LargeVolume.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"

//Included here rather than in the .h because it refers to LargeVolume (avoids forward declaration)
#include "PolyVoxCore/ConstVolumeProxy.h"

namespace PolyVox
{
    template <typename VoxelType>
    LargeVolume<VoxelType>::LargeVolume
    (
        polyvox_function<void(const ConstVolumeProxy<VoxelType>&, const Region&)> dataRequiredHandler,
        polyvox_function<void(const ConstVolumeProxy<VoxelType>&, const Region&)> dataOverflowHandler,
        uint16_t uBlockSideLength
    )
    :BaseVolume<VoxelType>(Region::MaxRegion)
    {
        m_funcDataRequiredHandler = dataRequiredHandler;
        m_funcDataOverflowHandler = dataOverflowHandler;
        m_bPagingEnabled = true;
        //Create a volume of the right size.
        initialise(Region::MaxRegion,uBlockSideLength);
    }

    template <typename VoxelType>
    LargeVolume<VoxelType>::LargeVolume
    (
        const Region& regValid,
        Compressor* pCompressor,
        polyvox_function<void(const ConstVolumeProxy<VoxelType>&, const Region&)> dataRequiredHandler,
        polyvox_function<void(const ConstVolumeProxy<VoxelType>&, const Region&)> dataOverflowHandler,
        bool bPagingEnabled,
        uint16_t uBlockSideLength
    )
    :BaseVolume<VoxelType>(regValid)
    ,m_pCompressor(pCompressor)
    {
        m_funcDataRequiredHandler = dataRequiredHandler;
        m_funcDataOverflowHandler = dataOverflowHandler;
        m_bPagingEnabled = bPagingEnabled;

        //Create a volume of the right size.
        initialise(regValid,uBlockSideLength);
    }

    template <typename VoxelType>
    LargeVolume<VoxelType>::LargeVolume(const LargeVolume<VoxelType>& /*rhs*/)
    {
        POLYVOX_ASSERT(false, "Copy constructor not implemented."); // See function comment above.
    }

    template <typename VoxelType>
    LargeVolume<VoxelType>::~LargeVolume()
    {
        flushAll();
    }

    template <typename VoxelType>
    LargeVolume<VoxelType>& LargeVolume<VoxelType>::operator=(const LargeVolume<VoxelType>& /*rhs*/)
    {
        POLYVOX_ASSERT(false, "Assignment operator not implemented."); // See function comment above.
    }

    template <typename VoxelType>
    VoxelType LargeVolume<VoxelType>::getVoxel(int32_t uXPos, int32_t uYPos, int32_t uZPos) const
    {
        POLYVOX_ASSERT(this->m_regValidRegion.containsPoint(Vector3DInt32(uXPos, uYPos, uZPos)), "Position is outside valid region");

        const int32_t blockX = uXPos >> m_uBlockSideLengthPower;
        const int32_t blockY = uYPos >> m_uBlockSideLengthPower;
        const int32_t blockZ = uZPos >> m_uBlockSideLengthPower;

        const uint16_t xOffset = static_cast<uint16_t>(uXPos - (blockX << m_uBlockSideLengthPower));
        const uint16_t yOffset = static_cast<uint16_t>(uYPos - (blockY << m_uBlockSideLengthPower));
        const uint16_t zOffset = static_cast<uint16_t>(uZPos - (blockZ << m_uBlockSideLengthPower));

