From 0fe44770974c49687272a5f166bd0207761e6f5c Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Fri, 16 Sep 2022 19:39:42 +0300
Subject: [PATCH] Add cg::edge_mesh(dcel) and cg::triangle_mesh(dcel)

---
 libs/cg/include/psemek/cg/dcel.hpp | 54 ++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/libs/cg/include/psemek/cg/dcel.hpp b/libs/cg/include/psemek/cg/dcel.hpp
index d987a78d..ab1c7a96 100644
--- a/libs/cg/include/psemek/cg/dcel.hpp
+++ b/libs/cg/include/psemek/cg/dcel.hpp
@@ -2,6 +2,7 @@
 
 #include <psemek/util/empty.hpp>
 #include <psemek/util/ebo.hpp>
+#include <psemek/geom/simplex.hpp>
 
 #include <cstddef>
 #include <vector>
@@ -599,4 +600,57 @@ namespace psemek::cg
 		return result;
 	}
 
+	template <typename Point, typename Edge, typename Face, typename Index, typename OutputIterator>
+	OutputIterator edge_mesh(dcel<Point, Edge, Face, Index> const & dcel, OutputIterator out)
+	{
+		std::vector<bool> visited(dcel.edges.size(), false);
+		for (Index e = 0; e < dcel.edges.size(); ++e)
+		{
+			if (visited[e]) continue;
+
+			auto twin = dcel.edges[e].twin;
+
+			visited[e] = true;
+			visited[twin] = true;
+
+			auto h = dcel.edge(e);
+
+			*out++ = geom::segment<Index>{h.origin().index(), h.twin().origin().index()};
+		}
+		return out;
+	}
+
+	template <typename Point, typename Edge, typename Face, typename Index>
+	auto edge_mesh(dcel<Point, Edge, Face, Index> const & dcel)
+	{
+		std::vector<geom::segment<Index>> result;
+		edge_mesh(dcel, std::back_inserter(result));
+		return result;
+	}
+
+	template <typename Point, typename Edge, typename Face, typename Index, typename OutputIterator>
+	OutputIterator triangle_mesh(dcel<Point, Edge, Face, Index> const & dcel, OutputIterator out)
+	{
+		for (Index f = 1; f < dcel.faces.size(); ++f)
+		{
+			auto h = dcel.face(f).edge();
+
+			geom::triangle<Index> t;
+			t[0] = h.origin().index(); h = h.next();
+			t[1] = h.origin().index(); h = h.next();
+			t[2] = h.origin().index();
+
+			*out++ = t;
+		}
+		return out;
+	}
+
+	template <typename Point, typename Edge, typename Face, typename Index>
+	auto triangle_mesh(dcel<Point, Edge, Face, Index> const & dcel)
+	{
+		std::vector<geom::triangle<Index>> result;
+		triangle_mesh(dcel, std::back_inserter(result));
+		return result;
+	}
+
 }