private void scrollViewerPreviewMouseWheel(object sender, MouseWheelEventArgs e)
{
System.Windows.Point mouseAtImage = e.GetPosition(viewport);
System.Windows.Point mouseAtScrollViewer = e.GetPosition(scrollViewer);
ScaleTransform st = viewport.LayoutTransform as ScaleTransform;
if (st == null)
{
st = new ScaleTransform();
viewport.LayoutTransform = st;
}
if (e.Delta > 0)
{
st.ScaleX = st.ScaleY = st.ScaleX * 1.25;
if (st.ScaleX > 64)
{
st.ScaleX = st.ScaleY = 64;
}
}
else
{
st.ScaleX = st.ScaleY = st.ScaleX / 1.25;
if (st.ScaleX < 1)
{
st.ScaleX = st.ScaleY = 1;
}
}
#region [this step is critical for offset]
scrollViewer.ScrollToHorizontalOffset(0);
scrollViewer.ScrollToVerticalOffset(0);
window.UpdateLayout();
#endregion
Vector offset = viewport.TranslatePoint(mouseAtImage, scrollViewer) - mouseAtScrollViewer;
scrollViewer.ScrollToHorizontalOffset(offset.X);
scrollViewer.ScrollToVerticalOffset(offset.Y);
window.UpdateLayout();
e.Handled = true;
}
