194 lines
8.4 KiB
C++
194 lines
8.4 KiB
C++
#pragma region License
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/******************************************************************************
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This file is part of the PolyVox library
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Copyright (C) 2006 David Williams
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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as published by the Free Software Foundation; either version 2
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of the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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******************************************************************************/
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#pragma endregion
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#ifndef __PolyVox_Volume_H__
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#define __PolyVox_Volume_H__
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#pragma region Headers
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#include "PolyVoxImpl/Block.h"
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#include "PolyVoxForwardDeclarations.h"
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#include "PolyVoxImpl/CPlusPlusZeroXSupport.h"
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#include <limits>
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#include <map>
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#include <vector>
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#pragma endregion
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namespace PolyVox
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{
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///The Volume class provides a memory efficient method of storing voxel data while also allowing fast access and modification.
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/*******************************************************************************
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A Volume is essentially a '3D image' in which each element (voxel) is identified
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by a three dimensional (x,y,z) coordinate, rather than the two dimensional (x,y)
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coordinate which is used to identify an element (pixel) in a normal image. Within
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PolyVox, the Volume class is used to store and manipulate our data before we extract
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our SurfacePatch's from it.
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<b>Data Representaion - feel free to skip</b>
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If stored carelessly, volume data can take up a huge amount of memory. For example, a
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volume of dimensions 1024x1024x1024 with 1 byte per voxel will require 1GB of memory
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if stored in an uncompressed form. Natuarally our Volume class is much more efficient
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than this and it is worth understanding (at least at a high level) the approach
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which is used.
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Essentially, the Volume class stores its data as a collection of blocks. Each
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of these block is much smaller than the whole volume, for example a typical size
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might be 32x32x32 voxels (though is is configurable by the user). In this case,
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a 256x512x1024 volume would contain 8x16x32 = 4096 blocks. However, it is unlikely that
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all these blocks actually have to be stored because usually there are duplicates
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in which case common data can be shared.
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Identifying duplicate blocks is in general a difficult task which involves looking at pairs
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of blocks and comparing all the voxels. This is a time consuming task which is not amiable
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to being performed when the volume is being modified in real time. However, there are two
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specific scenarios which are easily spotted and which PolyVox uses to identify block
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sharing opportunities.
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-# Homogeneous blocks (those which contain just a single voxel value) are easy to
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spot and fairly common becuase volumes often contain large homogeous regions. Any time
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you change the value of a voxel you have potentially made the block which contains
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it homogeneous. PolyVox does not check the homogeneity immediatly as this would slow
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down the process of modifying voxels, but you can use the tidyUpMemory() function
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to check for and remove duplicate homogeneous regions whenever you have spare
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processing time.
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-# Copying a volume naturally means that all the voxels in the second voluem are
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the same as the first. Therefore volume copying is a relatively fast operation in
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which all the blocks in the second volume simply reference the first volume. Future
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modifications to either volume will, of course, cause the blocks to become unshared.
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Other advantages of breaking the volume down into blocks include enhancing data locality
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(i.e. voxels which are spatially near to each other are also likely to be near in
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memory) and the ability to load larger volumes as no large contiguous areas of
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memory are needed. However, these advantages are more transparent to user code
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so we will not dwell on them here.
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<b>Usage</b>
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Volumes are constructed by passing the desired width height and depth to the
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constructor. Note that for speed reasons only values which are a power of two
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are permitted for these sidelengths.
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Access to specific voxels is provided by the getVoxelAt() and setVoxelAt fuctions.
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Each of these has two forms so that voxels can be identified by integer triples
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or by Vector3DUint16's.
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The tidyUpMemory() function should normally be called after you first populate
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the volume with data, and then at periodic intervals as the volume is modified.
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However, you don't actually <i>have</i> to call it at all. See the functions
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documentation for further details.
