AStarPathfinder.inl

Go to the documentation of this file.

/*******************************************************************************
Copyright (c) 2005-2009 David Williams

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.
*******************************************************************************/

#include "PolyVoxCore/Impl/ErrorHandling.h"

namespace PolyVox
{
    template<typename VolumeType>
    bool aStarDefaultVoxelValidator(const VolumeType* volData, const Vector3DInt32& v3dPos)
    {
        //Voxels are considered valid candidates for the path if they are inside the volume...
        if(volData->getEnclosingRegion().containsPoint(v3dPos) == false)
        {
            return false;
        }

        return true;
    }

    // AStarPathfinder Class
    template<typename VolumeType>
    AStarPathfinder<VolumeType>::AStarPathfinder(const AStarPathfinderParams<VolumeType>& params)
        :m_params(params)
    {
    }

    template<typename VolumeType>
    void AStarPathfinder<VolumeType>::execute()
    {
        //Clear any existing nodes
        allNodes.clear();
        openNodes.clear();
        closedNodes.clear();

        //Clear the result
        m_params.result->clear();

        //Iterators to start and end node.
        AllNodesContainer::iterator startNode = allNodes.insert(Node(m_params.start.getX(), m_params.start.getY(), m_params.start.getZ())).first;
        AllNodesContainer::iterator endNode = allNodes.insert(Node(m_params.end.getX(), m_params.end.getY(), m_params.end.getZ())).first;

        //Regarding the const_cast - normally you should not modify an object which is in an sdt::set.
        //The reason is that objects in a set are stored sorted in a tree so they can be accessed quickly,
        //and changing the object directly can break the sorting. However, in our case we have provided a
        //custom sort operator for the set which we know only uses the position to sort. Hence we can safely
        //modify other properties of the object while it is in the set.
        Node* tempStart = const_cast<Node*>(&(*startNode));
        tempStart->gVal = 0;
        tempStart->hVal = computeH(startNode->position, endNode->position);

        Node* tempEnd = const_cast<Node*>(&(*endNode));
        tempEnd->hVal = 0.0f;

        openNodes.insert(startNode);

        float fDistStartToEnd = (endNode->position - startNode->position).length();
        m_fProgress = 0.0f;
        if(m_params.progressCallback)
        {
            m_params.progressCallback(m_fProgress);
        }

        while((openNodes.empty() == false) && (openNodes.getFirst() != endNode))
        {
            //Move the first node from open to closed.
            current = openNodes.getFirst();
            openNodes.removeFirst();
            closedNodes.insert(current);

            //Update the user on our progress
            if(m_params.progressCallback)
            {
                const float fMinProgresIncreament = 0.001f;
                float fDistCurrentToEnd = (endNode->position - current->position).length();
                float fDistNormalised = fDistCurrentToEnd / fDistStartToEnd;
                float fProgress = 1.0f - fDistNormalised;
                if(fProgress >= m_fProgress + fMinProgresIncreament)
                {
                    m_fProgress = fProgress;
                    m_params.progressCallback(m_fProgress);
                }
            }

            //The distance from one cell to another connected by face, edge, or corner.
            const float fFaceCost = sqrt_1;
            const float fEdgeCost = sqrt_2;
            const float fCornerCost = sqrt_3;

            //Process the neighbours. Note the deliberate lack of 'break' 
            //statements, larger connectivities include smaller ones.
            switch(m_params.connectivity)
            {
            case TwentySixConnected:
                processNeighbour(current->position + arrayPathfinderCorners[0], current->gVal + fCornerCost);
                processNeighbour(current->position + arrayPathfinderCorners[1], current->gVal + fCornerCost);
                processNeighbour(current->position + arrayPathfinderCorners[2], current->gVal + fCornerCost);
                processNeighbour(current->position + arrayPathfinderCorners[3], current->gVal + fCornerCost);
                processNeighbour(current->position + arrayPathfinderCorners[4], current->gVal + fCornerCost);
                processNeighbour(current->position + arrayPathfinderCorners[5], current->gVal + fCornerCost);
                processNeighbour(current->position + arrayPathfinderCorners[6], current->gVal + fCornerCost);
                processNeighbour(current->position + arrayPathfinderCorners[7], current->gVal + fCornerCost);

            case EighteenConnected:
                processNeighbour(current->position + arrayPathfinderEdges[ 0], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[ 1], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[ 2], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[ 3], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[ 4], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[ 5], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[ 6], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[ 7], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[ 8], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[ 9], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[10], current->gVal + fEdgeCost);
                processNeighbour(current->position + arrayPathfinderEdges[11], current->gVal + fEdgeCost);

