149 lines
4.3 KiB
C++
149 lines
4.3 KiB
C++
#include "MarchingCubes.hpp"
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#include <cassert>
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MarchingCubes::MarchingCubes(
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const ImplicitSurface& surface,
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const Cuboid& box,
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double resolution):
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surface(surface),
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box(box),
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resolution(resolution)
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{}
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void MarchingCubes::add_hint(const Cuboid& hint) {
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hints.push_back(hint);
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}
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Mesh MarchingCubes::operator()() {
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Mesh output;
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without_hints(output);
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output.translate(surface.getCenter());
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return output;
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}
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void MarchingCubes::without_hints(Mesh& output) {
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for(double x = box.low(0); x < box.high(0) + resolution;
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x += resolution) {
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for(double y = box.low(1); y < box.high(1) + resolution;
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y += resolution) {
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for(double z = box.low(2); z < box.high(2) + resolution;
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z += resolution) {
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march_at(x, y, z, output);
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}
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}
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}
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}
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Point MarchingCubes::CubeEdge::at(double pos,
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double bx, double by, double bz, double resolution) const
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{
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auto bary = [pos](double x, double y) {
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return pos * x + (1.-pos) * y;
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};
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Point p1(
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bx + x[0] * resolution,
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by + y[0] * resolution,
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bz + z[0] * resolution);
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Point p2(
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bx + x[1] * resolution,
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by + y[1] * resolution,
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bz + z[1] * resolution);
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return Point(
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bary(p1.x, p2.x),
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bary(p1.y, p2.y),
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bary(p1.z, p2.z));
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}
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bool MarchingCubes::march_at(double x, double y, double z, Mesh& output) {
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/* =====
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* NOTE: this code currently computes 8 times the surface value
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* at each corner point of the inspected space. This is okay
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* for now, because such computations are ultra light and
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* actually better than storing values.
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* If a time comes when this computation is heavier, because we
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* are looking at more complex implicit surfaces,
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* IT WILL BE NECESSARY TO ENHANCE THIS CODE!
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* ==== */
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Intersections intersections = mk_intersection_cube(x, y, z, resolution);
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const std::vector<CubeTri>& cur_triangles =
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edges_of_intersection[intersections.value()];
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for(const CubeTri& cube_tri: cur_triangles) {
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Point verts[3] = {
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intersect_location(cube_tri.edge[0],
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x, y, z),
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intersect_location(cube_tri.edge[1],
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x, y, z),
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intersect_location(cube_tri.edge[2],
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x, y, z),
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};
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size_t vert_ids[3];
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for(int i=0; i < 3; ++i)
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vert_ids[i] = output.add_vertice(verts[i]);
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for(int i=0; i < 3; ++i) {
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output.add_face(
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vert_ids[i],
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vert_ids[(i+1) % 3],
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vert_ids[(i+2) % 3]);
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}
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}
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return !cur_triangles.empty();
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}
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MarchingCubes::Intersections MarchingCubes::mk_intersection_cube(
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double bx, double by, double bz, double side_len) const
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{
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Intersections intersections;
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for(int dx=0; dx <= 1; dx++) {
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for(int dy=0; dy <= 1; dy++) {
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for(int dz=0; dz <= 1; dz++) {
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double cx = bx + side_len * dx;
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double cy = by + side_len * dy;
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double cz = bz + side_len * dz;
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intersections.set_corner(dx, dy, dz,
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surface(cx, cy, cz) > 0);
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}
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}
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}
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return intersections;
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}
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Point MarchingCubes::intersect_location(const CubeEdge& edge,
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double bx, double by, double bz) const
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{
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std::function<Point(double, double)> compute =
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[&](double low_prop, double high_prop)
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{
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double med_prop = (low_prop + high_prop) / 2;
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Point med = edge.at(med_prop, bx, by, bz, resolution),
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low = edge.at(low_prop, bx, by, bz, resolution),
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high = edge.at(high_prop, bx, by, bz, resolution);
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if(high_prop - low_prop < 1e-8)
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return med;
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double sLow = surface(low),
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sMed = surface(med),
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sHigh = surface(high);
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assert(sLow * sHigh <= 0);
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// ^ Can still binary search
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if(sLow * sMed <= 0)
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return compute(low_prop, med_prop);
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return compute(med_prop, high_prop);
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};
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return compute(0, 1);
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}
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