# Platform metrics audit — Apple HIG, GNOME HIG, Fluent, KDE HIG

Why our controls read small and foreign next to native ones. Assessed 2026-11
against the primary sources: the libadwaita stylesheet (`libadwaita` `main`,
`src/stylesheet/**.scss`), WinUI 3 theme resources (`microsoft-ui-xaml`
CommonStyles) and the Learn design pages, Kirigami `units.cpp` + Breeze
`breezemetrics.h`/`breezestyle.cpp`, and the Apple HIG pages. Apple publishes
no pixel metrics, so macOS numbers are **measured on this machine via AppKit
`fittingSize`** — note the OS-version variance called out below. Queue entry:
[CHECKLIST.md](CHECKLIST.md) — "Platform metric fidelity".

## Verdict

Three real problems, none of them "spacing values are off by a bit":

1. **Heights.** `control_height` is derived as `1.75 × root_font_size`.
   Native platforms do not size controls that way — Windows fixes buttons at
   32px, GNOME and Breeze add fixed padding to the font height. Result: our
   buttons are −23% vs native on Windows, −18% on GNOME. The main "looks
   small" driver.
2. **Radii.** Only `radius.control` adapts per platform; `sm`/`overlay` are
   frozen at 4/10. Native overlay radii span 5px (KDE) to 15px (GNOME) — we
   are 5px off in both directions.
3. **Borders.** We paint `border_1()` on nearly everything (shadcn-style).
   That matches Windows and KDE and contradicts macOS and GNOME/libadwaita,
   whose controls are borderless fills at normal contrast. The "feels weird"
   driver.

Structural gap underneath the spacing complaint: **the theme has no spacing
tokens** — components hardcode gpui utilities (`p_1`, `px_2`, `gap_1p5`,
`min_w_56`), so platform rhythm (GNOME's 6px grid, KDE's 4/6/8) cannot be
expressed.

## What the platforms specify

### Apple / macOS

The HIG publishes no pixel metrics for macOS — verified across the buttons,
text-fields, toolbars, toggles, menus, windows, layout, sidebars, sheets,
materials and designing-for-macos pages. What is published: the type ramp
(body 13pt, min 10pt) and the 44×44pt hit-region rule. Everything else below
was measured locally (AppKit, regular control size, this macOS build):

| Control | Measured | Confidence |
|---|---|---|
| Push button | **24pt** (small 20, mini 16) | measured |
| Rounded text field | **24pt** | measured |
| Pop-up button / segmented | **24pt** / **24pt** | measured |
| Switch | **54×24** | measured |
| Checkbox (empty control) | **16×16** | measured |
| Slider control height | **16pt** | measured |
| Window titlebar | **32pt** on this build; 28pt on older macOS | measured, version-dependent |
| Body text | 13pt | published |

Border language: toolbar items and image buttons are *explicitly borderless*
("toolbar items don't include a bezel"); hierarchy is expressed by fill, not
borders; fields keep a hairline bezel; menus/popovers separate by shadow and
material, not borders. Concentricity rule: "buttons, text fields, headers,
and footers have corner radii that are concentric with bar corners" (rule
only, no values).

### GNOME / libadwaita

Exact values from the stylesheet; GTK px are logical pixels at 96dpi.

| Metric | Value |
|---|---|
| Button total height | min-height 24 + padding 5px 10px ⇒ **≈34px** |
| Entry | **34px** (border-box, no vertical padding) |
| Header bar | **47px** |
| Menu item | min-height **32px**, padding `0 12px`; container padding 6px |
| Switch | knob 20px, trough ≈**46×26** |
| Checkbox | 14px + 3px pad each side ⇒ **20px**, radius **6px** |
| Radius ladder | button/entry **9px** (`$button_radius`), checkbox 6px, cards 12px, menu/popover/dialog/window **15px**, menu items 9px |
| Font | Adwaita Sans 11pt = **14.67px** |
| Focus | **2px accent outline** (accent @50% default, 80% high contrast) |

Borders: **controls are borderless at normal contrast** — raised buttons,
entries, switches, menus draw shape from translucent `currentColor`-mix
fills. 1px borders are a high-contrast affordance only. Always-on hairlines
are reserved for the window outline, headerbar bottom shade, frames, and
boxed-list row separators.

### Windows 11 / WinUI 3 (Fluent 2)

Published tokens from the theme-resource XAML and Learn pages, at 100%
scaling:

| Metric | Value |
|---|---|
| Button | **32px** (padding 11,5,11,6 + 1px border + Body 14/20); `ButtonHeight=32` lives in OS generic.xaml |
| TextBox | **32px** (`TextControlThemeMinHeight`, OS generic.xaml — not fetched) |
| CheckBox box | **20×20**, 1px stroke (row 32) |
| ToggleSwitch | track **40×20** pill; knob **12×12** resting → 14 hover |
| Radius | ControlCornerRadius **4px**, OverlayCornerRadius **8px** |
| Title bar | **32px** standard, 48px "Tall" |
| Type ramp | Caption 12, Body **14**, Body Large 18, Subtitle 20, Title 28 |
| Spacing | 8 between buttons, 12 control↔label, 16 edge↔text — a **4px grid** |
| Focus | system ring drawn outside the control (negative focus margin) |

Borders: buttons and textboxes carry a **1px elevation border** (gradient
stroke, lighter top + darker bottom); the accent button keeps a border too;
checkbox box 1px; switch track 1px while off; slider borderless except the
thumb.

