From 21203053a99c1bc6ce5d502131dc9d964d30d842 Mon Sep 17 00:00:00 2001
From: Jaron Kent-Dobias <jaron@kent-dobias.com>
Date: Sun, 23 Dec 2018 11:33:02 -0500
Subject: cleaned up graph a bit, redefined assert so that certain run errors
 in jc_voronoi can be caught

---
 lib/src/graph.cpp | 39 +++++++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 12 deletions(-)

(limited to 'lib')

diff --git a/lib/src/graph.cpp b/lib/src/graph.cpp
index 3d5647f..b9d4f03 100644
--- a/lib/src/graph.cpp
+++ b/lib/src/graph.cpp
@@ -6,8 +6,12 @@
 #define JCV_REAL_TYPE double
 #define JCV_ATAN2 atan2
 #define JCV_FLT_MAX 1.7976931348623157E+308
+#undef assert
+#define assert_error_report_helper(cond) "assertion failed: "
+#define assert(cond) {if(!(cond)) { std::cerr << assert_error_report_helper(cond) "\n"; throw assert_error_report_helper(cond); } }
 #include <jc_voronoi.h>
 
+// actual mod for floats
 double mod(double a, double b) {
   if (a >= 0) {
     return fmod(a, b);
@@ -95,26 +99,30 @@ class eulerException: public std::exception
 graph::graph(double Lx, double Ly, std::mt19937& rng, double relax, double step) {
   L = {Lx, Ly};
 
+  // randomly choose N to be floor(Lx * Ly / 2) or ceil(Lx * Ly / 2) with
+  // probability proportional to the distance from each
   std::uniform_real_distribution<double> d(0.0, 1.0);
   unsigned int N = round(Lx * Ly / 2 + d(rng) - 0.5);
 
   unsigned int nv = N;
-
   vertices.resize(nv);
 
   // the coordinates of the lattice, from which a delaunay triangulation
-  // and corresponding voronoi tessellation will be built
+  // and corresponding voronoi tessellation will be built. Everyone is in the
+  // rectangle (0, 0) (Lx, Ly)
   for (unsigned int i = 0; i < nv; i++) {
     vertices[i] = {{L.x * d(rng), L.y * d(rng)}};
   }
 
-  double max_difference = std::numeric_limits<double>::max();
+  // set up the voronoi objects
   jcv_diagram diagram;
   memset(&diagram, 0, sizeof(jcv_diagram));
+  jcv_rect bounds = {{-Lx, -Ly}, {2 * Lx, 2 * Ly}};
   std::vector<jcv_point> points(9 * nv);
 
   double rstep = sqrt(step);
 
+  double max_difference = std::numeric_limits<double>::max();
   while (max_difference > pow(relax, 2) * 2 * N) {
     double cur_diff = 0;
     // to make the resulting tessellation periodic, we tile eight (!) copies of
@@ -123,6 +131,7 @@ graph::graph(double Lx, double Ly, std::mt19937& rng, double relax, double step)
     // translate back)
     for (unsigned int i = 0; i < nv; i++) {
       const vertex& v = vertices[i];
+
       points[9 * i + 0] = {v.r.x + 0.0, v.r.y + 0.0};
       points[9 * i + 1] = {v.r.x + L.x, v.r.y + 0.0};
       points[9 * i + 2] = {v.r.x - L.x, v.r.y + 0.0};
@@ -134,27 +143,33 @@ graph::graph(double Lx, double Ly, std::mt19937& rng, double relax, double step)
       points[9 * i + 8] = {v.r.x - L.x, v.r.y - L.y};
     }
 
-    jcv_diagram_generate(9 * nv, points.data(), NULL, &diagram);
+    // run voronoi
+    jcv_diagram_generate(9 * nv, points.data(), &bounds, &diagram);
+
+    // relax the sites by moving the vertices towards their centroids
     const jcv_site* sites = jcv_diagram_get_sites(&diagram);
-    
     for (int i = 0; i < diagram.numsites; i++) {
       const jcv_site* site = &sites[i];
       unsigned int ind = site->index;
       if (ind % 9 == 0) {
         double Cx = 0.0;
         double Cy = 0.0;
-        unsigned int ne = 0;
+        double A = 0.0;
 
         const jcv_graphedge* e = site->edges;
         while (e) {
-          ne++;
-          Cx += e->pos[0].x;
-          Cy += e->pos[0].y;
+          double dA = e->pos[0].x * e->pos[1].y - e->pos[1].x * e->pos[0].y;
+
+          A += dA;
+          Cx += (e->pos[0].x + e->pos[1].x) * dA;
+          Cy += (e->pos[0].y + e->pos[1].y) * dA;
+
           e = e->next;
         }
 
-        Cx /= ne;
-        Cy /= ne;
+        A /= 2;
+        Cx /= 6 * A;
+        Cy /= 6 * A;
 
         double dx = Cx - vertices[ind / 9].r.x;
         double dy = Cy - vertices[ind / 9].r.y;
@@ -183,7 +198,7 @@ graph::graph(double Lx, double Ly, std::mt19937& rng, double relax, double step)
     points[9 * i + 7] = {v.r.x + L.x, v.r.y - L.y};
     points[9 * i + 8] = {v.r.x - L.x, v.r.y - L.y};
   }
-  jcv_diagram_generate(9 * nv, points.data(), NULL, &diagram);
+  jcv_diagram_generate(9 * nv, points.data(), &bounds, &diagram);
 
   const jcv_site* sites = jcv_diagram_get_sites(&diagram);
 
-- 
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