From 89defb3bc2c085b777752c4eb225f52ca5fa1251 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Thu, 19 Apr 2018 13:27:43 +1000
Subject: [PATCH] geom/sample: add trivial poisson sample generator

---
 CMakeLists.txt  |  1 +
 geom/sample.cpp | 71 +++++++++++++++++++++++++++++++++++++++++++++++++
 geom/sample.hpp |  9 +++++--
 3 files changed, 79 insertions(+), 2 deletions(-)
 create mode 100644 geom/sample.cpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 43aff927..6264d529 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -240,6 +240,7 @@ list (
     geom/ray.hpp
     geom/rect.cpp
     geom/rect.hpp
+    geom/sample.cpp
     geom/sample.hpp
     geom/sphere.cpp
     geom/sphere.hpp
diff --git a/geom/sample.cpp b/geom/sample.cpp
new file mode 100644
index 00000000..7663a71b
--- /dev/null
+++ b/geom/sample.cpp
@@ -0,0 +1,71 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2018 Danny Robson <danny@nerdcruft.net>
+ */
+
+#include "sample.hpp"
+
+#include "../point.hpp"
+
+#include <random>
+
+
+///////////////////////////////////////////////////////////////////////////////
+std::vector<util::point2f>
+util::geom::poisson_sample (util::extent2i area, float distance, int samples)
+{
+    std::vector<util::point2f> selected;
+
+    std::vector<util::point2f> candidates (samples);
+    std::uniform_real_distribution<float> dist_w (0, area.w);
+    std::uniform_real_distribution<float> dist_h (0, area.h);
+    std::random_device rd;
+    std::default_random_engine gen;
+
+    selected.push_back ({
+        dist_w (gen),
+        dist_h (gen),
+    });
+
+    auto min_distance = [&selected] (auto q) {
+        float min_d = INFINITY;
+
+        for (auto s: selected)
+            if (auto s_d = util::distance2 (s, q); s_d < min_d)
+                min_d = s_d;
+
+        return min_d;
+    };
+
+    while (1) {
+        util::point2f p;
+        float d = -INFINITY;
+
+        for (int i = 0; i < samples; ++i) {
+            util::point2f candidate { dist_w (gen), dist_h (gen) };
+
+            if (auto p_d = min_distance (candidate); p_d > d) {
+                p = candidate;
+                d = p_d;
+            }
+        }
+
+        if (std::sqrt (d) < distance)
+            break;
+
+        selected.push_back (p);
+    }
+
+    return selected;
+}
diff --git a/geom/sample.hpp b/geom/sample.hpp
index bf4cc88a..c87e7a11 100644
--- a/geom/sample.hpp
+++ b/geom/sample.hpp
@@ -11,14 +11,15 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *
- * Copyright 2015-2017 Danny Robson <danny@nerdcruft.net>
+ * Copyright 2015-2018 Danny Robson <danny@nerdcruft.net>
  */
 
 #ifndef __UTIL_GEOM_SAMPLE_HPP
 #define __UTIL_GEOM_SAMPLE_HPP
 
 #include "../coord/fwd.hpp"
-#include "./ops.hpp"
+#include "../extent.hpp"
+#include "ops.hpp"
 
 #include <cstddef>
 
@@ -72,6 +73,10 @@ namespace util::geom {
     {
         return sampler<S,T,K,G>::fn (k, g);
     }
+
+
+    std::vector<util::point2f>
+    poisson_sample (util::extent2i, float distance, int samples);
 }
 
 #endif