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Nudge

The arrow keys are the editor's precision instrument: a keyboard delta applied to whatever the current state says the arrows mean. This document specifies the whole family. The masks that keep the chords unambiguous are in the keybindings sheet; the state arbitration is routing; the quantization behavior nudge shares with gestures is snap.

Translate nudge — Arrow / Shift+Arrow​

With a node selection, arrows translate it by 1 unit along the axis; Shift multiplies by the big-nudge factor (default 10; a configuration value, not a second command).

  • The delta is applied exactly — nudge is never snapped to geometry (SNAP-4/SNAP-6 territory: quantization applies only when pixel-grid snapping is on, anchored so repeated sub-unit nudges accumulate without drift).
  • A burst frames as one entry: rapid successive nudges commit as one history step; one undo restores the pre-burst position. The mechanism is framing, not merging — the gesture frame stays open across the burst and closes on a dwell boundary; the stack never merges committed entries (history, HISB-3).
  • Locked nodes don't nudge; a mixed selection nudges its unlocked members.

Alignment feedback — the advisory guide​

A drag shows snap guides live as it moves; a keyboard nudge has no such in-gesture feedback — the object jumps a unit and stops. So when a translate nudge lands flush with an alignment — an edge or center level with a sibling or a guide — the editor flashes the snap guide that would have marked it, briefly, then clears it.

This is feedback, not snapping. The nudge delta is still applied exactly (NUDGE-1 / SNAP-6): the guide reveals an alignment the motion happened to hit; it never corrects the value toward one. It answers "did I just line these up?" for a gesture that, unlike a drag, gave no running answer.

  • Keyboard-only by nature. A drag owns its live guides — hidden on release, since an aligned drag needs no afterimage. The advisory guide exists precisely to give the guideless keyboard path the confirmation the pointer path already has; it is not a general post-translate affordance. (A programmatic translate delta, having no live guide either, may ride the same mechanism, but the UX is authored for the keyboard.)
  • Shows at once, holds briefly. It appears the frame the nudge lands and clears after a short hold (the reference editor: ~500 ms), re-arming on each successive nudge so a burst of arrows keeps it alive, then letting it fade once the keys stop.
  • It reveals, it does not correct. The affordance reuses snap's guide chrome and its detection (open a session, test the landed position) but drives no delta — snap's guide-rendering and value-correction halves are separable, and this uses only the first (snap.md, SNAP-8).

In-flow reorder​

A child under a layout container's flow (an auto-layout item with no authored insets) has no free position to translate — for it, the arrows reorder: the arrow pointing along the layout axis moves the node one slot forward/backward in the flow. A mixed selection splits: in-flow members reorder, out-of-flow members translate, in the same command. This is the property panel's computed-vs-authored rule (properties PROP-5) applied to the keyboard: never author a value the layout will immediately override.

Resize nudge — Mod+Arrow / Ctrl+Alt+Arrow​

Grows or shrinks the selection: right/left = width ±1, down/up = height ±1; Shift applies the big-nudge factor. Two chords bind it, either firing the same command — Mod+Arrow (the one-hand chord, Cmd on macOS) and Ctrl+Alt+Arrow — so a platform that reserves one (Cmd+Arrow for caret motion, Ctrl+Alt+Arrow for screen rotate) leaves the other free. Neither is move: move nudge requires Mod and Ctrl absent (keybindings, KEY-2). Semantics:

  • The anchor is the node's origin (top-left): position is fixed, the far edge moves — the keyboard twin of dragging the SE handle.
  • Per-element, not a union resize: a multi-selection grows each member about its own origin — every node keeps its position and takes the delta — rather than scaling the selection bounds as one box (the SE-handle drag resizes the union; this does not).
  • All-or-nothing gate: if any selected member is not resizable (auto-sized, or otherwise refusing), the command declines for the whole selection rather than resizing a subset.
  • Bursts frame exactly as translate nudges do.

Sub-mode nudges​

Inside content-edit modes the same arrows re-target (the routing capture order, not new bindings):

  • Vector edit: arrows translate the sub-selected vertices and tangents by the same 1/10 deltas (vector-edit).
  • Gradient edit: arrows move the selected stop's offset by 1% (Shift: 10%), clamped to [0, 1].

Empty selection — camera pan​

With nothing selected and no content-edit mode active, arrows pan the camera: the viewport moves a fixed screen-space step (default 50 px; Shift applies the big-nudge factor) in the arrow's direction. The step is screen-space — zoom does not change the felt distance. This is deliberate: arrows always do something spatial, and with no object to move, the camera is the object. Camera panning is view state — no document mutation, no history entry.

Contracts​

  • NUDGE-1 Exactness: a nudge of (+1, 0) changes the target's position by exactly (+1, 0) — no geometry snapping; with pixel quantization on, repeated 0.1-unit nudges accumulate on the anchored lattice without drift.
  • NUDGE-2 Burst framing: N rapid nudges frame into one history entry (the gesture stays open across the burst, closing on dwell); one undo restores the pre-burst state. Committed entries are never merged (HISB-3).
  • NUDGE-3 Resize nudge anchors the origin: position is unchanged, size changes by the delta; if any selected member refuses, nothing resizes.
  • NUDGE-4 In-flow reorder: an auto-layout child with no authored insets reorders along the layout axis instead of translating; its siblings' authored properties are untouched.
  • NUDGE-5 Empty-selection arrows pan the camera by the fixed screen-space step regardless of zoom, and record nothing.
  • NUDGE-6 Advisory guide: when a translate nudge lands the selection flush with a snap anchor (a sibling edge/center or a guide), a snap guide marks the alignment, holds briefly, then clears; the applied delta is unchanged (NUDGE-1 / SNAP-6 — feedback, never correction). A nudge that lands on no alignment paints nothing, and no other translate path (drag, panel entry) raises it.