154 lines
6.9 KiB
C++
154 lines
6.9 KiB
C++
/*******************************************************************************
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Copyright (c) 2005-2009 David Williams
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This software is provided 'as-is', without any express or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it
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freely, subject to the following restrictions:
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1. The origin of this software must not be misrepresented; you must not
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claim that you wrote the original software. If you use this software
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in a product, an acknowledgment in the product documentation would be
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appreciated but is not required.
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2. Altered source versions must be plainly marked as such, and must not be
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misrepresented as being the original software.
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3. This notice may not be removed or altered from any source
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distribution.
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*******************************************************************************/
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#ifndef __PolyVox_MarchingCubesController_H__
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#define __PolyVox_MarchingCubesController_H__
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#include "PolyVoxCore/BaseVolume.h"
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#include <limits>
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namespace PolyVox
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{
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/**
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* This class provides a default implementation of a controller for the MarchingCubesSurfaceExtractor. It controls the behaviour of the
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* MarchingCubesSurfaceExtractor and provides the required properties from the underlying voxel type.
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*
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* PolyVox does not enforce any requirements regarding what data must be present in a voxel, and instead allows any primitive or user-defined
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* type to be used. However, the Marching Cubes algorithm does have some requirents about the underlying data in that conceptually it operates
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* on a <i>density field</i>. In addition, the PolyVox implementation of the Marching Cubes algorithm also understands the idea of each voxel
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* having a material which is copied into the vertex data.
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*
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* Because we want the MarchingCubesSurfaceExtractor to work on <i>any</i> voxel type, we use a <i>Marching Cubes controller</i> (passed as
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* a parameter of the MarchingCubesSurfaceExtractor) to expose the required properties. This parameter defaults to the DefaultMarchingCubesController.
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* The main implementation of this class is designed to work with primitives data types, and the class is also specialised for the Material,
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* Density and MaterialdensityPair classes.
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*
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* If you create a custom class for your voxel data then you probably want to include a specialisation of DefaultMarchingCubesController,
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* though you don't have to if you don't want to use the Marching Cubes algorithm or if you prefer to define a seperate Marching Cubes controller
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* and pass it as an explicit parameter (rather than relying on the default).
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*
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* For primitive types, the DefaultMarchingCubesController considers the value of the voxel to represent it's density and just returns a constant
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* for the material. So you can, for example, run the MarchingCubesSurfaceExtractor on a volume of floats or ints.
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*
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* It is possible to customise the behaviour of the controller by providing a threshold value through the constructor. The extracted surface
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* will pass through the density value specified by the threshold, and so you should make sure that the threshold value you choose is between
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* the minimum and maximum values found in your volume data. By default it is in the middle of the representable range of the underlying type.
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*
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* \sa MarchingCubesSurfaceExtractor
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*
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*/
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template<typename VoxelType>
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class DefaultMarchingCubesController
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{
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public:
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/// Used to inform the MarchingCubesSurfaceExtractor about which type it should use for representing densities.
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typedef VoxelType DensityType;
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/// Used to inform the MarchingCubesSurfaceExtractor about which type it should use for representing materials.
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typedef VoxelType MaterialType;
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/**
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* Constructor
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*
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* This version of the constructor takes no parameters and sets the threshold to the middle of the representable range of the underlying type.
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* For example, if the voxel type is 'uint8_t' then the representable range is 0-255, and the threshold will be set to 127. On the other hand,
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* if the voxel type is 'float' then the representable range is -FLT_MAX to FLT_MAX and the threshold will be set to zero.
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*/
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DefaultMarchingCubesController(void)
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{
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if (std::is_signed<DensityType>())
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{
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m_tThreshold = DensityType(0);
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}
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else
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{
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m_tThreshold = (((std::numeric_limits<DensityType>::min)() + (std::numeric_limits<DensityType>::max)()) / 2);
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}
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}
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/**
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* Converts the underlying voxel type into a density value.
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*
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* The default implementation of this function just returns the voxel type directly and is suitable for primitives types. Specialisations of
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* this class can modify this behaviour.
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*/
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DensityType convertToDensity(VoxelType voxel)
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{
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return voxel;
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}
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/**
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* Converts the underlying voxel type into a material value.
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*
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* The default implementation of this function just returns the constant '1'. There's not much else it can do, as it needs to work with primitive
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* types and the actual value of the type is already being considered to be the density. Specialisations of this class can modify this behaviour.
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*/
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MaterialType convertToMaterial(VoxelType /*voxel*/)
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{
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return 1;
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}
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/**
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* Returns a material which is in some sense a weighted combination of the supplied materials.
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*
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* The Marching Cubes algotithm generates vertices which lie between voxels, and ideally the material of the vertex should be interpolated from the materials
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* of the voxels. In practice, that material type is often an integer identifier (e.g. 1 = rock, 2 = soil, 3 = grass) and an interpolation doean't make sense
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* (e.g. soil is not a combination or rock and grass). Therefore this default interpolation just returns whichever material is associated with a voxel of the
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* higher density, but if more advanced voxel types do support interpolation then it can be implemented in this function.
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*/
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MaterialType blendMaterials(VoxelType a, VoxelType b, float /*weight*/)
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{
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if(convertToDensity(a) > convertToDensity(b))
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{
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return convertToMaterial(a);
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}
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else
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{
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return convertToMaterial(b);
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}
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}
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/**
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* Returns the density value which was passed to the constructor.
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*
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* As mentioned in the class description, the extracted surface will pass through the density value specified by the threshold, and so you
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* should make sure that the threshold value you choose is between the minimum and maximum values found in your volume data. By default it
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* is in the middle of the representable range of the underlying type.
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*/
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DensityType getThreshold(void)
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{
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return m_tThreshold;
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}
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void setThreshold(DensityType tThreshold)
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{
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m_tThreshold = tThreshold;
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}
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private:
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DensityType m_tThreshold;
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};
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}
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#endif
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