/**
* Recursive version of ClipOutTriangles. This method partitions the triangles
* in @triangles using @node's split plane, and then recursively calls itself
* with the resulting greater-than and less-than lists. If the recursion reaches a
* point where triangles in @triangles are on the back side of @node's split plane,
* but this instance of BSPTree contains no geometry on that side (node.LessThan == null),
* then the triangles placed in @lessThan are deleted from @triangles. This removes
* the portions of triangles in @triangles that lie inside the geometry of this BSPTree
* instance.
*
* If @clippLessThan is false, then we perform the reverse of the above oepration.
* Triangles placed in @greaterThan than are removed when node.GreaterThan == null.
* In that case the portions of triangles in @triangles that lie outside the geometry
* of this BSPTree instance are removed.
*/
private void ClipOutTriangles(Node node, FastLinkedList <Triangle> triangles, bool clipLessThan = true, IList <Triangle> discarded = null)
{
if (triangles == null || triangles.First == null)
{
return;
}
if (node == null)
{
return;
}
FastLinkedList <Triangle> lessThan = new FastLinkedList <Triangle>();
FastLinkedList <Triangle> greaterThan = new FastLinkedList <Triangle>();
// iterate through each triangle in @triangles and classify/partition each according
// @node's split plane. triangles on the front side go into @greaterThan, triangles
// on the back side go into @lessThan. co-planar triangles whose normal matches that of
// @node's split plane go into @greaterThan; the rest go into @lessThan.
triangles.Iterate((Triangle tri) => {
Partitioner.Orientation orient = Partitioner.SliceTriangle(tri, node.SplitPlane, lessThan, greaterThan, lessThan, greaterThan, true);
});
// release memory used by @triangles
triangles.Clear();
// recurse on the back side of @node's split plane if this BSPTree contains
// geometry on that side. if it does not, and we want to clip out triangles
// inside this BSPTree's geometry (@clipLessThan == true), then we clear out @lessThan.
if (node.LessThan != null)
{
ClipOutTriangles(node.LessThan, lessThan, clipLessThan, discarded);
}
else if (clipLessThan)
{
if (discarded != null)
{
lessThan.CopyInto(discarded);
}
lessThan.Clear();
}
// recurse on the front side of @node's split plane if this BSPTree contains
// geometry on that side. if it does not, and we want to clip out triangles
// outside this BSPTree's geometry (@clipLessThan == false), then we clear out @greaterThan.
if (node.GreaterThan != null)
{
ClipOutTriangles(node.GreaterThan, greaterThan, clipLessThan, discarded);
}
else if (!clipLessThan)
{
if (discarded != null)
{
greaterThan.CopyInto(discarded);
}
greaterThan.Clear();
}
// rebuild @triangles with the properly clipped triangles
triangles.AppendIntoList(lessThan);
triangles.AppendIntoList(greaterThan);
}