
  • ghostty-web 0.4.0-next.21.g640db46 (npm next, published 2026-10-28,
    commit 640db46), and 0.4.0 (npm latest) — ITerminalOptions and
    CanvasRenderer.measureFont() are identical in both, and lineHeight
    appears in neither the typings nor the bundle.
  • Canvas renderer, FitAddon, Vite + TypeScript
Langage dominant
TypeScript
Étoiles
3.1k
Forks
202
Merge moyen
1 j 40 min
PR mergées (30 j)
1

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