From 966c506f3cd58372c94f134a556ca2d406c863da Mon Sep 17 00:00:00 2001
From: Andrew Bell <andrew.bell.ia@gmail.com>
Date: Fri, 10 May 2019 14:17:55 -0400
Subject: [PATCH] Fix WKT generation for polygons with islands.

---
 filters/private/hexer/HexGrid.cpp | 20 ++++------
 filters/private/hexer/Path.cpp    | 65 ++++++++++++++++++++++---------
 filters/private/hexer/Path.hpp    | 13 +++++--
 3 files changed, 64 insertions(+), 34 deletions(-)

diff --git a/filters/private/hexer/HexGrid.cpp b/filters/private/hexer/HexGrid.cpp
index 6892ef703a..8a54c8ff82 100644
--- a/filters/private/hexer/HexGrid.cpp
+++ b/filters/private/hexer/HexGrid.cpp
@@ -368,27 +368,23 @@ void HexGrid::cleanPossibleRoot(Segment s, Path *p)
     }
 }
 
-void HexGrid::toWKT(std::ostream& output) const
+void HexGrid::toWKT(std::ostream& out) const
 {
-    auto outputPath = [this,&output](size_t pathNum)
+    auto writePath = [this, &out](size_t pathNum)
     {
-        Path *p = rootPaths()[pathNum];
-
-        output << "(";
-        p->toWKT(output);
-        output << ")";
+       rootPaths()[pathNum]->toWKT(out);
     };
 
-    output << "MULTIPOLYGON (";
+    out << "MULTIPOLYGON (";
 
     if (rootPaths().size())
-        outputPath(0);
+        writePath(0);
     for (size_t pi = 1; pi < rootPaths().size(); ++pi)
     {
-        output << ",";
-        outputPath(pi);
+        out << ",";
+        writePath(pi);
     }
-    output << ")";
+    out << ")";
 }
 
 size_t HexGrid::densePointCount() const
diff --git a/filters/private/hexer/Path.cpp b/filters/private/hexer/Path.cpp
index d102c4c4b3..a16845ef62 100644
--- a/filters/private/hexer/Path.cpp
+++ b/filters/private/hexer/Path.cpp
@@ -66,34 +66,63 @@ vector<Point> Path::points() const
     return points;
 }
 
-void Path::toWKT( std::ostream& output) const
+void Path::writeRing(std::ostream& out) const
 {
-    vector<Point> pts = points();
-
-    auto outputPoint = [&output](Point& p)
+    auto outputPoint = [&out](const Point& p)
     {
-        output << p.m_x << " " << p.m_y;
+        out << p.m_x << " " << p.m_y;
     };
 
-    output << "(";
+    const vector<Point>& pts = points();
+    assert(pts.size() > 2);
+    out << "(";
+    outputPoint(pts.front());
+    for (auto it = pts.begin() + 1; it != pts.end(); ++it)
+    {
+        out << ", ";
+        outputPoint(*it);
+    }
+    out << ")";
+}
 
-    auto pi = pts.begin();
-    if (pi != pts.end())
-        outputPoint(*pi++);
-    for (; pi != pts.end(); ++pi)
+// WKT (or GeoJSON) doesn't allow nesting of polygons.  You can just have
+// polygons and holes.  Islands within the holes need to be described as
+// separate polygons.  To that end, we grather the islands from all holes
+// and return them to be processed as separate polygons.
+PathPtrList Path::writePolygon(std::ostream& out) const
+{
+    PathPtrList islands;
+
+    out << "(";
+    writeRing(out);
+    const PathPtrList& paths = subPaths();
+    for (auto& p : paths)
     {
-        output << ", ";
-        outputPoint(*pi);
+        out << ", ";
+        p->writeRing(out);
+        const PathPtrList& subs(p->subPaths());
+        islands.insert(islands.end(), subs.begin(), subs.end());
     }
+    out << ")";
+    return islands;
+}
 
-    output << ")";
 
-    vector<Path *> paths = subPaths();
-    for (size_t pi = 0; pi != paths.size(); ++pi)
+void Path::toWKT(std::ostream& out) const
+{
+    PathPtrList islands = writePolygon(out);
+
+    // See the note on writePolygon()
+    while (islands.size())
     {
-        Path* p = paths[pi];
-        output <<",";
-        p->toWKT(output);
+        PathPtrList paths;
+        paths.swap(islands);
+        for (Path *p : paths)
+        {
+            out << ", ";
+            PathPtrList subIslands = p->writePolygon(out);
+            islands.insert(islands.end(), subIslands.begin(), subIslands.end());
+        }
     }
 }
 
diff --git a/filters/private/hexer/Path.hpp b/filters/private/hexer/Path.hpp
index 9d3a448fa9..8b34c548ae 100644
--- a/filters/private/hexer/Path.hpp
+++ b/filters/private/hexer/Path.hpp
@@ -49,6 +49,8 @@ enum Orientation
 };
 
 class HexGrid;
+class Path;
+using PathPtrList = std::vector<Path *>;
 
 class Path
 {
@@ -59,8 +61,8 @@ class Path
 
     ~Path()
     {
-        for (std::vector<Path*>::size_type i = 0; i < m_children.size(); ++i)
-            delete m_children[i];
+        for (auto p : m_children)
+            delete p;
     }
 
     void push_back(const Segment& s)
@@ -85,7 +87,7 @@ class Path
     Orientation orientation() const
         { return m_orientation; }
     std::vector<Point> points() const;
-    std::vector<Path *> subPaths() const
+    PathPtrList subPaths() const
         { return m_children; }
     void toWKT( std::ostream& output) const;
 
@@ -95,12 +97,15 @@ class Path
     /// Parent path (NULL if root path)
     Path *m_parent;
     /// Children
-    std::vector<Path *> m_children;
+    PathPtrList m_children;
     /// Orientation of path AT EXTRACTION - segments are ALWAYS ordered
     /// clockwise.
     Orientation m_orientation;
     /// List of segments that make up the path.
     std::vector<Segment> m_segs;
+
+    void writeRing(std::ostream& out) const;
+    PathPtrList writePolygon(std::ostream& out) const;
 };
 
 } //namespace hexer