+void Painter::DrawArrowhead(Vector head, Vector tail)
+{
+ QPolygonF arrow;
+
+ // We draw the arrowhead aligned along the line from tail to head
+ double angle = Vector(head - tail).Angle();
+ double orthoAngle = angle + (PI / 2.0);
+ Vector orthogonal = Vector(cos(orthoAngle), sin(orthoAngle));
+ Vector unit = Vector(head - tail).Unit();
+
+// NOTE: SCREEN_ZOOM is a kludge to make things look right at scale...
+ Point p1 = head - (unit * 9.0 * SCREEN_ZOOM);
+ Point p2 = p1 + (orthogonal * 3.0 * SCREEN_ZOOM);
+ Point p3 = p1 - (orthogonal * 3.0 * SCREEN_ZOOM);
+
+ Point p4 = CartesianToQtCoords(head);
+ Point p5 = CartesianToQtCoords(p2);
+ Point p6 = CartesianToQtCoords(p3);
+
+ arrow << QPointF(p4.x, p4.y) << QPointF(p5.x, p5.y) << QPointF(p6.x, p6.y);
+
+ painter->drawPolygon(arrow);
+}
+