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#ifndef __ANCESTORGRID_H
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#define __ANCESTORGRID_H
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#include "CGLA/Vec3i.h"
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namespace Geometry
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{
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/** This class template is used as abstract ancestor of
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voxel grids. Strictly speaking, this class is not
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abstract, since it does not have any virtual functions.
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However, operator[]() and store() simply call
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functions in derived classes. To do so, you must pass
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the derived class as a template argument to this class
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when you define the derived class. This is called the
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Barton and Nackman trick. See Todd Veldhuizen,
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"Techniques for Scientific C++" 1.3.3.
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*/
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template<typename T, class ChildT>
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class AncestorGrid
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{
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public:
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typedef T DataType;
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private:
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/// xyz dimensions of grid.
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CGLA::Vec3i dims;
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public:
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/// Construct a grid of specified xyz dimensions.
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AncestorGrid(int _x_dim, int _y_dim, int _z_dim):
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dims(_x_dim,_y_dim,_z_dim) {}
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/// Construct a grid of specified xyz dimensions.
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AncestorGrid(const CGLA::Vec3i& _dims): dims(_dims) {}
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/** Check if voxel is within grid bounds.
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This function is passed a Vec3i, p, and returns true
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if p is within the voxel grid. */
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bool in_domain(const CGLA::Vec3i& p) const
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{
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for(int i=0; i<3; i++)
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if (p[i]<0 || p[i] >= dims[i])
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return false;
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return true;
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}
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/** Get dimensions of grid.
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This function returns a Vec3i with the dimensions
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of the grid. */
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const CGLA::Vec3i& get_dims() const {return dims;}
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/** Get the corner having smallest coordinates */
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const CGLA::Vec3i get_lo_corner() const {return CGLA::Vec3i(0);}
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/** Get the corner having greatest coordinates. */
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const CGLA::Vec3i& get_hi_corner() const {return dims;}
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/** Access (read only) a voxel in a grid.
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This is the operator[] which is passed a Vec3i
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and returns a const reference to a voxel.
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This function is "statically virtual", i.e.
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it simply calls the store function of a derived
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class.
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See below why there is no non-const operator[]
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*/
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const T& operator[](const CGLA::Vec3i& p) const
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{
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return static_cast<const ChildT&>(*this)[p];
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}
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/** Store a voxel in grid.
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This function returns nothing but is passed a
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Vec3i p and T value t and stores t at p in the
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grid. This function is "statically virtual", i.e.
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it simply calls the store function of a derived
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class.
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Yes, it would be simpler to provide a non-const
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operator[], however, a non-const operator[] will
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often be called even when no writing takes place.
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(Scott Meyers, "More Effective C++, p. 218)
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If a grid implementation allocates memory when
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a voxel is accessed for writing, then it is a problem
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that we cannot be sure a non-const operator[] is
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called only if we are writing. We might then allocate
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memory even if we just want to read.
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*/
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void store(const CGLA::Vec3i& p, const T& t)
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{
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return static_cast<ChildT&>(*this).store(p,t);
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}
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void clear()
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{
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return static_cast<ChildT&>(*this).clear();
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}
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};
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}
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#endif
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