        Block<VoxelType>* pUncompressedBlock = getUncompressedBlock(blockX, blockY, blockZ);

        return pUncompressedBlock->getVoxelAt(xOffset,yOffset,zOffset);
    }

    template <typename VoxelType>
    VoxelType LargeVolume<VoxelType>::getVoxel(const Vector3DInt32& v3dPos) const
    {
        return getVoxel(v3dPos.getX(), v3dPos.getY(), v3dPos.getZ());
    }

    template <typename VoxelType>
    VoxelType LargeVolume<VoxelType>::getVoxelAt(int32_t uXPos, int32_t uYPos, int32_t uZPos) const
    {
        if(this->m_regValidRegion.containsPoint(Vector3DInt32(uXPos, uYPos, uZPos)))
        {
            const int32_t blockX = uXPos >> m_uBlockSideLengthPower;
            const int32_t blockY = uYPos >> m_uBlockSideLengthPower;
            const int32_t blockZ = uZPos >> m_uBlockSideLengthPower;

            const uint16_t xOffset = static_cast<uint16_t>(uXPos - (blockX << m_uBlockSideLengthPower));
            const uint16_t yOffset = static_cast<uint16_t>(uYPos - (blockY << m_uBlockSideLengthPower));
            const uint16_t zOffset = static_cast<uint16_t>(uZPos - (blockZ << m_uBlockSideLengthPower));

            Block<VoxelType>* pUncompressedBlock = getUncompressedBlock(blockX, blockY, blockZ);

            return pUncompressedBlock->getVoxelAt(xOffset,yOffset,zOffset);
        }
        else
        {
            return this->getBorderValue();
        }
    }

    template <typename VoxelType>
    VoxelType LargeVolume<VoxelType>::getVoxelAt(const Vector3DInt32& v3dPos) const
    {
        return getVoxelAt(v3dPos.getX(), v3dPos.getY(), v3dPos.getZ());
    }

    template <typename VoxelType>
    VoxelType LargeVolume<VoxelType>::getVoxelWithWrapping(int32_t uXPos, int32_t uYPos, int32_t uZPos, WrapMode eWrapMode, VoxelType tBorder) const
    {
        switch(eWrapMode)
        {
            case WrapModes::Clamp:
            {
                //Perform clamping
                uXPos = (std::max)(uXPos, this->m_regValidRegion.getLowerX());
                uYPos = (std::max)(uYPos, this->m_regValidRegion.getLowerY());
                uZPos = (std::max)(uZPos, this->m_regValidRegion.getLowerZ());
                uXPos = (std::min)(uXPos, this->m_regValidRegion.getUpperX());
                uYPos = (std::min)(uYPos, this->m_regValidRegion.getUpperY());
                uZPos = (std::min)(uZPos, this->m_regValidRegion.getUpperZ());

                //Get the voxel value
                return getVoxel(uXPos, uYPos, uZPos);
                //No need to break as we've returned
            }
            case WrapModes::Border:
            {
                if(this->m_regValidRegion.containsPoint(uXPos, uYPos, uZPos))
                {
                    return getVoxel(uXPos, uYPos, uZPos);
                }
                else
                {
                    return tBorder;
                }
                //No need to break as we've returned
            }
            default:
            {
                //Should never happen
                POLYVOX_ASSERT(false, "Invlaid case.");
                return VoxelType();
            }
        }
    }

    template <typename VoxelType>
    VoxelType LargeVolume<VoxelType>::getVoxelWithWrapping(const Vector3DInt32& v3dPos, WrapMode eWrapMode, VoxelType tBorder) const
    {
        return getVoxelWithWrapping(v3dPos.getX(), v3dPos.getY(), v3dPos.getZ(), eWrapMode, tBorder);
    }

    template <typename VoxelType>
    void LargeVolume<VoxelType>::setMaxNumberOfUncompressedBlocks(uint32_t uMaxNumberOfUncompressedBlocks)
    {
        clearBlockCache();

        m_uMaxNumberOfUncompressedBlocks = uMaxNumberOfUncompressedBlocks;
    }

    template <typename VoxelType>
    void LargeVolume<VoxelType>::setMaxNumberOfBlocksInMemory(uint32_t uMaxNumberOfBlocksInMemory)
    {
        if(m_pBlocks.size() > uMaxNumberOfBlocksInMemory)
        {
            flushAll();
        }
        m_uMaxNumberOfBlocksInMemory  = uMaxNumberOfBlocksInMemory;
    }

