Crate makeover_geometry 

The invariant half of the make-family design system.

[makeover] resolves colour, which varies by theme. This crate carries everything that does not: spacing, radius, border width and the type scale. The split is the same one Balanced Breakfast’s theme contract has always drawn — a theme overrides colour tokens only — moved out of two app stylesheets so the three consumers stop maintaining three copies of it.

Spacing is relational, not numeric

The Mac OS 8 Human Interface Guidelines specify white space by what two things are being separated, never by a size name, and define no base grid unit. A control and its satellite pop-up are set 4 pixels apart; peers stacked in a list get 6; a group box’s inner margin is 10; separated groups and rows of push buttons get 12.

That vocabulary is the primary interface here. Gap names the relationship and the size follows from it, exactly as surface-raised names an intent and the hex follows from it. The raw Step scale exists underneath for distances a relationship does not describe, but reaching for it is a smell worth a second look.

Naming the relationship is what makes the rule reviewable. Whether a gap should be 6px or 8px is unanswerable in isolation; whether two things are peers is not.

Ratios, not pixel counts

This is the deliberate departure from the HIG, which is specified in hard device pixels because in 1997 there was one pixel density and one text size. Every Step here is a Ratio of a single base unit, so the whole system scales from one knob: --geometry-base, 1rem by default.

At the default base the ratios land exactly on the HIG’s numbers — Snug is three eighths of 16px, which is 6px — so nothing is lost in the translation. What is gained is that the layout tracks the user’s text size instead of fighting it, an accessibility setting becomes one value rather than a sweep, and the scale means the same thing at any display density.

Density presets

Naming relationships instead of sizes is what makes a density preset possible at all. Density changes what each relationship resolves to without touching a single call site, because no call site names a size. The mobile and desktop builds of a Tauri app should differ mostly by which preset they emit, not by a parallel set of hand-written mode-scoped rules.

The two presets are not one scaled copy of the other, and the asymmetry is the point — it is also why a base scalar alone cannot express this. Touch needs more room between things you tap, because a fingertip is coarser than a pointer, and less room around the edges, because the screen is small and outer margin is screen you do not get to use. So Peer and Section open up under Density::Touch while Pane and Page tighten. Bound never moves: it is the one relationship that says “these are one object”, and separating them on touch would say the opposite.

Surfaces, and why a TUI is not a third density

Surface is the third axis and the one that carries this to alloy_tui. A terminal is not a density preset; it is a surface whose smallest representable step is one cell rather than one pixel. Give Ratio::quanta a quantum and it answers in whole units of it, so the relational vocabulary crosses to a character grid with nothing added.

Quantising is not a terminal special case either — a display quantises to the pixel. It is only that rounding 6.0 to the nearest pixel is uninteresting, while rounding three eighths of a cell to the nearest cell decides the layout.

On Surface::terminal the pointer preset resolves to 0, 0, 1, 1, 2, 2 cells. Bound and Peer collapsing to nothing is correct rather than lossy: in a grid that dense, both relationships are expressed by adjacency. A coarse surface genuinely has fewer distinctions available, and the model should say so instead of inventing a gap to keep six names distinct.

So the three axes are: Gap is what is being separated, Density is who is operating it, Surface is what it is drawn on.

Structs

Ratio

A fraction of the base unit.

Surface

What the layout is being drawn on: a base unit, and the smallest step the surface can actually represent.

Enums

Density

Which input the layout is being sized for.

Gap

A named separation between two things.

Step

A raw step on the underlying scale.

Constants

BASE_TOKEN

The CSS custom property every ratio scales from.

DEFAULT_BASE_PX

The default base unit in CSS pixels, at a 16px root font size.

Functions

density_css

The whole spacing layer with the canonical density selection, as CSS.

gap_css_declarations

Emit the relational layer for one density as CSS declarations, no selector.

gap_css_overrides

Emit a density preset as a scoped override block.

geometry_css_vars

Emit the whole geometry layer as a :root { … } block at one density.

scale_css_declarations

Emit the base unit and the raw scale as CSS declarations, no selector.