mpri-graphics-project/MarchingCubes.hpp

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#pragma once
/** Implement the Marching Cubes algorithm
*
* Marching cubes:
* W. E. Lorensen, H. E. Cline, 1987
* ``Marching cubes: a high resulution 3D surface construction algorithm''
* <http://fab.cba.mit.edu/classes/S62.12/docs/Lorensen_marching_cubes.pdf>
*/
#include <vector>
#include <set>
#include "Mesh.hpp"
#include "Implicit.hpp"
#include "common_structures.hpp"
class MarchingCubes {
private:
typedef std::set<PointLoc> LocSet;
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class Intersections {
public:
typedef unsigned char intersect_t;
Intersections() : inters(0) {}
intersect_t value() const {
return inters;
}
/** The corners are indexed with three booleans, one for each
* axis (x, y, z). A false value means a lower coordinate along
* this axis.
* Eg., (false, true, false) means the corner (0, 1, 0) for a
* cube of side 1 placed at (0, 0, 0).
*/
void set_corner(bool x, bool y, bool z, bool val) {
intersect_t mask = 1 << (shift(x, y, z));
if(val)
inters |= mask;
else
inters &= ~mask;
}
bool get_corner(bool x, bool y, bool z) const {
return (inters & (1 << shift(x, y, z))) == 1;
}
private:
intersect_t inters;
int shift(bool x, bool y, bool z) const {
return x + (y << 1) + (z << 2);
}
};
public:
MarchingCubes(
const ImplicitSurface& surface,
const Cuboid& box=Cuboid(
Point(-20, -20, -20),
Point(20, 20, 20)),
double resolution=.25);
/** Add a starting point hint
*
* A hint is a cuboid that should intersect at least once the surface,
* such that the marching cube will find the surface there and will be
* able to follow it.
* If at least a hint is given, the algorithm will expect that at least
* a hint per disjoint surface is given, ie. that it is safe to only
* follow the surface starting from the hints, and ignoring the parts
* of the grid that are "far" from the hints.
*/
void add_hint(const Cuboid& hint);
Mesh operator()();
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struct CubeEdge {
CubeEdge() {}
CubeEdge(bool x0, bool y0, bool z0,
bool x1, bool y1, bool z1)
{
x[0] = x0;
y[0] = y0;
z[0] = z0;
x[1] = x1;
y[1] = y1;
z[1] = z1;
}
bool x[2], y[2], z[2];
bool operator==(const CubeEdge& oth) const {
return x[0] == oth.x[0] && x[1] == oth.x[1]
&& y[0] == oth.y[0] && y[1] == oth.y[1]
&& z[0] == oth.z[0] && z[1] == oth.z[1];
}
/** Get the space point at a given position of [0,1] along the edge
* when the base of the cube (ie. (0, 0, 0)) is given. */
Point at(double pos,
double bx, double by, double bz, double resolution) const;
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};
struct CubeTri {
CubeTri() {}
CubeTri(const CubeEdge* edge_) {
for(size_t i=0; i < 3; ++i)
edge[i] = edge_[i];
}
CubeTri(const CubeEdge e0, const CubeEdge e1, const CubeEdge e2) {
edge[0] = e0;
edge[1] = e1;
edge[2] = e2;
}
CubeEdge edge[3];
};
private: //methods
bool march_at(double x, double y, double z, Mesh& output);
/// ^ Adds triangles for the given location. Returns true if any
/// triangle was added.
void without_hints(Mesh& output);
Intersections mk_intersection_cube(double bx, double by, double bz,
double side_len) const;
Point intersect_location(const CubeEdge& edge,
double bx, double by, double bz) const;
private:
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static const std::vector<CubeTri> edges_of_intersection[256];
const ImplicitSurface& surface;
Cuboid box;
double resolution;
std::vector<Cuboid> hints;
};