PinchCommand.cs

        private void PinchGesturePinchUpdated(object sender, PinchGestureUpdatedEventArgs e)
        {
            if(e.Status == GestureStatus.Started)
            {
                AmbientControl = AmbientControl.Zoom;
                StartCanvasScale = CanvasScale;
            }
            else if(e.Status == GestureStatus.Running)
            {
                var factor = (e.Scale - 1);
                var delta = factor < 0 ? -1 : 1;

                factor = (factor * delta).Clamp(0, MaximumZoomStep) * delta;
                
                CanvasScale += ((factor * StartCanvasScale)).ToSingle();
                CanvasScale = CanvasScale.Clamp(0.01f, 2);

                if(delta > 0)
                {
                    var touchX = (WidthScreen * e.ScaleOrigin.X).ToSingle();
                    var touchY = (HeightScreen * e.ScaleOrigin.Y).ToSingle();
                    var centerXScreen = WidthScreen / 2;
                    var centerYScreen = HeightScreen / 2;
                    
                    CanvasPosition.X += (centerXScreen - touchX) * CanvasScale;
                    CanvasPosition.Y += (centerYScreen - touchY) * CanvasScale;
                }
                else
                {
                    var centerXScreen = (WidthScreen / 2);
                    var centerYScreen = (HeightScreen / 2);

                    var newCenterXScreen = (WidthScreen * ((factor * StartCanvasScale))) / 2;
                    var newCenterYScreen = (HeightScreen * ((factor * StartCanvasScale))) / 2;

                    CanvasPosition.X += (newCenterXScreen - centerXScreen).ToSingle();
                    CanvasPosition.Y += (newCenterYScreen - centerYScreen).ToSingle();
                }

                CanvasView.InvalidateSurface();
                StartCanvasScale = CanvasScale;
            }
            else
            {
                AmbientControl = AmbientControl.Stoped;
            }
        }