    template <typename VoxelType>
    bool LargeVolume<VoxelType>::setVoxelAt(int32_t uXPos, int32_t uYPos, int32_t uZPos, VoxelType tValue)
    {
        POLYVOX_ASSERT(this->m_regValidRegion.containsPoint(Vector3DInt32(uXPos, uYPos, uZPos)), "Position is outside valid region");

        const int32_t blockX = uXPos >> m_uBlockSideLengthPower;
        const int32_t blockY = uYPos >> m_uBlockSideLengthPower;
        const int32_t blockZ = uZPos >> m_uBlockSideLengthPower;

        const uint16_t xOffset = static_cast<uint16_t>(uXPos - (blockX << m_uBlockSideLengthPower));
        const uint16_t yOffset = static_cast<uint16_t>(uYPos - (blockY << m_uBlockSideLengthPower));
        const uint16_t zOffset = static_cast<uint16_t>(uZPos - (blockZ << m_uBlockSideLengthPower));

        Block<VoxelType>* pUncompressedBlock = getUncompressedBlock(blockX, blockY, blockZ);

        pUncompressedBlock->setVoxelAt(xOffset,yOffset,zOffset, tValue);

        //Return true to indicate that we modified a voxel.
        return true;
    }

    template <typename VoxelType>
    bool LargeVolume<VoxelType>::setVoxelAt(const Vector3DInt32& v3dPos, VoxelType tValue)
    {
        return setVoxelAt(v3dPos.getX(), v3dPos.getY(), v3dPos.getZ(), tValue);
    }


    template <typename VoxelType>
    void LargeVolume<VoxelType>::prefetch(Region regPrefetch)
    {
        Vector3DInt32 v3dStart;
        for(int i = 0; i < 3; i++)
        {
            v3dStart.setElement(i, regPrefetch.getLowerCorner().getElement(i) >> m_uBlockSideLengthPower);
        }

        Vector3DInt32 v3dEnd;
        for(int i = 0; i < 3; i++)
        {
            v3dEnd.setElement(i, regPrefetch.getUpperCorner().getElement(i) >> m_uBlockSideLengthPower);
        }

        Vector3DInt32 v3dSize = v3dEnd - v3dStart + Vector3DInt32(1,1,1);
        uint32_t numblocks = static_cast<uint32_t>(v3dSize.getX() * v3dSize.getY() * v3dSize.getZ());
        if(numblocks > m_uMaxNumberOfBlocksInMemory)
        {
            // cannot support the amount of blocks... so only load the maximum possible
            numblocks = m_uMaxNumberOfBlocksInMemory;
        }
        for(int32_t x = v3dStart.getX(); x <= v3dEnd.getX(); x++)
        {
            for(int32_t y = v3dStart.getY(); y <= v3dEnd.getY(); y++)
            {
                for(int32_t z = v3dStart.getZ(); z <= v3dEnd.getZ(); z++)
                {
                    Vector3DInt32 pos(x,y,z);
                    typename std::map<Vector3DInt32, LoadedBlock, BlockPositionCompare>::iterator itBlock = m_pBlocks.find(pos);
                    
                    if(itBlock != m_pBlocks.end())
                    {
                        // If the block is already loaded then we don't load it again. This means it does not get uncompressed,
                        // whereas if we were to call getUncompressedBlock() regardless then it would also get uncompressed.
                        // This might be nice, but on the prefetch region could be bigger than the uncompressed cache size.
                        // This would limit the amount of prefetching we could do.
                        continue;
                    }

                    if(numblocks == 0)
                    {
                        // Loading any more blocks would attempt to overflow the memory and therefore erase blocks
                        // we loaded in the beginning. This wouldn't cause logic problems but would be wasteful.
                        return;
                    }
                    // load a block
                    numblocks--;
                    getUncompressedBlock(x,y,z);
                } // for z
            } // for y
        } // for x
    }

