From 37b135e59ba22cf9ace1141b9dd21d0819fe3d1d Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Tue, 25 Oct 2022 18:49:19 +0100
Subject: Implement extending a network into open space

---
 game/network/network.cpp    | 16 ++++++++++++++++
 game/network/network.h      |  4 ++++
 game/network/network.impl.h | 10 ++++++----
 game/network/rail.h         |  2 ++
 test/test-network.cpp       |  4 +++-
 5 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/game/network/network.cpp b/game/network/network.cpp
index ad501b5..7724c20 100644
--- a/game/network/network.cpp
+++ b/game/network/network.cpp
@@ -93,3 +93,19 @@ Network::routeFromTo(const Link::End & end, const Node::Ptr & dest) const
 {
 	return RouteWalker().findRouteTo(end, dest);
 }
+
+GenCurveDef
+Network::genCurveDef(const glm::vec3 & start, const glm::vec3 & end, float startDir)
+{
+	const auto diff {end - start};
+	const auto vy {vector_yaw(diff)};
+	const auto dir = pi + startDir;
+	const auto flatStart {!start}, flatEnd {!end};
+	const auto n2ed {(vy * 2) - dir - pi};
+	const auto centre {find_arc_centre(flatStart, dir, flatEnd, n2ed)};
+
+	if (centre.second) { // right hand arc
+		return {end, start, centre.first};
+	}
+	return {start, end, centre.first};
+}
diff --git a/game/network/network.h b/game/network/network.h
index f1ac23f..f37f335 100644
--- a/game/network/network.h
+++ b/game/network/network.h
@@ -15,6 +15,9 @@ class Texture;
 class Shader;
 class Ray;
 
+template<size_t... n> using GenDef = std::tuple<glm::vec<n, float>...>;
+using GenCurveDef = GenDef<3, 3, 2>;
+
 class Network {
 public:
 	using LinkEnd = std::pair<Link::Ptr, unsigned char>;
@@ -44,6 +47,7 @@ public:
 
 protected:
 	static void joinLinks(const Link::Ptr & l, const Link::Ptr & ol);
+	static GenCurveDef genCurveDef(const glm::vec3 & start, const glm::vec3 & end, float startDir);
 
 	using Nodes = std::set<Node::Ptr, PtrMemberSorter<Node::Ptr, &Node::pos>>;
 	Nodes nodes;
diff --git a/game/network/network.impl.h b/game/network/network.impl.h
index cee8155..859d1ac 100644
--- a/game/network/network.impl.h
+++ b/game/network/network.impl.h
@@ -68,9 +68,10 @@ NetworkOf<T>::candidateJoins(glm::vec3 n1, glm::vec3 n2)
 
 template<typename T>
 Link::CCollection
-NetworkOf<T>::candidateExtend(glm::vec3 n1, glm::vec3 n2)
+NetworkOf<T>::candidateExtend(glm::vec3 start, glm::vec3 end)
 {
-	return {candidateLink<typename T::StraightLink>(n1, n2)};
+	const auto [cstart, cend, centre] = genCurveDef(start, end, findNodeDirection(candidateNodeAt(start).first));
+	return {candidateLink<typename T::CurveLink>(cstart, cend, centre)};
 }
 
 template<typename T>
@@ -89,7 +90,8 @@ NetworkOf<T>::addJoins(glm::vec3 n1, glm::vec3 n2)
 
 template<typename T>
 Link::CCollection
-NetworkOf<T>::addExtend(glm::vec3 n1, glm::vec3 n2)
+NetworkOf<T>::addExtend(glm::vec3 start, glm::vec3 end)
 {
-	return {addLink<typename T::StraightLink>(n1, n2)};
+	const auto [cstart, cend, centre] = genCurveDef(start, end, findNodeDirection(nodeAt(start)));
+	return {addLink<typename T::CurveLink>(cstart, cend, centre)};
 }
diff --git a/game/network/rail.h b/game/network/rail.h
index b1a036e..6850463 100644
--- a/game/network/rail.h
+++ b/game/network/rail.h
@@ -17,12 +17,14 @@ struct Arc;
 
 // A piece of rail track
 class RailLinkStraight;
+class RailLinkCurve;
 class RailLink : public virtual Link, public Renderable {
 public:
 	RailLink() = default;
 	inline ~RailLink() override = 0;
 
 	using StraightLink = RailLinkStraight;
+	using CurveLink = RailLinkCurve;
 
 	void render(const Shader &) const override;
 	NO_COPY(RailLink);
diff --git a/test/test-network.cpp b/test/test-network.cpp
index fb4c87c..dc2b52f 100644
--- a/test/test-network.cpp
+++ b/test/test-network.cpp
@@ -19,9 +19,11 @@
 #include <vector>
 
 struct TestLink : public LinkStraight {
-	TestLink(Node::Ptr a, Node::Ptr b) : TestLink {a, b, glm::distance(a->pos, b->pos)} { }
+	TestLink(Node::Ptr a, Node::Ptr b) : TestLink {a, b, (a->pos - b->pos)} { }
+	TestLink(Node::Ptr a, Node::Ptr b, glm::vec2 l) : Link {{std::move(a), 0}, {std::move(b), pi}, glm::length(l)} { }
 	TestLink(Node::Ptr a, Node::Ptr b, float l) : Link {{std::move(a), 0}, {std::move(b), pi}, l} { }
 	using StraightLink = TestLink;
+	using CurveLink = TestLink;
 };
 
 constexpr glm::vec3 p000 {0, 0, 0}, p100 {1, 0, 0}, p200 {2, 0, 0}, p300 {3, 0, 0};
-- 
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