polyvox/library/PolyVoxCore/include/PolyVoxCore/LargeVolume.inl

/*******************************************************************************
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/ConstVolumeProxy.h"
#include "PolyVoxImpl/Block.h"
#include "PolyVoxCore/Log.h"
#include "PolyVoxCore/Region.h"
#include "PolyVoxCore/Vector.h"

#include <limits>
#include <cassert>
#include <cstdlib> //For abort()
#include <cstring> //For memcpy
#include <list>
#include <stdexcept> //For invalid_argument

namespace PolyVox
{
	////////////////////////////////////////////////////////////////////////////////
	/// When construncting a very large volume you need to be prepared to handle the scenario where there is so much data that PolyVox cannot fit it all in memory. When PolyVox runs out of memory, it identifies the least recently used data and hands it back to the application via a callback function. It is then the responsibility of the application to store this data until PolyVox needs it again (as signalled by another callback function). Please see the LargeVolume  class documentation for a full description of this process and the required function signatures. If you really don't want to handle these events then you can provide null pointers here, in which case the data will be discarded and/or filled with default values.
	/// \param dataRequiredHandler The callback function which will be called when PolyVox tries to use data which is not currently in momory.
	/// \param dataOverflowHandler The callback function which will be called when PolyVox has too much data and needs to remove some from memory.
	/// \param uBlockSideLength The size of the blocks making up the volume. Small blocks will compress/decompress faster, but there will also be more of them meaning voxel access could be slower.
	////////////////////////////////////////////////////////////////////////////////
	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
	)
	{
		m_funcDataRequiredHandler = dataRequiredHandler;
		m_funcDataOverflowHandler = dataOverflowHandler;
		m_bPagingEnabled = true;
		//Create a volume of the right size.
		resize(Region::MaxRegion,uBlockSideLength);
	}

	////////////////////////////////////////////////////////////////////////////////
	/// Deprecated - do not use this constructor.
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	LargeVolume<VoxelType>::LargeVolume
	(
		int32_t dont_use_this_constructor_1, int32_t dont_use_this_constructor_2, int32_t dont_use_this_constructor_3
	)
	{
		//In earlier verions of PolyVox the constructor took three values indicating width, height, and depth. However, this
		//causes confusion because these three parameters can be interpreted as two function pointers and a block size instead,
		//hence calling a different constructor. And simply removing this constructor will cause confusion because existing
		//code with three parameters will then always resolve to the constructor with two function pointers and a block size.
		//
		//Eventually this constructor will be removed, it's just here to make people change their code to the new version.
		//
		//IF YOU HIT THIS ASSERT/ABORT, CHANGE YOUR CODE TO USE THE CONSTRUCTOR TAKING A 'Region' INSTEAD.
		assert(false);
		abort();
	}

	////////////////////////////////////////////////////////////////////////////////
	/// This constructor creates a volume with a fixed size which is specified as a parameter. By default this constructor will not enable paging but you can override this if desired. If you do wish to enable paging then you are required to provide the call back function (see the other LargeVolume constructor).
	/// \param regValid Specifies the minimum and maximum valid voxel positions.
	/// \param dataRequiredHandler The callback function which will be called when PolyVox tries to use data which is not currently in momory.
	/// \param dataOverflowHandler The callback function which will be called when PolyVox has too much data and needs to remove some from memory.
	/// \param bPagingEnabled Controls whether or not paging is enabled for this LargeVolume.
	/// \param uBlockSideLength The size of the blocks making up the volume. Small blocks will compress/decompress faster, but there will also be more of them meaning voxel access could be slower.
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	LargeVolume<VoxelType>::LargeVolume
	(
		const Region& regValid,
		polyvox_function<void(const ConstVolumeProxy<VoxelType>&, const Region&)> dataRequiredHandler,
		polyvox_function<void(const ConstVolumeProxy<VoxelType>&, const Region&)> dataOverflowHandler,
		bool bPagingEnabled,
		uint16_t uBlockSideLength
	)
	{
		m_funcDataRequiredHandler = dataRequiredHandler;
		m_funcDataOverflowHandler = dataOverflowHandler;
		m_bPagingEnabled = bPagingEnabled;

