public BVHNode Construct(BVHNode leaf)
{
if (leaf.Boundables.Count == 0)
{
return(leaf);
}
var bb = BoundingBox.FromBoundables(leaf.Boundables);
var xLen = bb.Max.X - bb.Min.X;
var yLen = bb.Max.Y - bb.Min.Y;
var zLen = bb.Max.Z - bb.Min.Z;
List <Boundable> sorted;
if (xLen > yLen && xLen > zLen)
{
sorted = leaf.Boundables.OrderBy(x => x.BoundingBox.Centroid.X).ToList();
}
else if (yLen > xLen && yLen > zLen)
{
sorted = leaf.Boundables.OrderBy(x => x.BoundingBox.Centroid.Y).ToList();
}
else
{
sorted = leaf.Boundables.OrderBy(x => x.BoundingBox.Centroid.Z).ToList();
}
var bestPlane = CalculateBestSplitPlane(sorted);
//don't split further
if (bestPlane.Cost > leaf.BoundingBox.Area * leaf.Boundables.Count)
{
return(leaf);
}
var left = new BVHNode(bestPlane.Left);
var right = new BVHNode(bestPlane.Right);
var parent = new BVHNode(Construct(left), Construct(right));
return(parent);
}
private SplitPlane CalculateBestSplitPlane(List <Boundable> boundables)
{
var bestSplitPlane = new SplitPlane(float.MaxValue, null, null);
for (int i = 1; i < boundables.Count; i++)
{
var left = boundables.Take(i).ToList();
var leftB = BoundingBox.FromBoundables(left);
var right = boundables.Skip(i).ToList();
var rightB = BoundingBox.FromBoundables(right);
var cost = leftB.Area * left.Count + rightB.Area * right.Count;
if (cost < bestSplitPlane.Cost)
{
bestSplitPlane = new SplitPlane(cost, left, right);
}
}
return(bestSplitPlane);
}