From 1e7a924874050674a103f6927f4a3c5ef6459222 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Fri, 13 Jun 2025 21:53:32 +0100
Subject: Create a list of snap points for the existing network

These form key positions in the world to ease neat creation.
---
 game/network/network.h | 14 ++++++++++++++
 game/network/rail.cpp  | 16 ++++++++++++++++
 game/network/rail.h    |  1 +
 test/test-network.cpp  |  6 ++++++
 ui/editNetwork.cpp     | 15 ++++++++++-----
 ui/editNetwork.h       |  1 +
 6 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/game/network/network.h b/game/network/network.h
index d3370b3..7bfd2ce 100644
--- a/game/network/network.h
+++ b/game/network/network.h
@@ -35,6 +35,19 @@ struct CreationDefinition {
 	CreationDefinitionEnd toEnd;
 };
 
+struct SnapPoint : CreationDefinitionEnd {
+	template<typename... CDE>
+		requires std::is_constructible_v<CreationDefinitionEnd, CDE...>
+	explicit SnapPoint(GlobalPosition3D snapPosition, CDE &&... cde) :
+		CreationDefinitionEnd {std::forward<CDE>(cde)...}, snapPosition(snapPosition)
+	{
+	}
+
+	GlobalPosition3D snapPosition;
+};
+
+using SnapPoints = std::vector<SnapPoint>;
+
 class Network {
 public:
 	using LinkEnd = std::pair<Link::Ptr, unsigned char>;
@@ -55,6 +68,7 @@ public:
 	[[nodiscard]] static Link::Nexts routeFromTo(const Link::End &, const Node::Ptr &);
 
 	[[nodiscard]] virtual float findNodeDirection(Node::AnyCPtr) const = 0;
+	[[nodiscard]] virtual SnapPoints getSnapPoints() const = 0;
 
 	[[nodiscard]] Link::Collection create(const GeoData *, const CreationDefinition &);
 	[[nodiscard]] Link::Collection createChain(const GeoData *, std::span<const GlobalPosition3D>);
diff --git a/game/network/rail.cpp b/game/network/rail.cpp
index 342a2ad..45d55d6 100644
--- a/game/network/rail.cpp
+++ b/game/network/rail.cpp
@@ -137,3 +137,19 @@ RailLinks::getBaseWidth() const
 	static constexpr auto BASE_WIDTH = 5'700;
 	return BASE_WIDTH;
 }
+
+SnapPoints
+RailLinks::getSnapPoints() const
+{
+	static constexpr auto EXTENSION_SNAP_DIST = 1'200.F;
+	SnapPoints out;
+	for (const auto & link : links) {
+		for (const auto & end : link->ends) {
+			// Link end node; directionless, suitable crossings
+			out.emplace_back(end.node->pos, end.node->pos, std::nullopt);
+			// Link end; with direction, suitable for continuing/joining
+			out.emplace_back(end.node->pos - ((sincos(end.dir) * EXTENSION_SNAP_DIST) || 0.F), end.node->pos, end.dir);
+		}
+	}
+	return out;
+}
diff --git a/game/network/rail.h b/game/network/rail.h
index 15b9ae4..48b1410 100644
--- a/game/network/rail.h
+++ b/game/network/rail.h
@@ -78,6 +78,7 @@ public:
 
 	[[nodiscard]] const Surface * getBaseSurface() const override;
 	[[nodiscard]] RelativeDistance getBaseWidth() const override;
+	[[nodiscard]] SnapPoints getSnapPoints() const override;
 
 private:
 	void tick(TickDuration elapsed) override;
diff --git a/test/test-network.cpp b/test/test-network.cpp
index 9a9ceb3..c3617b2 100644
--- a/test/test-network.cpp
+++ b/test/test-network.cpp
@@ -97,6 +97,12 @@ namespace {
 		{
 			return 5'700;
 		}
+
+		SnapPoints
+		getSnapPoints() const override
+		{
+			return {};
+		}
 	};
 
 	struct TestNetwork : public EmptyNetwork {
diff --git a/ui/editNetwork.cpp b/ui/editNetwork.cpp
index 98a60d3..20ec877 100644
--- a/ui/editNetwork.cpp
+++ b/ui/editNetwork.cpp
@@ -5,7 +5,7 @@
 #include <gfx/gl/sceneShader.h>
 #include <gfx/models/texture.h>
 
-EditNetwork::EditNetwork(Network * n) : network {n} { }
+EditNetwork::EditNetwork(Network * n) : network {n}, snapPoints {network->getSnapPoints()} { }
 
 bool
 EditNetwork::click(const SDL_MouseButtonEvent & event, const Ray<GlobalPosition3D> & ray)
@@ -34,6 +34,7 @@ EditNetwork::click(const SDL_MouseButtonEvent & event, const Ray<GlobalPosition3
 						currentStart.reset();
 					}
 					candidates.clear();
+					snapPoints = network->getSnapPoints();
 				}
 			}
 			return true;
@@ -63,16 +64,20 @@ EditNetwork::handleInput(const SDL_Event &)
 void
 EditNetwork::render(const SceneShader &, const Frustum &) const
 {
+	// TODO render snapPoints
 }
 
 std::optional<CreationDefinitionEnd>
 EditNetwork::resolveRay(const Ray<GlobalPosition3D> & ray) const
 {
 	if (const auto position = gameState->terrain->intersectRay(ray)) {
-		const auto node = network->intersectRayNodes(ray);
-		if (node) {
-			const auto direction = network->findNodeDirection(node);
-			return CreationDefinitionEnd {.position = node->pos, .direction = direction};
+		if (const auto closestSnapPoint = std::ranges::min_element(snapPoints, {},
+					[position](auto && snapPoint) {
+						return distance(position->first, snapPoint.snapPosition);
+					});
+				closestSnapPoint != snapPoints.end()
+				&& distance(position->first, closestSnapPoint->snapPosition) < 1'200.F) {
+			return *closestSnapPoint;
 		}
 		return CreationDefinitionEnd {.position = position->first, .direction = std::nullopt};
 	}
diff --git a/ui/editNetwork.h b/ui/editNetwork.h
index e155105..8011c1e 100644
--- a/ui/editNetwork.h
+++ b/ui/editNetwork.h
@@ -23,6 +23,7 @@ private:
 
 	Network * network;
 	bool continuousMode {false};
+	SnapPoints snapPoints;
 	std::optional<CreationDefinitionEnd> currentStart;
 	Link::Collection candidates;
 };
-- 
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