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

	////////////////////////////////////////////////////////////////////////////////
	/// Destroys the volume The destructor will call flushAll() to ensure that a paging volume has the chance to save it's data via the dataOverflowHandler() if desired.
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	LargeVolume<VoxelType>::~LargeVolume()
	{
		flushAll();
	}

	////////////////////////////////////////////////////////////////////////////////
	/// The border value is returned whenever an atempt is made to read a voxel which
	/// is outside the extents of the volume.
	/// \return The value used for voxels outside of the volume
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	VoxelType LargeVolume<VoxelType>::getBorderValue(void) const
	{
		return *m_pUncompressedBorderData;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// \return A Region representing the extent of the volume.
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	Region LargeVolume<VoxelType>::getEnclosingRegion(void) const
	{
		return m_regValidRegion;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// \return The width of the volume in voxels. Note that this value is inclusive, so that if the valid range is e.g. 0 to 63 then the width is 64.
	/// \sa getHeight(), getDepth()
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	int32_t LargeVolume<VoxelType>::getWidth(void) const
	{
		return m_regValidRegion.getUpperCorner().getX() - m_regValidRegion.getLowerCorner().getX() + 1;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// \return The height of the volume in voxels. Note that this value is inclusive, so that if the valid range is e.g. 0 to 63 then the height is 64.
	/// \sa getWidth(), getDepth()
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	int32_t LargeVolume<VoxelType>::getHeight(void) const
	{
		return m_regValidRegion.getUpperCorner().getY() - m_regValidRegion.getLowerCorner().getY() + 1;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// \return The depth of the volume in voxels. Note that this value is inclusive, so that if the valid range is e.g. 0 to 63 then the depth is 64.
	/// \sa getWidth(), getHeight()
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	int32_t LargeVolume<VoxelType>::getDepth(void) const
	{
		return m_regValidRegion.getUpperCorner().getZ() - m_regValidRegion.getLowerCorner().getZ() + 1;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// \return The length of the shortest side in voxels. For example, if a volume has
	/// dimensions 256x512x1024 this function will return 256.
	/// \sa getLongestSideLength(), getDiagonalLength()
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	int32_t LargeVolume<VoxelType>::getShortestSideLength(void) const
	{
		return m_uShortestSideLength;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// \return The length of the longest side in voxels. For example, if a volume has
	/// dimensions 256x512x1024 this function will return 1024.
	/// \sa getShortestSideLength(), getDiagonalLength()
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	int32_t LargeVolume<VoxelType>::getLongestSideLength(void) const
	{
		return m_uLongestSideLength;
	}	

	////////////////////////////////////////////////////////////////////////////////
	/// \return The length of the diagonal in voxels. For example, if a volume has
	/// dimensions 256x512x1024 this function will return sqrt(256*256+512*512+1024*1024)
	/// = 1173.139. This value is computed on volume creation so retrieving it is fast.
	/// \sa getShortestSideLength(), getLongestSideLength()
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	float LargeVolume<VoxelType>::getDiagonalLength(void) const
	{
		return m_fDiagonalLength;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// \param uXPos The \c x position of the voxel
	/// \param uYPos The \c y position of the voxel
	/// \param uZPos The \c z position of the voxel
	/// \return The voxel value
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	VoxelType LargeVolume<VoxelType>::getVoxelAt(int32_t uXPos, int32_t uYPos, int32_t uZPos) const
	{
		if(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 = 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);

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

	////////////////////////////////////////////////////////////////////////////////
	/// \param v3dPos The 3D position of the voxel
	/// \return The voxel value
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	VoxelType LargeVolume<VoxelType>::getVoxelAt(const Vector3DInt32& v3dPos) const
	{
		return getVoxelAt(v3dPos.getX(), v3dPos.getY(), v3dPos.getZ());
	}

