fix: lock pinch zoom pivot when pan is disabled

When IsPanEnabled is false, the pinch focal point is now fixed to where
the gesture started, preventing effective panning through zoom+move.
The _pinchFocalPointOverride field is cleared when the gesture ends.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mattleibow

source/SkiaSharp.Extended/Gestures/SKGestureTracker.cs

@@ -72,6 +72,7 @@ public sealed class SKGestureTracker : IDisposable
 	private float _zoomTargetFactor;
 	private SKPoint _zoomFocalPoint;
 	private long _zoomStartTicks;
+	private SKPoint? _pinchFocalPointOverride;
 
 	/// <summary>
 	/// Initializes a new instance of the <see cref="SKGestureTracker"/> class with default options.
@@ -683,8 +684,16 @@ private void OnEnginePinchDetected(object? s, SKPinchGestureEventArgs e)
 
 		if (IsPinchEnabled)
 		{
+			// When pan is disabled, lock the zoom pivot to where the pinch started
+			// so that moving fingers during a pinch doesn't cause effective panning.
+			if (!IsPanEnabled)
+				_pinchFocalPointOverride ??= e.FocalPoint;
+			else
+				_pinchFocalPointOverride = null;
+
+			var pivot = _pinchFocalPointOverride ?? e.FocalPoint;
 			var newScale = Clamp(_scale * e.ScaleDelta, Options.MinScale, Options.MaxScale);
-			AdjustOffsetForPivot(e.FocalPoint, _scale, newScale, _rotation, _rotation);
+			AdjustOffsetForPivot(pivot, _scale, newScale, _rotation, _rotation);
 			_scale = newScale;
 		}
 
@@ -749,6 +758,8 @@ private void OnEngineGestureStarted(object? s, SKGestureLifecycleEventArgs e)
 
 	private void OnEngineGestureEnded(object? s, SKGestureLifecycleEventArgs e)
 	{
+		_pinchFocalPointOverride = null;
+
 		if (_isDragging)
 		{
 			_isDragging = false;

tests/SkiaSharp.Extended.Tests/Gestures/SKGestureTrackerTests.cs

@@ -1152,5 +1152,33 @@ public void SetScaleRange_NegativeMin_Throws()
 		var options = new SKGestureTrackerOptions();
 		Assert.Throws<ArgumentOutOfRangeException>(() => options.SetScaleRange(-1f, 10f));
 	}
+	[Fact]
+	public void PinchWithPanDisabled_FingersTranslate_OffsetDoesNotChange()
+	{
+		// Bug fix: when IsPanEnabled=false, moving the finger midpoint during a pinch
+		// (translation, no scale change) should not cause the content to pan.
+		var tracker = CreateTracker();
+		tracker.IsPanEnabled = false;
+		tracker.IsPinchEnabled = true;
+		tracker.IsRotateEnabled = false; // isolate pinch-only behavior
+
+		var initialOffset = tracker.Offset;
+
+		// Both fingers go down 100px apart
+		tracker.ProcessTouchDown(1, new SKPoint(150, 200));
+		tracker.ProcessTouchDown(2, new SKPoint(250, 200));
+
+		// Both fingers translate upward together (same distance = scale delta 1.0)
+		tracker.ProcessTouchMove(1, new SKPoint(150, 100));
+		tracker.ProcessTouchMove(2, new SKPoint(250, 100));
+
+		// Translate further
+		tracker.ProcessTouchMove(1, new SKPoint(150, 50));
+		tracker.ProcessTouchMove(2, new SKPoint(250, 50));
+
+		// Offset must not change -- pure translation with pan disabled should be ignored
+		Assert.Equal(initialOffset.X, tracker.Offset.X, 1f);
+		Assert.Equal(initialOffset.Y, tracker.Offset.Y, 1f);
+	}
 
 }