Class SKGestureTracker

Namespace: SkiaSharp.Extended

Assembly: SkiaSharp.Extended.dll

A high-level gesture handler that recognizes touch gestures and maintains an absolute transform (scale, rotation, and offset).

public sealed class SKGestureTracker : IDisposable

Inheritance: object

SKGestureTracker

Implements: IDisposable

Inherited Members: object.GetType()

object.ToString()

object.Equals(object)

object.Equals(object, object)

object.ReferenceEquals(object, object)

object.GetHashCode()

Remarks

The tracker is the primary public API for gesture handling. It accepts raw touch input via ProcessTouchDown(long, SKPoint, bool), ProcessTouchMove(long, SKPoint, bool), ProcessTouchUp(long, SKPoint), and ProcessMouseWheel(SKPoint, float, float), detects gestures internally, and translates them into transform state changes and higher-level events such as drag lifecycle and fling animation.

Use the Matrix property to apply the current transform when painting. The matrix uses (0,0) as its origin — no view size configuration is required.

All coordinates are in view (screen) space. The tracker converts screen-space deltas to content-space deltas internally when updating Offset.

Basic usage with an SkiaSharp canvas:

var tracker = new SKGestureTracker();
// Forward touch events from your platform:
tracker.ProcessTouchDown(id, new SKPoint(x, y));
tracker.ProcessTouchMove(id, new SKPoint(x, y));
tracker.ProcessTouchUp(id, new SKPoint(x, y));
// In your paint handler:
canvas.Save();
canvas.Concat(tracker.Matrix);
// Draw your content...
canvas.Restore();
// Listen for transform changes to trigger redraws:
tracker.TransformChanged += (s, e) => canvasView.InvalidateSurface();

SKGestureTrackerOptions

Constructors

SKGestureTracker(): Initializes a new instance of the SKGestureTracker class with default options.

SKGestureTracker(SKGestureTrackerOptions): Initializes a new instance of the SKGestureTracker class with the specified options.

Properties

IsDoubleTapEnabled: Gets or sets a value indicating whether double-tap detection is enabled.

IsDoubleTapZoomEnabled: Gets or sets a value indicating whether double-tap triggers an animated zoom.

IsEnabled: Gets or sets a value indicating whether gesture detection is enabled.

IsFlingEnabled: Gets or sets a value indicating whether fling (inertia) animation is enabled after a pan gesture.

IsFlinging: Gets a value indicating whether a fling (inertia) animation is in progress.

IsGestureActive: Gets a value indicating whether any gesture is currently active (touch contact in progress).

IsHoverEnabled: Gets or sets a value indicating whether hover (mouse move without contact) detection is enabled.

IsLongPressEnabled: Gets or sets a value indicating whether long press detection is enabled.

IsPanEnabled: Gets or sets a value indicating whether pan gestures update the Offset.

IsPinchEnabled: Gets or sets a value indicating whether pinch-to-zoom gestures update the Scale.

IsRotateEnabled: Gets or sets a value indicating whether rotation gestures update the Rotation.

IsScrollZoomEnabled: Gets or sets a value indicating whether scroll-wheel events trigger zoom.

IsTapEnabled: Gets or sets a value indicating whether tap detection is enabled.

IsZoomAnimating: Gets a value indicating whether an animated zoom (from double-tap or ZoomTo(float, SKPoint)) is in progress.

Matrix: Gets the composite transform matrix that combines scale, rotation, and offset, using (0,0) as the transform origin.

Offset: Gets the current pan offset in content coordinates.

Options: Gets the configuration options for this tracker.

Rotation: Gets the current rotation angle in degrees.

Scale: Gets the current zoom scale factor.

Methods

Dispose(): Releases all resources used by this SKGestureTracker instance, including stopping all animations.

ProcessMouseWheel(SKPoint, float, float): Processes a mouse wheel (scroll) event.

ProcessTouchCancel(long): Processes a touch cancel event.

ProcessTouchDown(long, SKPoint, bool): Processes a touch down event.

ProcessTouchMove(long, SKPoint, bool): Processes a touch move event.

ProcessTouchUp(long, SKPoint): Processes a touch up event.

Reset(): Resets the tracker to an identity transform (scale 1, rotation 0, offset zero), stops all animations, and raises TransformChanged.

SetOffset(SKPoint): Sets the pan offset and raises TransformChanged.

SetRotation(float, SKPoint?): Sets the rotation angle and raises TransformChanged.

SetScale(float, SKPoint?): Sets the zoom scale, clamping to MinScale/MaxScale, and raises TransformChanged.

SetTransform(float, float, SKPoint): Sets the transform to the specified values, clamping scale to MinScale/MaxScale.

StopFling(): Stops any active fling animation and raises FlingCompleted.

StopZoomAnimation(): Stops any active zoom animation immediately.

ZoomTo(float, SKPoint): Starts an animated zoom by the given multiplicative factor around a focal point.

Events

DoubleTapDetected: Occurs when a double tap is detected.

DragEnded: Occurs when a drag operation ends (all touches released).

DragStarted: Occurs when a drag operation starts (first pan movement after touch down).

DragUpdated: Occurs on each movement during a drag operation.

FlingCompleted: Occurs when a fling animation completes (velocity drops below FlingMinVelocity).

FlingDetected: Occurs when a fling gesture is detected (once, with initial velocity).

FlingUpdated: Occurs each animation frame during a fling deceleration.

GestureEnded: Occurs when a gesture interaction ends (last touch released).

GestureStarted: Occurs when a gesture interaction begins (first touch contact).

HoverDetected: Occurs when a hover is detected.

LongPressDetected: Occurs when a long press is detected.

PanDetected: Occurs when a pan gesture is detected.

PinchDetected: Occurs when a pinch (scale) gesture is detected.

RotateDetected: Occurs when a rotation gesture is detected.

ScrollDetected: Occurs when a scroll (mouse wheel) event is detected.

TapDetected: Occurs when a single tap is detected.