	////////////////////////////////////////////////////////////////////////////////
	/// Enabling compression allows significantly more data to be stored in memory.
	/// \param bCompressionEnabled Specifies whether compression is enabled.
	////////////////////////////////////////////////////////////////////////////////	
	template <typename VoxelType>
	void LargeVolume<VoxelType>::setCompressionEnabled(bool bCompressionEnabled)
	{
		//Early out - nothing to do
		if(m_bCompressionEnabled == bCompressionEnabled)
		{
			return;
		}
		
		m_bCompressionEnabled = bCompressionEnabled;

		if(m_bCompressionEnabled)
		{
			//If compression has been enabled then we need to start honouring the max number of
			//uncompressed blocks. Because compression has been disabled for a while we might have
			//gone above that limit. Easiest solution is just to clear the cache and start again.
			clearBlockCache();
		}
	}

	////////////////////////////////////////////////////////////////////////////////
	/// Increasing the size of the block cache will increase memory but may improve performance.
	/// You may want to set this to a large value (e.g. 1024) when you are first loading your
	/// volume data and then set it to a smaller value (e.g.64) for general processing.
	/// \param uBlockCacheSize The number of blocks for which uncompressed data can be cached.
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	void LargeVolume<VoxelType>::setMaxNumberOfUncompressedBlocks(uint32_t uMaxNumberOfUncompressedBlocks)
	{
		clearBlockCache();

		m_uMaxNumberOfUncompressedBlocks = uMaxNumberOfUncompressedBlocks;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// Increasing the number of blocks in memory causes fewer calls to dataRequiredHandler()/dataOverflowHandler()
	/// \param uMaxBlocks The number of blocks
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	void LargeVolume<VoxelType>::setMaxNumberOfBlocksInMemory(uint32_t uMaxNumberOfBlocksInMemory)
	{
		if(m_pBlocks.size() > uMaxNumberOfBlocksInMemory)
		{
			flushAll();
		}
		m_uMaxNumberOfBlocksInMemory  = uMaxNumberOfBlocksInMemory;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// \param tBorder The value to use for voxels outside the volume.
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	void LargeVolume<VoxelType>::setBorderValue(const VoxelType& tBorder) 
	{
		/*Block<VoxelType>* pUncompressedBorderBlock = getUncompressedBlock(&m_pBorderBlock);
		return pUncompressedBorderBlock->fill(tBorder);*/
		std::fill(m_pUncompressedBorderData, m_pUncompressedBorderData + m_uBlockSideLength * m_uBlockSideLength * m_uBlockSideLength, tBorder);
	}

	////////////////////////////////////////////////////////////////////////////////
	/// \param uXPos the \c x position of the voxel
	/// \param uYPos the \c y position of the voxel
	/// \param uZPos the \c z position of the voxel
	/// \param tValue the value to which the voxel will be set
	/// \return whether the requested position is inside the volume
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	bool LargeVolume<VoxelType>::setVoxelAt(int32_t uXPos, int32_t uYPos, int32_t uZPos, VoxelType tValue)
	{
		assert(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 = 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;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// \param v3dPos the 3D position of the voxel
	/// \param tValue the value to which the voxel will be set
	/// \return whether the requested position is inside the volume
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	bool LargeVolume<VoxelType>::setVoxelAt(const Vector3DInt32& v3dPos, VoxelType tValue)
	{
		return setVoxelAt(v3dPos.getX(), v3dPos.getY(), v3dPos.getZ(), tValue);
	}


	////////////////////////////////////////////////////////////////////////////////
	/// Note that if MaxNumberOfBlocksInMemory is not large enough to support the region this function will only load part of the region. In this case it is undefined which parts will actually be loaded. If all the voxels in the given region are already loaded, this function will not do anything. Other voxels might be unloaded to make space for the new voxels.
	/// \param regPrefetch The Region of voxels to prefetch into memory.
	////////////////////////////////////////////////////////////////////////////////
	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>::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
	}

	////////////////////////////////////////////////////////////////////////////////
	/// Removes all voxels from memory, and calls dataOverflowHandler() to ensure the application has a chance to store the data.
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	void LargeVolume<VoxelType>::flushAll()
	{
		typename std::map<Vector3DInt32, LoadedBlock >::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());
		}
	}