            case SixConnected:
                processNeighbour(current->position + arrayPathfinderFaces[0], current->gVal + fFaceCost);
                processNeighbour(current->position + arrayPathfinderFaces[1], current->gVal + fFaceCost);
                processNeighbour(current->position + arrayPathfinderFaces[2], current->gVal + fFaceCost);
                processNeighbour(current->position + arrayPathfinderFaces[3], current->gVal + fFaceCost);
                processNeighbour(current->position + arrayPathfinderFaces[4], current->gVal + fFaceCost);
                processNeighbour(current->position + arrayPathfinderFaces[5], current->gVal + fFaceCost);
            }

            if(allNodes.size() > m_params.maxNumberOfNodes)
            {
                //We've reached the specified maximum number
                //of nodes. Just give up on the search.
                break;
            }
        }

        if((openNodes.empty()) || (openNodes.getFirst() != endNode))
        {
            //In this case we failed to find a valid path.
            POLYVOX_THROW(std::runtime_error, "No path found");
        }
        else
        {
            //Regarding the const_cast - normally you should not modify an object which is in an sdt::set.
            //The reason is that objects in a set are stored sorted in a tree so they can be accessed quickly,
            //and changing the object directly can break the sorting. However, in our case we have provided a
            //custom sort operator for the set which we know only uses the position to sort. Hence we can safely
            //modify other properties of the object while it is in the set.
            Node* n = const_cast<Node*>(&(*endNode));
            while(n != 0)
            {
                m_params.result->push_front(n->position);
                n = n->parent;
            }
        }

        if(m_params.progressCallback)
        {
            m_params.progressCallback(1.0f);
        }
    }

    template<typename VolumeType>
    void AStarPathfinder<VolumeType>::processNeighbour(const Vector3DInt32& neighbourPos, float neighbourGVal)
    {
        bool bIsVoxelValidForPath = m_params.isVoxelValidForPath(m_params.volume, neighbourPos);
        if(!bIsVoxelValidForPath)
        {
            return;
        }

        float cost = neighbourGVal;

        std::pair<AllNodesContainer::iterator, bool> insertResult = allNodes.insert(Node(neighbourPos.getX(), neighbourPos.getY(), neighbourPos.getZ()));
        AllNodesContainer::iterator neighbour = insertResult.first;

        if(insertResult.second == true) //New node, compute h.
        {
            Node* tempNeighbour = const_cast<Node*>(&(*neighbour));
            tempNeighbour -> hVal = computeH(neighbour->position, m_params.end);
        }

        OpenNodesContainer::iterator openIter = openNodes.find(neighbour);
        if(openIter != openNodes.end())
        {
            if(cost < neighbour->gVal)
            {
                openNodes.remove(openIter);
                openIter = openNodes.end();
            }
        }

        //TODO - Nodes could keep track of if they are in open or closed? And a pointer to where they are?
        ClosedNodesContainer::iterator closedIter = closedNodes.find(neighbour);
        if(closedIter != closedNodes.end())
        {
            if(cost < neighbour->gVal)
            {
                //Probably shouldn't happen?
                closedNodes.remove(closedIter);
                closedIter = closedNodes.end();
            }
        }

        if((openIter == openNodes.end()) && (closedIter == closedNodes.end()))
        {
            //Regarding the const_cast - normally you should not modify an object which is in an sdt::set.
            //The reason is that objects in a set are stored sorted in a tree so they can be accessed quickly,
            //and changing the object directly can break the sorting. However, in our case we have provided a
            //custom sort operator for the set which we know only uses the position to sort. Hence we can safely
            //modify other properties of the object while it is in the set.
            Node* temp = const_cast<Node*>(&(*neighbour));
            temp->gVal = cost;
            openNodes.insert(neighbour);
            temp->parent = const_cast<Node*>(&(*current));
        }
    }

    template<typename VolumeType>
    float AStarPathfinder<VolumeType>::SixConnectedCost(const Vector3DInt32& a, const Vector3DInt32& b)
    {
        //This is the only heuristic I'm sure of - just use the manhatten distance for the 6-connected case.
        uint32_t faceSteps = std::abs(a.getX()-b.getX()) + std::abs(a.getY()-b.getY()) + std::abs(a.getZ()-b.getZ());

        return faceSteps * 1.0f;
    }

    template<typename VolumeType>
    float AStarPathfinder<VolumeType>::EighteenConnectedCost(const Vector3DInt32& a, const Vector3DInt32& b)
    {
        //I'm not sure of the correct heuristic for the 18-connected case, so I'm just letting it fall through to the 
        //6-connected case. This means 'h' will be bigger than it should be, resulting in a faster path which may not 
        //actually be the shortest one. If you have a correct heuristic for the 18-connected case then please let me know.

