private int AllocateNode()
{
// Expand the node pool as needed.
if (_freeList == NullNode)
{
Debug.Assert(_nodeCount == _nodeCapacity);
// The free list is empty. Rebuild a bigger pool.
DynamicTreeNode[] oldNodes = _nodes;
_nodeCapacity *= 2;
_nodes = new DynamicTreeNode[_nodeCapacity];
Array.Copy(oldNodes, _nodes, _nodeCount);
// Build a linked list for the free list. The parent
// pointer becomes the "next" pointer.
for (int i = _nodeCount; i < _nodeCapacity - 1; ++i)
{
_nodes[i].parentOrNext = i + 1;
}
_nodes[_nodeCapacity - 1].parentOrNext = NullNode;
_freeList = _nodeCount;
}
// Peel a node off the free list.
int nodeId = _freeList;
_freeList = _nodes[nodeId].parentOrNext;
_nodes[nodeId].parentOrNext = NullNode;
_nodes[nodeId].child1 = NullNode;
_nodes[nodeId].child2 = NullNode;
++_nodeCount;
return(nodeId);
}
/// Query an AABB for overlapping proxies. The callback class
/// is called for each proxy that overlaps the supplied AABB.
public void Query(Action <int> callback, ref AABB aabb)
{
int count = 0;
stack[count++] = _root;
while (count > 0)
{
int nodeId = stack[--count];
if (nodeId == NullNode)
{
continue;
}
DynamicTreeNode node = _nodes[nodeId];
if (AABB.TestOverlap(ref node.aabb, ref aabb))
{
if (node.IsLeaf())
{
callback(node.userData);
}
else
{
Debug.Assert(count + 1 < k_stackSize);
stack[count++] = node.child1;
stack[count++] = node.child2;
}
}
}
}
private int ComputeHeight(int nodeId)
{
if (nodeId == NullNode)
{
return(0);
}
Debug.Assert(0 <= nodeId && nodeId < _nodeCapacity);
DynamicTreeNode node = _nodes[nodeId];
int height1 = ComputeHeight(node.child1);
int height2 = ComputeHeight(node.child2);
return(1 + Math.Max(height1, height2));
}
/// ructing the tree initializes the node pool.
public DynamicTree()
{
_root = NullNode;
_nodeCapacity = 16;
_nodeCount = 0;
_nodes = new DynamicTreeNode[_nodeCapacity];
// Build a linked list for the free list.
for (int i = 0; i < _nodeCapacity - 1; ++i)
{
_nodes[i].parentOrNext = i + 1;
}
_nodes[_nodeCapacity - 1].parentOrNext = NullNode;
_freeList = 0;
_path = 0;
}
/// Ray-cast against the proxies in the tree. This relies on the callback
/// to perform a exact ray-cast in the case were the proxy contains a shape.
/// The callback also performs the any collision filtering. This has performance
/// roughly equal to k * log(n), where k is the number of collisions and n is the
/// number of proxies in the tree.
/// @param input the ray-cast input data. The ray extends from p1 to p1 + maxFraction * (p2 - p1).
/// @param callback a callback class that is called for each proxy that is hit by the ray.
public void RayCast(RayCastCallback callback, ref RayCastInput input)
{
Vector2 p1 = input.p1;
Vector2 p2 = input.p2;
Vector2 r = p2 - p1;
Debug.Assert(r.LengthSquared() > 0.0f);
r.Normalize();
// v is perpendicular to the segment.
Vector2 v = MathUtils.Cross(1.0f, r);
Vector2 abs_v = MathUtils.Abs(v);
// Separating axis for segment (Gino, p80).
// |dot(v, p1 - c)| > dot(|v|, h)
float maxFraction = input.maxFraction;
// Build a bounding box for the segment.
AABB segmentAABB = new AABB();
{
Vector2 t = p1 + maxFraction * (p2 - p1);
segmentAABB.lowerBound = Vector2.Min(p1, t);
segmentAABB.upperBound = Vector2.Max(p1, t);
}
int count = 0;
stack[count++] = _root;
while (count > 0)
{
int nodeId = stack[--count];
if (nodeId == NullNode)
{
continue;
}
DynamicTreeNode node = _nodes[nodeId];
if (AABB.TestOverlap(ref node.aabb, ref segmentAABB) == false)
{
continue;
}
// Separating axis for segment (Gino, p80).
// |dot(v, p1 - c)| > dot(|v|, h)
Vector2 c = node.aabb.GetCenter();
Vector2 h = node.aabb.GetExtents();
float separation = Math.Abs(Vector2.Dot(v, p1 - c)) - Vector2.Dot(abs_v, h);
if (separation > 0.0f)
{
continue;
}
if (node.IsLeaf())
{
RayCastInput subInput;
subInput.p1 = input.p1;
subInput.p2 = input.p2;
subInput.maxFraction = maxFraction;
RayCastOutput output;
callback(out output, ref subInput, node.userData);
if (output.hit)
{
// Early exit.
if (output.fraction == 0.0f)
{
return;
}
maxFraction = output.fraction;
// Update segment bounding box.
{
Vector2 t = p1 + maxFraction * (p2 - p1);
segmentAABB.lowerBound = Vector2.Min(p1, t);
segmentAABB.upperBound = Vector2.Max(p1, t);
}
}
}
else
{
Debug.Assert(count + 1 < k_stackSize);
stack[count++] = node.child1;
stack[count++] = node.child2;
}
}
}
