private static void CheckCircle(RBTreeNode <BeachSection> section, MinHeap <FortuneEvent> eventQueue)
{
//if (section == null)
// return;
var left = section.Previous;
var right = section.Next;
if (left == null || right == null)
{
return;
}
var leftSite = left.Data.Site;
var centerSite = section.Data.Site;
var rightSite = right.Data.Site;
//if the left arc and right arc are defined by the same
//focus, the two arcs cannot converge
if (leftSite == rightSite)
{
return;
}
// http://mathforum.org/library/drmath/view/55002.html
// because every piece of this program needs to be demoed in maple >.<
//MATH HACKS: place center at origin and
//draw vectors a and c to
//left and right respectively
float bx = centerSite.X,
by = centerSite.Y,
ax = leftSite.X - bx,
ay = leftSite.Y - by,
cx = rightSite.X - bx,
cy = rightSite.Y - by;
//The center beach section can only dissapear when
//the angle between a and c is negative
var d = ax * cy - ay * cx;
if (d.ApproxGreaterThanOrEqualTo(0))
{
return;
}
var magnitudeA = ax * ax + ay * ay;
var magnitudeC = cx * cx + cy * cy;
var x = (cy * magnitudeA - ay * magnitudeC) / (2 * d);
var y = (ax * magnitudeC - cx * magnitudeA) / (2 * d);
//add back offset
var ycenter = y + by;
//y center is off
var circleEvent = new FortuneCircleEvent(
new VPoint(x + bx, ycenter + (float)Math.Sqrt(x * x + y * y)),
ycenter, section
);
section.Data.CircleEvent = circleEvent;
eventQueue.Insert(circleEvent);
}