	////////////////////////////////////////////////////////////////////////////////
	/// Removes all voxels in the specified Region from memory, and calls dataOverflowHandler() to ensure the application has a chance to store the data. It is possible that there are no voxels loaded in the Region, in which case the function will have no effect.
	////////////////////////////////////////////////////////////////////////////////
	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>::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_vecUncompressedBlockCache.clear();
	}

	////////////////////////////////////////////////////////////////////////////////
	/// This function should probably be made internal...
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	void LargeVolume<VoxelType>::resize(const Region& regValidRegion, uint16_t uBlockSideLength)
	{
		//Debug mode validation
		assert(uBlockSideLength > 0);
		
		//Release mode validation
		if(uBlockSideLength == 0)
		{
			throw std::invalid_argument("Block side length cannot be zero.");
		}
		if(!isPowerOf2(uBlockSideLength))
		{
			throw std::invalid_argument("Block side length must be a power of two.");
		}

		m_uTimestamper = 0;
		m_uMaxNumberOfUncompressedBlocks = 16;
		m_uBlockSideLength = uBlockSideLength;
		m_pUncompressedBorderData = 0;
		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;
		m_bCompressionEnabled = true;

		m_regValidRegion = regValidRegion;

		m_regValidRegionInBlocks.setLowerCorner(m_regValidRegion.getLowerCorner()  / static_cast<int32_t>(uBlockSideLength));
		m_regValidRegionInBlocks.setUpperCorner(m_regValidRegion.getUpperCorner()  / static_cast<int32_t>(uBlockSideLength));

		setMaxNumberOfUncompressedBlocks(m_uMaxNumberOfUncompressedBlocks);

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

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

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

		//Create the border block
		m_pUncompressedBorderData = new VoxelType[m_uBlockSideLength * m_uBlockSideLength * m_uBlockSideLength];
		std::fill(m_pUncompressedBorderData, m_pUncompressedBorderData + m_uBlockSideLength * m_uBlockSideLength * m_uBlockSideLength, VoxelType());

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

	template <typename VoxelType>
	void LargeVolume<VoxelType>::eraseBlock(typename std::map<Vector3DInt32, LoadedBlock >::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_bCompressionEnabled) {
			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();
					// 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))
		{
			assert(m_pLastAccessedBlock->m_tUncompressedData);
			return m_pLastAccessedBlock;
		}		

		typename std::map<Vector3DInt32, LoadedBlock >::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 >::iterator i;
					typename std::map<Vector3DInt32, LoadedBlock >::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);
			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)
		{ 			
			assert(m_pLastAccessedBlock->m_tUncompressedData);
			return m_pLastAccessedBlock;
		}

		//If we are allowed to compress then check whether we need to
		if((m_bCompressionEnabled) && (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();

			//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_pLastAccessedBlock = &(loadedBlock.block);
		assert(m_pLastAccessedBlock->m_tUncompressedData);
		return m_pLastAccessedBlock;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// Note: This function needs reviewing for accuracy...
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	float LargeVolume<VoxelType>::calculateCompressionRatio(void)
	{
		float fRawSize = m_pBlocks.size() * m_uBlockSideLength * m_uBlockSideLength* m_uBlockSideLength * sizeof(VoxelType);
		float fCompressedSize = calculateSizeInBytes();
		return fCompressedSize/fRawSize;
	}

	////////////////////////////////////////////////////////////////////////////////
	/// Note: This function needs reviewing for accuracy...
	////////////////////////////////////////////////////////////////////////////////
	template <typename VoxelType>
	uint32_t LargeVolume<VoxelType>::calculateSizeInBytes(void)
	{
		uint32_t uSizeInBytes = sizeof(LargeVolume);

		//Memory used by the blocks
		typename std::map<Vector3DInt32, LoadedBlock >::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);

		//Memory used by border data.
		if(m_pUncompressedBorderData)
		{
			uSizeInBytes += m_uBlockSideLength * m_uBlockSideLength * m_uBlockSideLength * sizeof(VoxelType);
		}

		return uSizeInBytes;
	}

}