Drawing modifiers — ortho, polar tracking, dynamic input

These apply across all draw tools (rect, polygon, path, circle, arc) and the Move/Stretch translation modes.

Modifier	Default	Toggle	What it does
Ortho mode	off	`F8` or status-bar `ORTHO`	Constrains the next vertex / drag offset to horizontal or vertical. Hold `Shift` to invert (Shift always means "the opposite of current ortho").
Polar tracking	off	`F10` or status-bar `POLAR n°`	Locks the cursor onto the nearest n-degree ray from the previous vertex when within tolerance. The default step is 45°; change it in Edit → Settings (1–180°).
Dynamic input HUD	always on during drafts	n/a	A small floating panel shows the live distance and angle from the previous vertex while drawing. See §10.1 for the typed-input grammar.

Shift / Alt while drawing. Each draw tool reads the modifier keys the same way:

Tool	`Shift`	`Alt`
Rect	Constrain to a square	Grow from the center (the click point is the rect's middle, not a corner)
Circle	Polar-lock the radius cursor to a 45° ray (purely a cue — the circle itself is radially symmetric)	—
Arc	Lock the start angle (click 2) and the sweep (click 3) to 45° increments	—
Polygon / Path	Toggle ortho-lock — `Shift` always means "the opposite of the current ortho mode" for that one click	—

Shift+Alt on Rect combines: a square centered on the click. Modifier behavior is consistent with the surrounding ortho/polar settings — F8 (ortho) flips Shift's meaning for Poly/Path/Circle/Arc the same way it always has.

Cancel an in-progress draft any time with Esc, which works mid-drag (Rect / Circle), between vertex clicks (Poly / Path), or between arc phase clicks. Right-click also cancels — except while drawing a polygon, where a right-click instead closes the shape (commits the boundary as drawn, exactly like Enter). Right-clicking with nothing in flight opens the normal context menu.

OSNAP-style helpers (intersection, perpendicular foot, circle center) are always on while drafting and override polar/ortho when within tolerance — they're the most precise hit, so they win.

10.1 Coordinate input grammar (Dynamic Input HUD)

The HUD has two fields: distance (left) and angle (right). Tab swaps focus, Enter commits, Esc cancels. By default the distance field accepts a plain number and uses the live cursor angle, but it ALSO accepts AutoCAD-style coordinate strings — just type them into the distance field:

Syntax	Meaning	Example	Resolves to
`x,y`	Absolute world point in the active display unit	`5,3` (in µm mode)	`(5000, 3000)` nm
`@dx,dy`	Relative offset from the reference point (the previous vertex of the in-progress polyline / drag origin)	`@5,3` after a vertex at `(10,10)`	`(15, 13)`
`@d<θ`	Polar — distance `d` at angle `θ` (degrees CCW from +x) from the reference point	`@5<45`	reference + `(5cos45°, 5sin45°)`

Whitespace is ignored. Decimals are accepted (@2.5,1.5). Negative numbers work (@-5,0 for "5 units to the left"). Distances honour the active display unit (nm / µm / mm — Edit → Settings); angles are unitless degrees regardless.

The HUD picks the parser path automatically: if the string contains any of @, ,, or <, it's treated as a coord. Otherwise it's a plain numeric distance combined with the live cursor angle.

When does the parser run? While drafting any of:

Polygon / Path: each click activates the HUD with the new vertex as the reference point. Type the next vertex's coord and press Enter instead of clicking.
Box / Circle: HUD activates on the first click; the second corner / radius point is what you type.
Stretch translate & Move drags: the current cursor anchor is the reference; type a delta to translate the marked vertices by an exact offset.

Examples:

Drawing a 10 µm × 5 µm rectangle from the origin: click (0,0), then in the HUD type @10,5 and press Enter.
A 30° offset of 12 µm from the previous vertex: type @12<30 and press Enter.
Place a polygon vertex at the absolute point (100, 200) µm: type 100,200 and press Enter.

Parser source: src/canvas/coordParse.ts. Returns { kind: 'absolute' | 'relative' | 'polar' | 'invalid' }; the HUD's resolveCoord step converts to a world-nm point using the active display unit and the reference. Invalid input falls through to the live-angle numeric interpretation, so a typo doesn't cancel your draft — it just commits at the cursor.