public bool ShowVisibility(bool randomize)
{
// find all nodes visible from source node
T source = FindSource(randomize);
var visibility = new Visibility <T>(Graph);
visibility.Threshold = (double)Dialog.ThresholdUpDown.Value;
Predicate <T> isOpaque = p => NodeCosts[p] >= MaxCost;
bool success = visibility.FindVisible(isOpaque, source);
Locations = visibility.Nodes;
Renderer.InvalidateVisual();
return(success);
}