    template <typename VoxelType>
    void LargeVolume<VoxelType>::flushAll()
    {
        typename std::map<Vector3DInt32, LoadedBlock, BlockPositionCompare>::iterator i;
        //Replaced the for loop here as the call to
        //eraseBlock was invalidating the iterator.
        while(m_pBlocks.size() > 0)
        {
            eraseBlock(m_pBlocks.begin());
        }
    }

    template <typename VoxelType>
    void LargeVolume<VoxelType>::flush(Region regFlush)
    {
        Vector3DInt32 v3dStart;
        for(int i = 0; i < 3; i++)
        {
            v3dStart.setElement(i, regFlush.getLowerCorner().getElement(i) >> m_uBlockSideLengthPower);
        }

        Vector3DInt32 v3dEnd;
        for(int i = 0; i < 3; i++)
        {
            v3dEnd.setElement(i, regFlush.getUpperCorner().getElement(i) >> m_uBlockSideLengthPower);
        }

        for(int32_t x = v3dStart.getX(); x <= v3dEnd.getX(); x++)
        {
            for(int32_t y = v3dStart.getY(); y <= v3dEnd.getY(); y++)
            {
                for(int32_t z = v3dStart.getZ(); z <= v3dEnd.getZ(); z++)
                {
                    Vector3DInt32 pos(x,y,z);
                    typename std::map<Vector3DInt32, LoadedBlock, BlockPositionCompare>::iterator itBlock = m_pBlocks.find(pos);
                    if(itBlock == m_pBlocks.end())
                    {
                        // not loaded, not unloading
                        continue;
                    }
                    eraseBlock(itBlock);
                    // eraseBlock might cause a call to getUncompressedBlock, which again sets m_pLastAccessedBlock
                    if(m_v3dLastAccessedBlockPos == pos)
                    {
                        m_pLastAccessedBlock = 0;
                    }
                } // for z
            } // for y
        } // for x
    }

    template <typename VoxelType>
    void LargeVolume<VoxelType>::clearBlockCache(void)
    {
        for(uint32_t ct = 0; ct < m_vecUncompressedBlockCache.size(); ct++)
        {
            m_vecUncompressedBlockCache[ct]->block.compress(m_pCompressor);
        }
        m_vecUncompressedBlockCache.clear();
    }

    template <typename VoxelType>
    void LargeVolume<VoxelType>::initialise(const Region& regValidRegion, uint16_t uBlockSideLength)
    {
        //Debug mode validation
        POLYVOX_ASSERT(uBlockSideLength > 0, "Block side length cannot be zero.");
        POLYVOX_ASSERT(isPowerOf2(uBlockSideLength), "Block side length must be a power of two.");
        POLYVOX_ASSERT(m_pCompressor, "You must provide a compressor for the LargeVolume to use.");
        
        //Release mode validation
        if(uBlockSideLength == 0)
        {
            POLYVOX_THROW(std::invalid_argument, "Block side length cannot be zero.");
        }
        if(!isPowerOf2(uBlockSideLength))
        {
            POLYVOX_THROW(std::invalid_argument, "Block side length must be a power of two.");
        }
        if(!m_pCompressor)
        {
            POLYVOX_THROW(std::invalid_argument, "You must provide a compressor for the LargeVolume to use.");
        }

        m_uTimestamper = 0;
        m_uMaxNumberOfUncompressedBlocks = 16;
        m_uBlockSideLength = uBlockSideLength;
        m_uMaxNumberOfBlocksInMemory = 1024;
        m_v3dLastAccessedBlockPos = Vector3DInt32(0,0,0); //There are no invalid positions, but initially the m_pLastAccessedBlock pointer will be null;
        m_pLastAccessedBlock = 0;

        this->m_regValidRegion = regValidRegion;

