@ue-too/board / index / TouchInputTracker

Class: TouchInputTracker

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:99

Production implementation of TouchContext that tracks multi-touch state.

Remarks

This class maintains a map of active touch points, storing their initial positions to enable gesture recognition. The state machine uses this context to:

• Calculate pan deltas (difference between initial and current midpoint)
• Calculate zoom factors (change in distance between two touch points)
• Determine gesture type (pan vs zoom based on relative magnitudes)

Touch Point Lifecycle:

1. addTouchPoints: Called on touchstart to register new touches
2. updateTouchPoints: Called on touchmove to update current positions
3. removeTouchPoints: Called on touchend/touchcancel to unregister touches

The initial positions are preserved until the touch ends, allowing continuous calculation of deltas throughout the gesture.

Example

const canvasProxy = new CanvasProxy(canvasElement);
const context = new TouchInputTracker(canvasProxy);
const stateMachine = createTouchInputStateMachine(context);

// When a two-finger touch starts
context.addTouchPoints([
  {ident: 0, x: 100, y: 200},
  {ident: 1, x: 300, y: 200}
]);
console.log(context.getCurrentTouchPointsCount()); // 2

Implements

• TouchContext

Constructors

Constructor

new TouchInputTracker(canvas): TouchInputTracker

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:107

Parameters

canvas

Canvas

Returns

TouchInputTracker

Accessors

alignCoordinateSystem

Get Signature

get alignCoordinateSystem(): boolean

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:151

Whether to use standard screen coordinate system (vs inverted Y-axis)

Returns

boolean

Set Signature

set alignCoordinateSystem(value): void

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:155

Whether to use standard screen coordinate system (vs inverted Y-axis)

Parameters

value

boolean

Returns

void

Whether to use standard screen coordinate system (vs inverted Y-axis)

Implementation of

TouchContext.alignCoordinateSystem

---

canvas

Get Signature

get canvas(): Canvas

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:159

Canvas accessor for dimensions and coordinate transformations

Returns

Canvas

Canvas accessor for dimensions and coordinate transformations

Implementation of

TouchContext.canvas

Methods

addTouchPoints()

addTouchPoints(points): void

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:112

Adds new touch points to tracking

Parameters

points

TouchPoints[]

Returns

void

Implementation of

TouchContext.addTouchPoints

---

cleanup()

cleanup(): void

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:163

Returns

void

Implementation of

TouchContext.cleanup

---

getCurrentTouchPointsCount()

getCurrentTouchPointsCount(): number

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:126

Returns the current number of active touch points

Returns

number

Implementation of

TouchContext.getCurrentTouchPointsCount

---

getInitialTouchPointsPositions()

getInitialTouchPointsPositions(idents): TouchPoints[]

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:130

Retrieves the initial positions of specific touch points

Parameters

idents

number[]

Returns

TouchPoints[]

Implementation of

TouchContext.getInitialTouchPointsPositions

---

removeTouchPoints()

removeTouchPoints(identifiers): void

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:118

Removes touch points from tracking by identifier

Parameters

identifiers

number[]

Returns

void

Implementation of

TouchContext.removeTouchPoints

---

setup()

setup(): void

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:165

Returns

void

Implementation of

TouchContext.setup

---

updateTouchPoints()

updateTouchPoints(pointsMoved): void

Defined in: packages/board/src/input-interpretation/input-state-machine/touch-input-context.ts:143

Updates the current positions of touch points

Parameters

pointsMoved

TouchPoints[]

Returns

void

Implementation of

TouchContext.updateTouchPoints