private void diagram_LinkCreated(object sender, LinkEventArgs e)
{
	e.Link.Style = LinkStyle.Polyline;
	e.Link.SegmentCount = 2;
	e.Link.CustomDraw = CustomDraw.Full;
}

private void diagram_DrawLink(object sender, DrawLinkEventArgs e)
{
	float x1, y1,              /* beginning point */
	   x2, y2,              /* mid point */
	   x3, y3,              /* ending point */
	   sx1, sx2, sx3,       /* squared x values */
	   sy1, sy2, sy3,       /* squared y values */
	   ad, D, E, F,         /* determinate values */
	   dc, ec, fc,          /* coefficient values */
	   centrex, centrey,    /* centre point of arc */
	   r,                   /* radius of arc */
	   ab, ae;              /* beginning & ending angles */

	x1 = e.Link.ControlPoints[0].X;
	y1 = e.Link.ControlPoints[0].Y;
	x2 = e.Link.ControlPoints[1].X;
	y2 = e.Link.ControlPoints[1].Y;
	x3 = e.Link.ControlPoints[2].X;
	y3 = e.Link.ControlPoints[2].Y;

	/* get squared values */
	sx1 = x1 * x1; sx2 = x2 * x2; sx3 = x3 * x3;
	sy1 = y1 * y1; sy2 = y2 * y2; sy3 = y3 * y3;

	/* get "a" determinate */
	ad = x1 * (y2 - y3) - y1 * (x2 - x3) + x2 * y3 - x3 * y2;

	/* get "D" determinate */
	D = (sx1 + sy1) * (y2 - y3) - y1 * ((sx2 + sy2) - (sx3 + sy3))
		+ y3 * (sx2 + sy2) - y2 * (sx3 + sy3);

	/* get "E" determinate */
	E = (sx1 + sy1) * (x2 - x3) - x1 * ((sx2 + sy2) - (sx3 + sy3))
		+ x3 * (sx2 + sy2) - x2 * (sx3 + sy3);

	/* get "F" determinate */
	F = (sx1 + sy1) * (x2 * y3 - x3 * y2) -
		 x1 * (y3 * (sx2 + sy2) - y2 * (sx3 + sy3)) +
		 y1 * (x3 * (sx2 + sy2) - x2 * (sx3 + sy3));

	D = -D; F = -F;

	/* check for colinear point */
	if (ad == 0.0)
	{
		System.Drawing.Pen lpen = e.Link.Pen.CreateGdiPen();
		e.Graphics.DrawLine(lpen, x1, y1, x3, y3);
		lpen.Dispose();
		return;
	}

	/* get coefficients */
	dc = D / (2.0f * ad);
	ec = E / (2.0f * ad);
	fc = F / ad;

	/* get centre point */
	centrex = -dc; centrey = -ec;

	/* get radius */
	r = (float)Math.Sqrt((dc * dc + ec * ec - fc));

	/* get beginning and ending angles */
	ab = (float)(Math.Atan2(y1 - centrey, x1 - centrex) * 180 / Math.PI);
	ae = (float)(Math.Atan2(y3 - centrey, x3 - centrex) * 180 / Math.PI);

	System.Drawing.Pen pen = e.Link.Pen.CreateGdiPen();
	e.Graphics.DrawArc(pen, centrex - r, centrey - r, r * 2, r * 2, ab, ae - ab);
	pen.Dispose();
}