        //Compute the block side length
        m_uBlockSideLength = uBlockSideLength;
        m_uBlockSideLengthPower = logBase2(m_uBlockSideLength);

        m_regValidRegionInBlocks.setLowerX(this->m_regValidRegion.getLowerX() >> m_uBlockSideLengthPower);
        m_regValidRegionInBlocks.setLowerY(this->m_regValidRegion.getLowerY() >> m_uBlockSideLengthPower);
        m_regValidRegionInBlocks.setLowerZ(this->m_regValidRegion.getLowerZ() >> m_uBlockSideLengthPower);
        m_regValidRegionInBlocks.setUpperX(this->m_regValidRegion.getUpperX() >> m_uBlockSideLengthPower);
        m_regValidRegionInBlocks.setUpperY(this->m_regValidRegion.getUpperY() >> m_uBlockSideLengthPower);
        m_regValidRegionInBlocks.setUpperZ(this->m_regValidRegion.getUpperZ() >> m_uBlockSideLengthPower);

        setMaxNumberOfUncompressedBlocks(m_uMaxNumberOfUncompressedBlocks);

        //Clear the previous data
        m_pBlocks.clear();

        //Clear the previous data
        m_pBlocks.clear();

        //Other properties we might find useful later
        this->m_uLongestSideLength = (std::max)((std::max)(this->getWidth(),this->getHeight()),this->getDepth());
        this->m_uShortestSideLength = (std::min)((std::min)(this->getWidth(),this->getHeight()),this->getDepth());
        this->m_fDiagonalLength = sqrtf(static_cast<float>(this->getWidth() * this->getWidth() + this->getHeight() * this->getHeight() + this->getDepth() * this->getDepth()));
    }

    template <typename VoxelType>
    void LargeVolume<VoxelType>::eraseBlock(typename std::map<Vector3DInt32, LoadedBlock, BlockPositionCompare>::iterator itBlock) const
    {
        if(m_funcDataOverflowHandler)
        {
            Vector3DInt32 v3dPos = itBlock->first;
            Vector3DInt32 v3dLower(v3dPos.getX() << m_uBlockSideLengthPower, v3dPos.getY() << m_uBlockSideLengthPower, v3dPos.getZ() << m_uBlockSideLengthPower);
            Vector3DInt32 v3dUpper = v3dLower + Vector3DInt32(m_uBlockSideLength-1, m_uBlockSideLength-1, m_uBlockSideLength-1);

            Region reg(v3dLower, v3dUpper);
            ConstVolumeProxy<VoxelType> ConstVolumeProxy(*this, reg);

            m_funcDataOverflowHandler(ConstVolumeProxy, reg);
        }
        if(m_pCompressor)
        {
            for(uint32_t ct = 0; ct < m_vecUncompressedBlockCache.size(); ct++)
            {
                // find the block in the uncompressed cache
                if(m_vecUncompressedBlockCache[ct] == &(itBlock->second))
                {
                    // TODO: compression is unneccessary? or will not compressing this cause a memleak?
                    itBlock->second.block.compress(m_pCompressor);
                    // put last object in cache here
                    m_vecUncompressedBlockCache[ct] = m_vecUncompressedBlockCache.back();
                    // decrease cache size by one since last element is now in here twice
                    m_vecUncompressedBlockCache.resize(m_vecUncompressedBlockCache.size()-1);
                    break;
                }
            }
        }
        m_pBlocks.erase(itBlock);
    }

    template <typename VoxelType>
    bool LargeVolume<VoxelType>::setVoxelAtConst(int32_t uXPos, int32_t uYPos, int32_t uZPos, VoxelType tValue) const
    {
        //We don't have any range checks in this function because it
        //is a private function only called by the ConstVolumeProxy. The
        //ConstVolumeProxy takes care of ensuring the range is appropriate.

        const int32_t blockX = uXPos >> m_uBlockSideLengthPower;
        const int32_t blockY = uYPos >> m_uBlockSideLengthPower;
        const int32_t blockZ = uZPos >> m_uBlockSideLengthPower;

        const uint16_t xOffset = uXPos - (blockX << m_uBlockSideLengthPower);
        const uint16_t yOffset = uYPos - (blockY << m_uBlockSideLengthPower);
        const uint16_t zOffset = uZPos - (blockZ << m_uBlockSideLengthPower);

