fix(web): fit Nerd Font prompt glyphs to terminal cells by MangoSwirl · Pull Request #23026 · pingdotgg/t3code

MangoSwirl · 2026-10-21T18:21:39Z

Problem

Nerd Font prompts such as oh-my-posh look mangled in the integrated terminal because their glyphs don't fit the terminal's cells:

The rounded Powerline caps U+E0B4 and U+E0B6 come from the font. The glyph doesn't fill the cell, so each cap is notched against its segment's background.
Columns start at fractional x positions. Every Powerline separator, including the solid triangles from fix(web): render powerline separators at cell edges #5607, leaves a thin antialiased seam against its neighbor.
Nerd Font icons are usually wider than a cell. An icon is drawn as part of a text run that is clipped to its cells and squeezed to the run's width. The Ubuntu logo loses its right half under the cap that follows it. The GitHub upstream icon spills over the branch icon right after it and hides it completely.

Native Ghostty avoids all of this by drawing Powerline shapes as cell geometry and constraining icons to their cells. This PR does the same in our Canvas renderer.

Fix

This is a small fix for an obvious rendering bug, so it doesn't need a prior issue or discussion. It follows the approach of #5607. It touches only apps/web/src/terminal/ghostty/renderer.ts.

Round caps: U+E0B4 and U+E0B6 join the solid separator path. They are drawn as the half circle Ghostty uses (src/font/sprite/draw/powerline.zig): radius min(cell width, cell height / 2), cubic Béziers with the usual quarter-circle kappa, and a straight edge between the arcs when the cell is tall.
Seams: the separator shape is grown out to whole device pixels: the left edge is floored and the right edge ceiled, using the canvas transform's scale. It slightly overlaps its neighbors instead of leaving an antialiased seam. This applies to the existing triangles too.
Icons: Private Use Area glyphs are drawn one at a time instead of inside text runs. Following Ghostty's rule, an icon may spread into the next cell when that cell is blank and the previous cell isn't also an icon. It is then shrunk to fit the room it has and centered. An icon that already fits, such as the clock, is drawn exactly as before.

Web and desktop share this renderer. Mobile uses libghostty's own sprite glyphs and is unaffected.

#21641 also touches fillSolidPowerlineSeparator, where it passes the snapped row height. It fixes a separate cursor-blink artifact. Whichever lands second needs a small rebase.

Before / after

Full-size prompt rows

Before (main):

After:

Captured from the terminal canvas in a real T3 Code dev build:

Environment: Linux, Chromium at device pixel ratio 2, JetBrainsMonoNL Nerd Font at 13px, dark theme, oh-my-posh prompt.
Method: the same terminal session was captured on this branch, then again with main's renderer.ts swapped in.
Result:
- On main, the leading cap has a seam and a notched outline, the separator edges show hairline seams, the Ubuntu logo is cut in half, and the GitHub icon covers the branch icon.
- On this branch the pill is continuous, and both icons are whole inside their own cells.

Verification

vp lint apps/web/src/terminal/ghostty/renderer.ts: passed
vp run typecheck in apps/web: passed
vp test run src/terminal/ghostty/core.test.ts src/terminal/ghostty/surface.test.ts: 44 passed
Manual check in the integrated terminal, as above

Not checked: fractional device pixel ratios such as browser zoom, the packaged Electron app, and macOS. My original report was from macOS Ghostty versus T3 Code; the capture above is from Linux.

Written with Claude Opus 5.5 via Claude Code in T3 Code.

- Draw rounded separators from cell edges to avoid fallback font gaps - Expand separator bounds to prevent antialiased seams

macroscopeapp · 2026-10-21T18:23:21Z

Approvability

Verdict: Approved at 6196e43

Macroscope's review found this PR approvable — This is a one-file, localized terminal-rendering fix that adds rounded Powerline separator geometry and removes visible seams in existing separators. Its runtime impact is limited to canvas presentation, with no schema, infrastructure, security, billing, or configuration-default changes.

^{You can add or adjust custom eligibility rules. Learn more.}

Icons wider than a cell were clipped by their text run or spilled under the next glyph. Draw each icon on its own and, like Ghostty, give it a following blank cell when one exists, then shrink and center it to fit.

coderabbitai · 2026-10-21T18:28:29Z

No actionable comments were generated in the recent review.

Walkthrough

The Ghostty renderer now draws rounded Powerline separators with device-pixel-snapped edges. It detects Nerd Font icons, fits them within one or two cells when conditions allow, and renders them separately from ordinary text.

Changes: Ghostty renderer glyph support

Layer / File(s)	Summary
Powerline separator geometry `apps/web/src/terminal/ghostty/renderer.ts`	The renderer recognizes rounded Powerline glyphs and draws rounded or triangular separators with device-pixel-snapped cell edges.
Nerd Font icon rendering `apps/web/src/terminal/ghostty/renderer.ts`	The renderer detects Nerd Font private-use glyphs, fits icons within available cell space, may use an adjacent blank cell, and renders icons separately from ordinary text runs.

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Bug fix

Suggested reviewers: sadrig91

Merge Risk: Minimal · up to 0992d

No actionable rendering risk remains from the reviewed changes. The adjacent-icon size limit preserves native Ghostty alignment.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: fitting Nerd Font prompt glyphs to terminal cells.
Description check		The description includes the problem, proposed fix, scope rationale, verification commands, manual results, screenshots, limitations, and agent attribution. The “Fix” heading serves the required chang…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description includes the problem, proposed fix, scope rationale, verification commands, manual results, screenshots, limitations, and agent attribution. The “Fix” heading serves the required change section, and the scope exemption is explained for this focused bug fix.