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One further important point of note is that this class is templatised on the voxel
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type. This allows you to store volumes of data types you might not normally expect,
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for example theOpenGL example 'abuses' this class to store a 3D grid of pointers.
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However, it is not guarentted that all functionality works correctly with non-integer
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voxel types.
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*******************************************************************************/
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template <typename VoxelType>
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class Volume
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{
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//Make VolumeIterator a friend
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friend class VolumeIterator<VoxelType>;
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public:
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///Constructor
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Volume(uint16_t uWidth, uint16_t uHeight, uint16_t uDepth, uint16_t uBlockSideLength = 64);
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///Destructor
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~Volume();
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///Gets a Region representing the extents of the Volume.
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Region getEnclosingRegion(void) const;
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///Gets the width of the volume in voxels.
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uint16_t getWidth(void) const;
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///Gets the height of the volume in voxels.
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uint16_t getHeight(void) const;
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///Gets the depth of the volume in voxels.
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uint16_t getDepth(void) const;
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///Gets the length of the longest side in voxels
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uint16_t getLongestSideLength(void) const;
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///Gets the length of the shortest side in voxels
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uint16_t getShortestSideLength(void) const;
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///Gets the length of the diagonal in voxels
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float getDiagonalLength(void) const;
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VoxelType getVoxelAt(uint16_t uXPos, uint16_t uYPos, uint16_t uZPos) const;
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VoxelType getVoxelAt(const Vector3DUint16& v3dPos) const;
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void setVoxelAt(uint16_t uXPos, uint16_t uYPos, uint16_t uZPos, VoxelType tValue);
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void setVoxelAt(const Vector3DUint16& v3dPos, VoxelType tValue);
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void tidyUpMemory(uint32_t uNoOfBlocksToProcess = (std::numeric_limits<uint32_t>::max)());
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bool isRegionHomogenous(const Region& region);
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private:
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POLYVOX_SHARED_PTR< Block<VoxelType> > getHomogenousBlock(VoxelType tHomogenousValue) const;
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std::vector< POLYVOX_SHARED_PTR< Block<VoxelType> > > m_pBlocks;
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std::vector<bool> m_vecBlockIsPotentiallyHomogenous;
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//Note: We were once storing weak_ptr's in this map, so that the blocks would be deleted once they
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//were not being referenced by anyone else. However, this made it difficult to know when a block was
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//shared. A call to shared_ptr::unique() from within setVoxel was not sufficient as weak_ptr's did
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//not contribute to the reference count. Instead we store shared_ptr's here, and check if they
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//are used by anyone else (i.e are non-unique) when we tidy the volume.
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//FIXME - How do we handle sharing between two volumes with different block sizes?!
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static std::map<VoxelType, POLYVOX_SHARED_PTR< Block<VoxelType> > > m_pHomogenousBlock;
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uint32_t m_uNoOfBlocksInVolume;
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uint16_t m_uWidthInBlocks;
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uint16_t m_uHeightInBlocks;
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uint16_t m_uDepthInBlocks;
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uint16_t m_uWidth;
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uint8_t m_uWidthPower;
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uint16_t m_uHeight;
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uint8_t m_uHeightPower;
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uint16_t m_uDepth;
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uint8_t m_uDepthPower;
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uint8_t m_uBlockSideLengthPower;
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uint16_t m_uBlockSideLength;
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uint16_t m_uLongestSideLength;
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uint16_t m_uShortestSideLength;
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float m_fDiagonalLength;
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uint32_t m_uCurrentBlockForTidying;
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};
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//Required for the static member
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template <class VoxelType> std::map<VoxelType, POLYVOX_SHARED_PTR< Block<VoxelType> > > Volume<VoxelType>::m_pHomogenousBlock;
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//Some handy typedefs
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typedef Volume<float> FloatVolume;
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typedef Volume<uint8_t> UInt8Volume;
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typedef Volume<uint16_t> UInt16Volume;
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}
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#include "Volume.inl"
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#endif
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