public void RemoveViewport(ShadowVisual shadowViewport)
{
shadowViewport.ViewportChanged -= Raw_ViewportChanged;
_viewports.Remove(shadowViewport.Visual);
ViewportRemoved?.Invoke(this, new ShadowViewportEventArgs(shadowViewport));
// update viewport count on hosting monitor
ShadowMonitor monitor = _monitors[shadowViewport.Monitor];
monitor.RemoveViewport();
// recalculate, delayed
ScheduleGeometryChange();
}
