b2DynamicTree.h

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/*
* Copyright (c) 2009 Erin Catto http://www.box2d.org
*
* This software is provided 'as-is', without any express or implied
* warranty.  In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

#ifndef B2_DYNAMIC_TREE_H
#define B2_DYNAMIC_TREE_H

#include <Box2D/Collision/b2Collision.h>
#include <Box2D/Common/b2GrowableStack.h>

#define b2_nullNode (-1)

struct b2TreeNode
{
        bool IsLeaf() const
        {
                return child1 == b2_nullNode;
        }

        b2AABB aabb;

        void* userData;

        union
        {
                int32 parent;
                int32 next;
        };

        int32 child1;
        int32 child2;

        // leaf = 0, free node = -1
        int32 height;
};

class b2DynamicTree
{
public:
        b2DynamicTree();

        ~b2DynamicTree();

        int32 CreateProxy(const b2AABB& aabb, void* userData);

        void DestroyProxy(int32 proxyId);

        bool MoveProxy(int32 proxyId, const b2AABB& aabb1, const b2Vec2& displacement);

        void* GetUserData(int32 proxyId) const;

        const b2AABB& GetFatAABB(int32 proxyId) const;

        template <typename T>
        void Query(T* callback, const b2AABB& aabb) const;

        template <typename T>
        void RayCast(T* callback, const b2RayCastInput& input) const;

        void Validate() const;

        int32 GetHeight() const;

        int32 GetMaxBalance() const;

        float32 GetAreaRatio() const;

        void RebuildBottomUp();

        void ShiftOrigin(const b2Vec2& newOrigin);

private:

        int32 AllocateNode();
        void FreeNode(int32 node);

        void InsertLeaf(int32 node);
        void RemoveLeaf(int32 node);

        int32 Balance(int32 index);

        int32 ComputeHeight() const;
        int32 ComputeHeight(int32 nodeId) const;

        void ValidateStructure(int32 index) const;
        void ValidateMetrics(int32 index) const;

        int32 m_root;

        b2TreeNode* m_nodes;
        int32 m_nodeCount;
        int32 m_nodeCapacity;

        int32 m_freeList;

        uint32 m_path;

        int32 m_insertionCount;
};

inline void* b2DynamicTree::GetUserData(int32 proxyId) const
{
        b2Assert(0 <= proxyId && proxyId < m_nodeCapacity);
        return m_nodes[proxyId].userData;
}

inline const b2AABB& b2DynamicTree::GetFatAABB(int32 proxyId) const
{
        b2Assert(0 <= proxyId && proxyId < m_nodeCapacity);
        return m_nodes[proxyId].aabb;
}

template <typename T>
inline void b2DynamicTree::Query(T* callback, const b2AABB& aabb) const
{
        b2GrowableStack<int32, 256> stack;
        stack.Push(m_root);

        while (stack.GetCount() > 0)
        {
                int32 nodeId = stack.Pop();
                if (nodeId == b2_nullNode)
                {
                        continue;
                }

                const b2TreeNode* node = m_nodes + nodeId;

                if (b2TestOverlap(node->aabb, aabb))
                {
                        if (node->IsLeaf())
                        {
                                bool proceed = callback->QueryCallback(nodeId);
                                if (proceed == false)
                                {
                                        return;
                                }
                        }
                        else
                        {
                                stack.Push(node->child1);
                                stack.Push(node->child2);
                        }
                }
        }
}

template <typename T>
inline void b2DynamicTree::RayCast(T* callback, const b2RayCastInput& input) const
{
        b2Vec2 p1 = input.p1;
        b2Vec2 p2 = input.p2;
        b2Vec2 r = p2 - p1;
        b2Assert(r.LengthSquared() > 0.0f);
        r.Normalize();

        // v is perpendicular to the segment.
        b2Vec2 v = b2Cross(1.0f, r);
        b2Vec2 abs_v = b2Abs(v);

        // Separating axis for segment (Gino, p80).
        // |dot(v, p1 - c)| > dot(|v|, h)

        float32 maxFraction = input.maxFraction;

        // Build a bounding box for the segment.
        b2AABB segmentAABB;
        {
                b2Vec2 t = p1 + maxFraction * (p2 - p1);
                segmentAABB.lowerBound = b2Min(p1, t);
                segmentAABB.upperBound = b2Max(p1, t);
        }

        b2GrowableStack<int32, 256> stack;
        stack.Push(m_root);

        while (stack.GetCount() > 0)
        {
                int32 nodeId = stack.Pop();
                if (nodeId == b2_nullNode)
                {
                        continue;
                }

                const b2TreeNode* node = m_nodes + nodeId;

                if (b2TestOverlap(node->aabb, segmentAABB) == false)
                {
                        continue;
                }

                // Separating axis for segment (Gino, p80).
                // |dot(v, p1 - c)| > dot(|v|, h)
                b2Vec2 c = node->aabb.GetCenter();
                b2Vec2 h = node->aabb.GetExtents();
                float32 separation = b2Abs(b2Dot(v, p1 - c)) - b2Dot(abs_v, h);
                if (separation > 0.0f)
                {
                        continue;
                }

                if (node->IsLeaf())
                {
                        b2RayCastInput subInput;
                        subInput.p1 = input.p1;
                        subInput.p2 = input.p2;
                        subInput.maxFraction = maxFraction;

                        float32 value = callback->RayCastCallback(subInput, nodeId);

                        if (value == 0.0f)
                        {
                                // The client has terminated the ray cast.
                                return;
                        }

                        if (value > 0.0f)
                        {
                                // Update segment bounding box.
                                maxFraction = value;
                                b2Vec2 t = p1 + maxFraction * (p2 - p1);
                                segmentAABB.lowerBound = b2Min(p1, t);
                                segmentAABB.upperBound = b2Max(p1, t);
                        }
                }
                else
                {
                        stack.Push(node->child1);
                        stack.Push(node->child2);
                }
        }
}

#endif