private void panel_MouseUp(object sender, MouseEventArgs e)
{
var diem = new Diem()
{
Location = new Point(e.Location.X, e.Location.Y), Color = Color.Blue,
};
if (!OverLap(diem))
{
doThi.ThemDinh(diem);
this.panel.Controls.Add(diem);
doThi.OnGraphChanged -= doThi_OnGraphChanged;
doThi.OnGraphChanged += doThi_OnGraphChanged;
}
}