/* MOUSE HANDLING */
private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
{
if (e.Button == MouseButtons.Left)
{
fig.MousePanStart(e.X, e.Y); // left-click-drag pans
}
else if (e.Button == MouseButtons.Right)
{
fig.MouseZoomStart(e.X, e.Y); // right-click-drag zooms
}
}