// https://raytracing.github.io/books/RayTracingTheNextWeek.html#boundingvolumehierarchies
public BvhNode(List <IHittable> srcObjects, int start, int end, AbstractSampler <int> sampler = null)
{
sampler ??= new ThreadSafeSampler <int>(count => IntSampling.Random(count, 0, 3), SAMPLES);
var objects = srcObjects;
int axis = sampler.GetSample();
int Comparator(IHittable a, IHittable b) => BoxCompare(a, b, axis);
int objectSpan = end - start;
switch (objectSpan)
{
case 1:
_left = _right = objects[start];
break;
case 2 when Comparator(objects[start], objects[start + 1]) < 0:
_left = objects[start];
_right = objects[start + 1];
break;
case 2:
_left = objects[start + 1];
_right = objects[start];
break;
default:
objects.Sort(start, objectSpan - 1, new FuncComparer <IHittable>(Comparator));
int mid = start + objectSpan / 2;
_left = new BvhNode(objects, start, mid, sampler);
_right = new BvhNode(objects, mid, end, sampler);
break;
}
var boxLeft = _left.BoundingBox();
var boxRight = _right.BoundingBox();
_box = boxLeft + boxRight;
}