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Inline comments:
Review comments at @apps/web/src/terminal/ghostty/renderer.ts:
- Around line 65-66: Update the separator bounds calculation around cellLeft and
metrics.width to snap in device space using the canvas transform scale, then
convert the outward-rounded bounds back to logical coordinates. Preserve floor
expansion for left and ceil expansion for right so neither edge moves inward at
fractional device-pixel ratios.

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Inline comments:
Review comments at @apps/web/src/terminal/ghostty/renderer.ts:
- Around line 115-119: Update the span calculation near previousIsIcon so it
depends only on whether the following cell is blank, removing the previousIsIcon
restriction from the base span. Preserve the existing two-cell span for an icon
followed by a blank cell, allowing adjacent icons to use that blank cell while
leaving other cells at span 1.
- Line 132: Update the translation in the icon rendering path to use the cell’s
vertical midpoint, `top + metrics.height / 2`, instead of the baseline-based
`top + metrics.baseline - inkCenterOffset`; keep the horizontal centering and
existing `fillText` offset unchanged.

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…ound-powerline-caps

juliusmarminge · 2026-11-11T04:52:05Z

Evidence

Run each unchanged commit as the real web app, with a fresh synthetic project and replay thread.
Set JetBrainsMonoNL Nerd Font to 13px. Render actual oh-my-posh prompts with rounded caps, an Ubuntu icon immediately before a cap, and adjacent GitHub/branch icons. Render Starship through zsh with Catppuccin Mocha, beginning with [](red) and ending with [ ](fg:lavender).
Print both triangular separator directions at six successive cell offsets. Repeat at DPR 1.25, 1.5, and 2; require identical screenshots 500ms apart.

Environment on both sides: Chromium 156.0.8078.4, Linux web dev app, dark theme, 1440×1000 CSS viewport; oh-my-posh 32.0.0, Starship 1.27.0, zsh 5.9. Chromium uses --font-render-hinting=none, giving the 13px font a measured 7.800003px cell advance. Default Linux hinting rounded this to 8px and hid fractional edges at DPR 1.25/1.5. Both commits use the same setting.

All images below were independently rebuilt using the downloaded public source bundle, then inspected. Prompt crops use 2× nearest-neighbor enlargement; seam crops use 16× and show both U+E0B0 and U+E0B2 at the second cell offset.

Before	After
b3fdf2b10f	0992d1354b
DPR 2: caps and icons	DPR 2: caps and icons
DPR 1.25: triangular seams	DPR 1.25: triangular seams
DPR 1.5: triangular seams	DPR 1.5: triangular seams

Base shows cap notches, a clipped Ubuntu icon, overlapping adjacent icons, and dark vertical bands at triangle bases. Head has continuous cap joins, whole separate icons, and no vertical seam bands at either fractional scale.

Full app captures: DPR 1.25: before, after; DPR 1.5: before, after; DPR 2: before, after.

Reproduce: complete source bundle, font and configurations, seed.mjs, prompt.py, browser-driver.mjs, crop generator.

Rebuild records: verification, before manifest, after manifest, crop coordinates and pixel samples.

AI-assisted; verified with the tests and tools listed above.

github-actions · 2026-11-12T03:48:42Z

This PR conflicts with main. Rebase it or merge main into it. If it still conflicts after 7 days with no activity, it will be closed automatically.

See the conflict window.

fix(web): render rounded Powerline terminal separators

6196e43

- Draw rounded separators from cell edges to avoid fallback font gaps - Expand separator bounds to prevent antialiased seams

github-actions Bot added vouch:unvouched Author is not yet trusted in the VOUCHED list. size:M 30-99 changed lines (additions + deletions). labels Oct 21, 2026

MangoSwirl marked this pull request as draft October 21, 2026 18:23

macroscopeapp Bot approved these changes Oct 21, 2026

View reviewed changes

fix(web): fit Nerd Font icons inside their terminal cells

cc48694

Icons wider than a cell were clipped by their text run or spilled under the next glyph. Draw each icon on its own and, like Ghostty, give it a following blank cell when one exists, then shrink and center it to fit.

github-actions Bot added size:L 100-499 changed lines (additions + deletions). and removed size:M 30-99 changed lines (additions + deletions). labels Oct 21, 2026

MangoSwirl changed the title ~~fix(web): render rounded Powerline terminal separators~~ fix(web): fit Nerd Font prompt glyphs to terminal cells Oct 21, 2026

coderabbitai Bot reviewed Oct 21, 2026

View reviewed changes

Comment thread apps/web/src/terminal/ghostty/renderer.ts Resolved

fix(web): snap Powerline separator edges in device pixels

a21baec

MangoSwirl marked this pull request as ready for review October 21, 2026 18:40

coderabbitai Bot reviewed Oct 21, 2026

View reviewed changes

Comment thread apps/web/src/terminal/ghostty/renderer.ts Resolved

Comment thread apps/web/src/terminal/ghostty/renderer.ts Resolved

MangoSwirl and others added 2 commits October 21, 2026 11:50

fix(web): center constrained terminal icons in their cells

caea9e8

Merge remote-tracking branch 'origin/main' into mangoswirl/terminal-r…

0992d13

…ound-powerline-caps

joaomdsferro mentioned this pull request Nov 11, 2026

fix(web): draw rounded powerline caps to fill the terminal cell #34552

Merged

github-actions Bot added the needs-rebase Conflicts with its base branch. Closes after 7 days with no activity. label Nov 12, 2026

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fix(web): fit Nerd Font prompt glyphs to terminal cells - #23026

fix(web): fit Nerd Font prompt glyphs to terminal cells#23026
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