        return SixConnectedCost(a,b);
    }

    template<typename VolumeType>
    float AStarPathfinder<VolumeType>::TwentySixConnectedCost(const Vector3DInt32& a, const Vector3DInt32& b)
    {
        //Can't say I'm certain about this heuristic - if anyone has
        //a better idea of what it should be then please let me know.
        uint32_t array[3];
        array[0] = std::abs(a.getX() - b.getX());
        array[1] = std::abs(a.getY() - b.getY());
        array[2] = std::abs(a.getZ() - b.getZ());
        
        //Maybe this is better implemented directly
        //using three compares and two swaps... but not
        //until the profiler says so.
        std::sort(&array[0], &array[3]);

        uint32_t cornerSteps = array[0];
        uint32_t edgeSteps = array[1] - array[0];
        uint32_t faceSteps = array[2] - array[1];

        return cornerSteps * sqrt_3 + edgeSteps * sqrt_2 + faceSteps * sqrt_1;
    }

    template<typename VolumeType>
    float AStarPathfinder<VolumeType>::computeH(const Vector3DInt32& a, const Vector3DInt32& b)
    {
        float hVal;
            
        switch(m_params.connectivity)
        {
        case TwentySixConnected:
            hVal = TwentySixConnectedCost(a, b);
            break;
        case EighteenConnected:
            hVal = EighteenConnectedCost(a, b);
            break;
        case SixConnected:              
            hVal = SixConnectedCost(a, b);
            break;
        default:
            POLYVOX_ASSERT(false, "Invalid case");
        }

        //Sanity checks in debug mode. These can come out eventually, but I
        //want to make sure that the heuristics I've come up with make sense.
        POLYVOX_ASSERT((a-b).length() <= TwentySixConnectedCost(a,b), "A* heuristic error.");
        POLYVOX_ASSERT(TwentySixConnectedCost(a,b) <= EighteenConnectedCost(a,b), "A* heuristic error.");
        POLYVOX_ASSERT(EighteenConnectedCost(a,b) <= SixConnectedCost(a,b), "A* heuristic error.");

        //Apply the bias to the computed h value;
        hVal *= m_params.hBias;

        //Having computed hVal, we now apply some random bias to break ties.
        //This needs to be deterministic on the input position. This random
        //bias means it is much les likely that two paths are exactly the same
        //length, and so far fewer nodes must be expanded to find the shortest path.
        //See http://theory.stanford.edu/~amitp/GameProgramming/Heuristics.html#S12

        //Note that if the hash is zero we can have differences between the Linux vs. Windows
        //(or perhaps GCC vs. VS) versions of the code. This is probably because of the way
        //sorting inside the std::set works (i.e. one system swaps values which are identical
        //while the other one doesn't - both approaches are valid). For the same reason we want
        //to make sure that position (x,y,z) has a differnt hash from e.g. position (x,z,y).
        uint32_t aX = (a.getX() << 16) & 0x00FF0000;
        uint32_t aY = (a.getY() <<  8) & 0x0000FF00;
        uint32_t aZ = (a.getZ()      ) & 0x000000FF;
        uint32_t hashVal = hash(aX | aY | aZ);

        //Stop hashVal going over 65535, and divide by 1000000 to make sure it is small.
        hashVal &= 0x0000FFFF;
        float fHash = hashVal / 1000000.0f;

        //Apply the hash and return
        hVal += fHash;
        return hVal;
    }

    // Robert Jenkins' 32 bit integer hash function
    // http://www.burtleburtle.net/bob/hash/integer.html
    template<typename VolumeType>
    uint32_t AStarPathfinder<VolumeType>::hash( uint32_t a)
    {
        a = (a+0x7ed55d16) + (a<<12);
        a = (a^0xc761c23c) ^ (a>>19);
        a = (a+0x165667b1) + (a<<5);
        a = (a+0xd3a2646c) ^ (a<<9);
        a = (a+0xfd7046c5) + (a<<3);
        a = (a^0xb55a4f09) ^ (a>>16);
        return a;
    }
}