        Block<VoxelType>* pUncompressedBlock = getUncompressedBlock(blockX, blockY, blockZ);

        pUncompressedBlock->setVoxelAt(xOffset,yOffset,zOffset, tValue);

        //Return true to indicate that we modified a voxel.
        return true;
    }


    template <typename VoxelType>
    Block<VoxelType>* LargeVolume<VoxelType>::getUncompressedBlock(int32_t uBlockX, int32_t uBlockY, int32_t uBlockZ) const
    {
        Vector3DInt32 v3dBlockPos(uBlockX, uBlockY, uBlockZ);

        //Check if we have the same block as last time, if so there's no need to even update
        //the time stamp. If we updated it everytime then that would be every time we touched
        //a voxel, which would overflow a uint32_t and require us to use a uint64_t instead.
        //This check should also provide a significant speed boost as usually it is true.
        if((v3dBlockPos == m_v3dLastAccessedBlockPos) && (m_pLastAccessedBlock != 0))
        {
            POLYVOX_ASSERT(m_pLastAccessedBlock->m_tUncompressedData, "Block has no uncompressed data");
            return m_pLastAccessedBlock;
        }       

        typename std::map<Vector3DInt32, LoadedBlock, BlockPositionCompare>::iterator itBlock = m_pBlocks.find(v3dBlockPos);
        // check whether the block is already loaded
        if(itBlock == m_pBlocks.end())
        {
            //The block is not in the map, so we will have to create a new block and add it.
            //Before we do so, we might want to dump some existing data to make space. We 
            //Only do this if paging is enabled.
            if(m_bPagingEnabled)
            {
                // check wether another block needs to be unloaded before this one can be loaded
                if(m_pBlocks.size() == m_uMaxNumberOfBlocksInMemory)
                {
                    // find the least recently used block
                    typename std::map<Vector3DInt32, LoadedBlock, BlockPositionCompare>::iterator i;
                    typename std::map<Vector3DInt32, LoadedBlock, BlockPositionCompare>::iterator itUnloadBlock = m_pBlocks.begin();
                    for(i = m_pBlocks.begin(); i != m_pBlocks.end(); i++)
                    {
                        if(i->second.timestamp < itUnloadBlock->second.timestamp)
                        {
                            itUnloadBlock = i;
                        }
                    }
                    eraseBlock(itUnloadBlock);
                }
            }
            
            // create the new block
            LoadedBlock newBlock(m_uBlockSideLength);

            // Blocks start out compressed - should we change this?
            // Or maybe we should just 'seed' them with compressed data,
            // rather than creating an empty block and then compressing?
            newBlock.block.compress(m_pCompressor);

            itBlock = m_pBlocks.insert(std::make_pair(v3dBlockPos, newBlock)).first;

            //We have created the new block. If paging is enabled it should be used to
            //fill in the required data. Otherwise it is just left in the default state.
            if(m_bPagingEnabled)
            {
                if(m_funcDataRequiredHandler)
                {
                    // "load" will actually call setVoxel, which will in turn call this function again but the block will be found
                    // so this if(itBlock == m_pBlocks.end()) never is entered      
                    //FIXME - can we pass the block around so that we don't have to find  it again when we recursively call this function?
                    Vector3DInt32 v3dLower(v3dBlockPos.getX() << m_uBlockSideLengthPower, v3dBlockPos.getY() << m_uBlockSideLengthPower, v3dBlockPos.getZ() << m_uBlockSideLengthPower);
                    Vector3DInt32 v3dUpper = v3dLower + Vector3DInt32(m_uBlockSideLength-1, m_uBlockSideLength-1, m_uBlockSideLength-1);
                    Region reg(v3dLower, v3dUpper);
                    ConstVolumeProxy<VoxelType> ConstVolumeProxy(*this, reg);
                    m_funcDataRequiredHandler(ConstVolumeProxy, reg);
                }
            }
        }       

