Code

private void Expand(PointF center, float scale)
{
	foreach (DiagramNode node in diagram.Nodes)
	{
		PointF nodePos = node.GetCenter();
		PointF newPos = new PointF(
			center.X + (nodePos.X - center.X) * scale,
			center.Y + (nodePos.Y - center.Y) * scale);
		node.Bounds = RectangleF.FromLTRB(
			newPos.X - node.Bounds.Width / 2,
			newPos.Y - node.Bounds.Height / 2,
			newPos.X + node.Bounds.Width / 2,
			newPos.Y + node.Bounds.Height / 2);
	}
}