The samples can now be scaled and panned. Closes #173

samples/FormsSample/Core/DetailContentsPage.xaml

@@ -7,11 +7,15 @@
     <views:SKCanvasView x:Name="canvas" PaintSurface="OnPaintSample">
       <views:SKCanvasView.GestureRecognizers>
         <TapGestureRecognizer Tapped="OnTapSample" />
+        <PanGestureRecognizer PanUpdated="OnPanSample" />
+        <PinchGestureRecognizer PinchUpdated="OnPinchSample" />
       </views:SKCanvasView.GestureRecognizers>
     </views:SKCanvasView>
     <views:SKGLView x:Name="glview" PaintSurface="OnPaintGLSample" IsVisible="False" HasRenderLoop="False">
       <views:SKGLView.GestureRecognizers>
         <TapGestureRecognizer Tapped="OnTapSample" />
+        <PanGestureRecognizer PanUpdated="OnPanSample" />
+        <PinchGestureRecognizer PinchUpdated="OnPinchSample" />
       </views:SKGLView.GestureRecognizers>
     </views:SKGLView>
   </Grid>

samples/FormsSample/Core/DetailContentsPage.xaml.cs

@@ -58,6 +58,31 @@ namespace SkiaSharpSample.FormsSample
 			Sample?.Tap();
 		}
 
+		private void OnPanSample(object sender, PanUpdatedEventArgs e)
+		{
+			var scale = canvas.CanvasSize.Width / (float)canvas.Width;
+			if (glview.IsVisible)
+				scale = glview.CanvasSize.Width / (float)glview.Width;
+			
+			Sample?.Pan(
+				(GestureState)(int)e.StatusType,
+				new SKPoint((float)e.TotalX * scale, (float)e.TotalY * scale));
+			RefreshSamples();
+		}
+
+		private void OnPinchSample(object sender, PinchGestureUpdatedEventArgs e)
+		{
+			var size = canvas.CanvasSize;
+			if (glview.IsVisible)
+				size = glview.CanvasSize;
+
+			Sample?.Pinch(
+				(GestureState)(int)e.Status,
+				(float)e.Scale,
+				new SKPoint((float)e.ScaleOrigin.X * size.Width, (float)e.ScaleOrigin.Y * size.Height));
+			RefreshSamples();
+		}
+
 		private void OnPaintSample(object sender, SKPaintSurfaceEventArgs e)
 		{
 			Sample?.DrawSample(e.Surface.Canvas, e.Info.Width, e.Info.Height);

samples/SkiaSharpSample.Shared/SampleBase.cs

@@ -6,6 +6,13 @@ namespace SkiaSharpSample
 {
 	public abstract class SampleBase
 	{
+		protected SKMatrix Matrix = SKMatrix.MakeIdentity();
+
+		private SKMatrix startPanMatrix = SKMatrix.MakeIdentity();
+		private SKMatrix startPinchMatrix = SKMatrix.MakeIdentity();
+		private SKPoint startPinchOrigin = SKPoint.Empty;
+		private float totalPinchScale = 1f;
+
 		public abstract string Title { get; }
 
 		public virtual string Description { get; } = string.Empty;
@@ -22,6 +29,7 @@ namespace SkiaSharpSample
 		{
 			if (IsInitialized)
 			{
+				canvas.SetMatrix(Matrix);
 				OnDrawSample(canvas, width, height);
 			}
 		}
@@ -30,6 +38,9 @@ namespace SkiaSharpSample
 
 		public async void Init(Action callback = null)
 		{
+			// reset the matrix for the new sample
+			Matrix = SKMatrix.MakeIdentity();
+
 			if (!IsInitialized)
 			{
 				await OnInit();
@@ -57,6 +68,49 @@ namespace SkiaSharpSample
 		{
 		}
 
+		public void Pan(GestureState state, SKPoint translation)
+		{
+			switch (state)
+			{
+				case GestureState.Started:
+					startPanMatrix = Matrix;
+					break;
+				case GestureState.Running:
+					var canvasTranslation = SKMatrix.MakeTranslation(translation.X, translation.Y);
+					SKMatrix.Concat(ref Matrix, ref canvasTranslation, ref startPanMatrix);
+					break;
+				default:
+					startPanMatrix = SKMatrix.MakeIdentity();
+					break;
+			}
+		}
+
+		public void Pinch(GestureState state, float scale, SKPoint origin)
+		{
+			switch (state)
+			{
+				case GestureState.Started:
+					startPinchMatrix = Matrix;
+					startPinchOrigin = origin;
+					totalPinchScale = 1f;
+					break;
+				case GestureState.Running:
+					totalPinchScale *= scale;
+					var pinchTranslation = origin - startPinchOrigin;
+					var canvasTranslation = SKMatrix.MakeTranslation(pinchTranslation.X, pinchTranslation.Y);
+					var canvasScaling = SKMatrix.MakeScale(totalPinchScale, totalPinchScale, origin.X, origin.Y);
+					var canvasCombined = SKMatrix.MakeIdentity();
+					SKMatrix.Concat(ref canvasCombined, ref canvasScaling, ref canvasTranslation);
+					SKMatrix.Concat(ref Matrix, ref canvasCombined, ref startPinchMatrix);
+					break;
+				default:
+					startPinchMatrix = SKMatrix.MakeIdentity();
+					startPinchOrigin = SKPoint.Empty;
+					totalPinchScale = 1f;
+					break;
+			}
+		}
+
 		public virtual bool MatchesFilter(string searchText)
 		{
 			if (string.IsNullOrWhiteSpace(searchText))
@@ -67,4 +121,12 @@ namespace SkiaSharpSample
 				Description.IndexOf(searchText, StringComparison.OrdinalIgnoreCase) != -1;
 		}
 	}
+
+	public enum GestureState
+	{
+		Started,
+		Running,
+		Completed,
+		Canceled
+	}
 }