        //Get the block and mark that we accessed it
        LoadedBlock& loadedBlock = itBlock->second;
        loadedBlock.timestamp = ++m_uTimestamper;
        m_v3dLastAccessedBlockPos = v3dBlockPos;
        m_pLastAccessedBlock = &(loadedBlock.block);

        if(loadedBlock.block.m_bIsCompressed == false)
        {           
            POLYVOX_ASSERT(m_pLastAccessedBlock->m_tUncompressedData, "Block has no uncompressed data");
            return m_pLastAccessedBlock;
        }

        //If we are allowed to compress then check whether we need to
        if((m_pCompressor) && (m_vecUncompressedBlockCache.size() == m_uMaxNumberOfUncompressedBlocks))
        {
            int32_t leastRecentlyUsedBlockIndex = -1;
            uint32_t uLeastRecentTimestamp = (std::numeric_limits<uint32_t>::max)();

            //Currently we find the oldest block by iterating over the whole array. Of course we could store the blocks sorted by
            //timestamp (set, priority_queue, etc) but then we'll need to move them around as the timestamp changes. Can come back 
            //to this if it proves to be a bottleneck (compraed to the cost of actually doing the compression/decompression).
            for(uint32_t ct = 0; ct < m_vecUncompressedBlockCache.size(); ct++)
            {
                if(m_vecUncompressedBlockCache[ct]->timestamp < uLeastRecentTimestamp)
                {
                    uLeastRecentTimestamp = m_vecUncompressedBlockCache[ct]->timestamp;
                    leastRecentlyUsedBlockIndex = ct;
                }
            }
            
            //Compress the least recently used block.
            m_vecUncompressedBlockCache[leastRecentlyUsedBlockIndex]->block.compress(m_pCompressor);

            //We don't actually remove any elements from this vector, we
            //simply change the pointer to point at the new uncompressed bloack.            
            m_vecUncompressedBlockCache[leastRecentlyUsedBlockIndex] = &loadedBlock;
        }
        else
        {
            m_vecUncompressedBlockCache.push_back(&loadedBlock);
        }
        
        loadedBlock.block.uncompress(m_pCompressor);

        m_pLastAccessedBlock = &(loadedBlock.block);
        POLYVOX_ASSERT(m_pLastAccessedBlock->m_tUncompressedData, "Block has no uncompressed data");
        return m_pLastAccessedBlock;
    }

    template <typename VoxelType>
    float LargeVolume<VoxelType>::calculateCompressionRatio(void)
    {
        float fRawSize = static_cast<float>(m_pBlocks.size() * m_uBlockSideLength * m_uBlockSideLength* m_uBlockSideLength * sizeof(VoxelType));
        float fCompressedSize = static_cast<float>(calculateSizeInBytes());
        return fCompressedSize/fRawSize;
    }

    template <typename VoxelType>
    uint32_t LargeVolume<VoxelType>::calculateSizeInBytes(void)
    {
        uint32_t uSizeInBytes = sizeof(LargeVolume);

        //Memory used by the blocks
        typename std::map<Vector3DInt32, LoadedBlock, BlockPositionCompare>::iterator i;
        for(i = m_pBlocks.begin(); i != m_pBlocks.end(); i++)
        {
            //Inaccurate - account for rest of loaded block.
            uSizeInBytes += i->second.block.calculateSizeInBytes();
        }

        //Memory used by the block cache.
        uSizeInBytes += m_vecUncompressedBlockCache.capacity() * sizeof(LoadedBlock);
        uSizeInBytes += m_vecUncompressedBlockCache.size() * m_uBlockSideLength * m_uBlockSideLength * m_uBlockSideLength * sizeof(VoxelType);

        return uSizeInBytes;
    }

}