void OnSliderValueChanged(object sender, RoutedPropertyChangedEventArgs <double> e)
{
ImageScaleTransform.ScaleX = e.NewValue;
ImageScaleTransform.ScaleY = e.NewValue;
var centerOfViewport = new Point(ImageScrollViewer.ViewportWidth / 2, ImageScrollViewer.ViewportHeight / 2);
_lastCenterPositionOnTarget = ImageScrollViewer.TranslatePoint(centerOfViewport, ImageGrid);
}
void OnScrollViewerScrollChanged(object sender, ScrollChangedEventArgs e)
{
if (e.ExtentHeightChange != 0 || e.ExtentWidthChange != 0)
{
Point?targetBefore = null;
Point?targetNow = null;
if (!_lastMousePositionOnTarget.HasValue)
{
if (_lastCenterPositionOnTarget.HasValue)
{
var centerOfViewport = new Point(ImageScrollViewer.ViewportWidth / 2, ImageScrollViewer.ViewportHeight / 2);
var centerOfTargetNow = ImageScrollViewer.TranslatePoint(centerOfViewport, ImageGrid);
targetBefore = _lastCenterPositionOnTarget;
targetNow = centerOfTargetNow;
}
}
else
{
targetBefore = _lastMousePositionOnTarget;
targetNow = Mouse.GetPosition(ImageGrid);
_lastMousePositionOnTarget = null;
}
if (targetBefore.HasValue)
{
var dXInTargetPixels = targetNow.Value.X - targetBefore.Value.X;
var dYInTargetPixels = targetNow.Value.Y - targetBefore.Value.Y;
var multiplicatorX = e.ExtentWidth / ImageGrid.Width;
var multiplicatorY = e.ExtentHeight / ImageGrid.Height;
var newOffsetX = ImageScrollViewer.HorizontalOffset - dXInTargetPixels * multiplicatorX;
var newOffsetY = ImageScrollViewer.VerticalOffset - dYInTargetPixels * multiplicatorY;
if (double.IsNaN(newOffsetX) || double.IsNaN(newOffsetY))
{
return;
}
ImageScrollViewer.ScrollToHorizontalOffset(newOffsetX);
ImageScrollViewer.ScrollToVerticalOffset(newOffsetY);
}
}
}