### KDE Plasma 6 / Breeze

Source constants (`breezemetrics.h`, `units.cpp`); the HIG names the usage
rules, not px.

| Metric | Value |
|---|---|
| Kirigami units | gridUnit **18**, smallSpacing **4**, mediumSpacing **6**, largeSpacing **8**, cornerRadius **5** |
| Button | fontHeight + 2×(6+2) ⇒ **≈33px** at the default 10pt font |
| Line edit | fontHeight + 12 ⇒ **≈29px** |
| Checkbox | **20×20**, radius 4 |
| Switch (qqc2) | **36×18**, knob 18 |
| Radius | **5px** everywhere — buttons, line edits, menus, popups, windows |
| Font | Noto Sans 10pt = **13.33px** |
| Titlebar (KWin) | max(fontHeight, 2×gridUnit = 36) + margins ⇒ **≈44px** |
| Focus | rounded ring filled highlight @30%; item views get a focus underline |

Borders: 1px outline (`PenWidth::Frame`) on all controls; **flat buttons are
borderless until hover/press/check**; menus and popups framed 1px.

## What our tokens resolve to today

`SizeTable::with_root_font_size` medium class (height 1.75rem, padding
1rem) fed by each adapter's inputs in `crates/theme/src/source/`:

| | macOS (root 13) | Windows (root 14) | GNOME (fallback 16) | KDE (fallback 16) |
|---|---|---|---|---|
| control_height | 22.75 | 24.5 | 28 | 28 |
| input_height | 24 (stated) | 32 (stated) | 30 | 30 |
| padding_x | 13 | 14 | 16 | 16 |
| text / icon / indicator | 13 / 13 / 15.9 | 14 / 14 / 17.2 | 16 / 16 / 19.6 | 16 / 16 / 19.6 |
| radius sm / control / overlay | 4 / 6 (stated) / 10 | 4 / 4 (stated) / 10 | 4 / 6 / 10 | 4 / 6 / 10 |
| titlebar | max(22.75, 34 floor) = 34 | 32 (stated) | 34 | 34 |
| switch (1.65×h × h, knob 1.225rem) | 37.5×22.75 | 40.4×24.5 | 46.2×28 | 46.2×28 |

## Gap analysis

### Heights — the "looks small" bug

| Button height | Native | Ours | Delta |
|---|---|---|---|
| Windows | 32 | 24.5 | **−7.5px (−23%)** |
| GNOME | ≈34 | 28 | **−6px (−18%)** |
| KDE | ≈33 | 28 | −5px |
| macOS | 24 | 22.75 | −1.25pt |

Root cause: native heights are not `k × font`. Windows fixes 32px; GNOME is
font + 10px padding; Breeze is fontHeight + 16px. One rem factor cannot hit
any of them — and the trap is that reading the real Linux fonts (14.67 /
13.33px) without changing the model makes our buttons *smaller* (24.4 /
23.3). The codebase already has the right seam: `SystemTheme.input_height`,
an optional platform-stated value with ratio scaling for the other classes.
`control_height` needs the same treatment. Our stated `input_height` values
(macOS 24, Windows 32) are already exactly right — the derived button height
next to them is what is off.

Text compounds it on Linux: the GNOME/KDE adapters never state
`root_font_size`, so the 16px fallback makes labels oversized (16 vs 14.67 /
13.33) while controls read undersized.

### Radii

| Radius | macOS | Windows | GNOME | KDE |
|---|---|---|---|---|
| control | 6 ~ bezel ≈6 | 4 ✓ | **6 vs 9** | 6 vs 5 ~ |
| overlay (menu/popover/dialog) | 10 ~ (unpublished, ≈10–12) | **10 vs 8** | **10 vs 15** | **10 vs 5** |
| sm (checkbox) | 4 ~ | 4 ~ | 4 vs 6 | 4 ✓ |

Only `control` is platform-overridable (`resolve`); `Radius::default`
freezes sm/overlay/full. GNOME's whole ladder sits 3–5px above ours; KDE's
overlays sit 5px below.

