b2_dynamic_tree.h

// MIT License
 
// Copyright (c) 2019 Erin Catto
 
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
 
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
 
#ifndef B2_DYNAMIC_TREE_H
#define B2_DYNAMIC_TREE_H
 
#include "b2_api.h"
#include "b2_collision.h"
#include "b2_growable_stack.h"
 
#define b2_nullNode (-1)
 
struct B2_API 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;
 
    bool moved;
};
 
class B2_API 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;
 
    bool WasMoved(int32 proxyId) const;
    void ClearMoved(int32 proxyId);
 
    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;
 
    float 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;
 
    int32 m_insertionCount;
};
 
inline void* b2DynamicTree::GetUserData(int32 proxyId) const
{
    b2Assert(0 <= proxyId && proxyId < m_nodeCapacity);
    return m_nodes[proxyId].userData;
}
 
inline bool b2DynamicTree::WasMoved(int32 proxyId) const
{
    b2Assert(0 <= proxyId && proxyId < m_nodeCapacity);
    return m_nodes[proxyId].moved;
}
 
inline void b2DynamicTree::ClearMoved(int32 proxyId)
{
    b2Assert(0 <= proxyId && proxyId < m_nodeCapacity);
    m_nodes[proxyId].moved = false;
}
 
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)
 
    float 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();
        float 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;
 
            float 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