poission: add more thoroughly documented poisson sampler
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@ -15,57 +15,3 @@
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*/
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#include "sample.hpp"
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#include "../point.hpp"
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#include <random>
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///////////////////////////////////////////////////////////////////////////////
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std::vector<util::point2f>
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util::geom::poisson_sample (util::extent2i area, float distance, int samples)
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{
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std::vector<util::point2f> selected;
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std::vector<util::point2f> candidates (samples);
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std::uniform_real_distribution<float> dist_w (0, area.w);
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std::uniform_real_distribution<float> dist_h (0, area.h);
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std::random_device rd;
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std::default_random_engine gen;
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selected.push_back ({
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dist_w (gen),
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dist_h (gen),
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});
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auto min_distance = [&selected] (auto q) {
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float min_d = INFINITY;
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for (auto s: selected)
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if (auto s_d = util::distance2 (s, q); s_d < min_d)
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min_d = s_d;
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return min_d;
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};
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while (1) {
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util::point2f p;
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float d = -INFINITY;
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for (int i = 0; i < samples; ++i) {
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util::point2f candidate { dist_w (gen), dist_h (gen) };
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if (auto p_d = min_distance (candidate); p_d > d) {
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p = candidate;
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d = p_d;
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}
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}
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if (std::sqrt (d) < distance)
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break;
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selected.push_back (p);
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}
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return selected;
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}
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@ -77,6 +77,84 @@ namespace util::geom {
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std::vector<util::point2f>
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poisson_sample (util::extent2i, float distance, int samples);
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namespace surface {
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// a generator of samples that lie on the surface of a shape
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template <typename ShapeT>
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class sampler;
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template <typename ShapeT>
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sampler (ShapeT) -> sampler<std::decay_t<ShapeT>>;
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/// approximate a poisson disc sampling through mitchell's best candidate.
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///
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/// try to keep adding a new point to a set. each new point is the
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/// best of a set of candidates. the 'best' is the point that is
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/// furthest from all selected points.
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///
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/// \return a vector of the computed points
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template <typename SamplerT, typename GeneratorT>
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auto
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poisson (SamplerT const &target,
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GeneratorT &&gen,
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float minimum_distance,
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size_t candidates_count)
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{
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using point_type = decltype (target (gen));
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std::vector<point_type> selected;
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std::vector<point_type> candidates;
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// prime the found elements list with an initial point we can
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// perform distance calculations on
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selected.push_back (target (gen));
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// keep trying to add one more new point
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while (1) {
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// generate a group of candidate points
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candidates.clear ();
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std::generate_n (
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std::back_inserter (candidates),
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candidates_count,
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[&] (void) {
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return target (gen);
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}
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);
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// find the point whose minimum distance to the existing
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// points is the greatest (while also being greater than the
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// required minimum distance);
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float best_distance = -INFINITY;
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size_t best_index;
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for (size_t i = 0; i < candidates.size (); ++i) {
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auto const p = candidates[i];
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float d = INFINITY;
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// find the minimum distance from this candidate to the
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// selected points
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for (auto q: selected)
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d = util::min (d, distance (p, q));
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// record if it's the furthest away
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if (d > best_distance) {
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best_distance = d;
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best_index = i;
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}
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}
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// if we didn't find a suitable point then we give up and
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// return the points we found, otherwise record the best point
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if (best_distance < minimum_distance)
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break;
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selected.push_back (candidates[best_index]);
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}
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return selected;
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}
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}
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}
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#endif
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@ -1,20 +1,45 @@
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#include "cmdopt.hpp"
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#include "geom/sample.hpp"
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#include "geom/aabb.hpp"
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#include <cstdlib>
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#include <iostream>
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#include <random>
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template <size_t S>
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class util::geom::surface::sampler<util::extent<S,float>> {
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public:
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sampler (util::extent<S,float> _target):
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target (_target)
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{ ; }
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template <typename GeneratorT>
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util::point<S,float>
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operator() (GeneratorT &&gen) const noexcept
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{
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util::point<S,float> p;
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for (size_t i = 0; i < S; ++i)
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p[i] = std::uniform_real_distribution<float> (0, target[i]) (gen);
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return p;
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}
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private:
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util::extent<S,float> target;
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};
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///////////////////////////////////////////////////////////////////////////////
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int
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main (int argc, char **argv)
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{
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util::extent2i area {256, 256};
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util::extent2f area {256, 256};
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float distance = 5.f;
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int samples = 15;
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util::cmdopt::parser opts;
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opts.add<util::cmdopt::option::value<int>> ('w', "width", "width of the space to fill", area.w);
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opts.add<util::cmdopt::option::value<int>> ('h', "height", "height of the space to fill", area.h);
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opts.add<util::cmdopt::option::value<float>> ('w', "width", "width of the space to fill", area.w);
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opts.add<util::cmdopt::option::value<float>> ('h', "height", "height of the space to fill", area.h);
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opts.add<util::cmdopt::option::value<float>> ('d', "distance", "minimum distance between samples", distance);
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opts.add<util::cmdopt::option::value<int>> ('s', "samples", "number of samples per iteration", samples);
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@ -22,9 +47,15 @@ main (int argc, char **argv)
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std::cout << "<svg height='" << area.h << "' width='" << area.h << "'>";
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for (auto p: util::geom::poisson_sample (area, distance, samples))
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for (auto p: util::geom::surface::poisson (util::geom::surface::sampler (area),
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std::default_random_engine (),
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distance,
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samples))
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{
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std::cout << "<circle cx='" << p.x << "' cy='" << p.y << "' r='1' />";
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std::cout << "</svg>";
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}
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std::cout << "</svg>\n";
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return EXIT_SUCCESS;
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}
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