### Borders — the "feels weird" bug

Our current policy: `border_1()` on secondary button, input, select,
checkbox, radio, menu, popover, dialog, combobox popup, command palette,
toast, tooltip, alert, even slider/switch knobs. Primary button is
borderless.

| Element | macOS | GNOME | Windows | KDE | Ours |
|---|---|---|---|---|---|
| secondary button | fill, **no border** | fill, **no border** | 1px elevation border | 1px border | 1px — ✗mac/GNOME |
| primary button | fill, no border | fill, no border | **accent fill + border** | accent fill + border | no border — ✗Win/KDE |
| input | hairline bezel | **borderless**, 2px accent outline on focus | 1px border → accent on focus | 1px border → focus color | 1px always |
| menu / popover | **no border** (shadow/material) | no border (shadow + 1px black@5% ring) | framed flyout | 1px frame | 1px |
| separator roles | hairline ✓ | hairline ✓ | ✓ | ✓ | ✓ |

Half-right on Windows/KDE, systematically wrong on macOS/GNOME — and even on
Windows/KDE our primary button drops a border the natives keep. Our
high-contrast mode sharpening borders toward the foreground is exactly
GNOME's model (borders as a high-contrast affordance); it just never
switches off at normal contrast.

### Spacing — structural, not numeric

No spacing tokens exist in `Theme`; components hardcode a fixed 4px grid:
menu `p_1` + items `px_2 py_1`, popover `mt_1 min_w_32`, menu `min_w_56`,
toast/tooltip `px_3`/`px_2 py_1`, button `gap_1p5`, hardcoded
`max_w(480)`/`max_w(360)`. Native rhythms: GNOME = 6px base (menu padding
12px, item min-height 32px — our GNOME menu rows ≈24px), KDE = 4/6/8,
Windows and macOS ≈ 4px grid (we happen to match those two). Menu/popover
density is frozen at a macOS-ish tuning.

### Per-component calibration

- **Switch**: macOS native 54×24 (ours 37.5 wide — too narrow); Windows
  40×20 with a 12px knob (ours 24.5 tall, 17px knob — too big); KDE 36×18
  (ours 46×28); only GNOME ≈ matches, by accident.
- **Checkbox**: Windows/GNOME/KDE ≈20 (ours 17.2–19.6); macOS 16 ✓.
- **Icons**: macOS ≈16 (ours 13), Windows 16 (ours 14); GNOME/KDE 16 ✓.
- **Titlebar**: measured 32 on this macOS build vs our 34 floor (fine-ish;
  the floor silently drifted past older macOS's 28); GNOME headerbar 47 vs
  34 — a visible −13px; KDE ≈44 vs 34; Windows 32 stated ✓.

## What is already right

- The `input_height` stated-value seam — the pattern to generalize.
- Windows `ControlCornerRadius` 4; stated titlebar 32.
- Body text on macOS (13) and Windows (14); scrollbar autohide mapping;
  per-platform elevation stacks; high-contrast border sharpening mirrors
  GNOME's model.
- GNOME accent via portal/gsettings, KDE `DecorationFocus`/`DecorationHover`
  role mapping.

## Recommended changes, in priority order

1. **State `control_height` per platform** — add `control_height:
   Option<Pixels>` beside `input_height` on `SystemTheme`, reuse the
   ratio-scaling pattern: macOS 24 (measured), Windows 32, GNOME ≈34, KDE
   ≈33. Fixes the smallness everywhere in one change.
2. **State `root_font_size` from Linux font settings** — GNOME
   `font-name` (11pt ⇒ 14.67px), KDE `kdeglobals [General] font=` (10pt ⇒
   13.33px); the parsing seams already exist for colors.
3. **Make the radius ladder platform-overridable** — stated overlay/sm
   radius on `SystemTheme`: GNOME 15/6, Windows 8/4, KDE 5/4, macOS ≈10/4;
   keep preset > system precedence.
4. **Per-source border and focus policy** — a theme-level token consumed by
   components: secondary button and inputs drop borders on macOS/GNOME
   (fill tints + 2px accent focus outline), keep 1px on Windows/KDE;
   primary gains a border on Windows/KDE; menus/popovers shadow-only on
   macOS/GNOME.
5. **State `titlebar_height` per platform** — GNOME 47, KDE ≈44; macOS
   queried rather than a drifted floor (32 on current builds, 28 older);
   Windows stays stated.
6. **Add a minimal spacing scale to `Theme`** driven by a per-platform base
   unit (GNOME 6, KDE 4/6/8, others 4); route menu/popover paddings, menu
   item min-height (GNOME 32), and the hardcoded `min_w_`/`max_w` values
   through it.
7. **Calibrate switches and icons per platform** — macOS 54×24, Windows
   40×20 with 12px knob, KDE 36×18; icon 16 on macOS/Windows.

## Source confidence notes

Everything in the GNOME/Windows/KDE tables is quoted from the cited
stylesheets, sources, or Learn pages (published). KDE button/line-edit/title
heights are formulas from source constants (derived). Windows TextBox height
token and the focus-stroke pixel spec live in the OS `generic.xaml` and were
not retrievable — low confidence, commonly cited as 32. Apple publishes no
macOS control metrics; all macOS control numbers here are AppKit
measurements from 2026-11 on this machine and may shift across macOS
releases (titlebar already differs from older builds).