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). Enter commits, Esc cancels. Tab/Shift+Tab move focus forward/backward between the two fields like any ordinary input pair — Tab from Distance goes to Angle and Shift+Tab from Angle goes back to Distance, but Shift+Tab on Distance and Tab on Angle leave the HUD entirely (there's nothing before the first field or after the last one) rather than bouncing back and forth. 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.

Keyboard-only start (no click at all). With Box, Circle, Polygon, or Path armed and nothing drawn yet, press Enter instead of clicking: it opens the HUD to type the FIRST anchor as an absolute point (plain x,y — the reference point is meaningless before anything exists to measure from), auto-focused so you can start typing immediately, and submitting it starts the draft exactly as if you'd clicked there. Every later vertex/corner works the same as the click-started flow above. This is the only way to draw a shape with no pointing device at all; Esc from this first-anchor HUD closes it with nothing drawn (there's no in-progress gesture yet to fall back to).

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.