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