feat(editor): connections of tracks laid whole from the switch tool: a crossover with a straight insert or an aligning curve between switches of different angles or tracks that aren't parallel, a double crossover meeting on either track, a scissors crossover with the crossing of its inserts, and a switch ladder onto the parallel tracks of a fan or onto new ones at given spacings; press on a straight and drag onto the other track, Shift+wheel the kind, Ctrl+wheel the R of the aligning curve, Alt+wheel where a double crossover meets; the ghost shows the whole set with the spacing, the inserts and the distance of the mathematical points; switches get their drives and a //$r connection record; the crossover drawn from a diverging end uses the same solver; self-test connection

editor/editorConnections.hpp

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+/*
+This Source Code Form is subject to the
+terms of the Mozilla Public License, v.
+2.0. If a copy of the MPL was not
+distributed with this file, You can
+obtain one at
+http://mozilla.org/MPL/2.0/.
+*/
+
+#pragma once
+
+#include <array>
+#include <string>
+#include <vector>
+
+#include "editor/editorTrack.hpp"
+
+// connections of the straight tracks of a station made of switches: a crossover of two switches joined by a straight insert or
+// by an aligning curve between straight inserts, a double crossover of two crossovers one after the other, a scissors crossover
+// of two crossovers around one centre with a crossing between their inserts, a ladder of switches leading onto a fan of tracks
+namespace connection
+{
+
+enum class kind
+{
+	crossover,
+	double_crossover,
+	scissors,
+	ladder
+};
+int constexpr kind_count{4};
+char const *word(kind const Kind);
+bool parse(std::string const &Word, kind &Kind);
+
+struct line
+{
+	glm::dvec3 start{0.0};
+	glm::dvec2 direction{0.0, 1.0};
+	double grade{0.0};
+	double length{0.0};
+	glm::dvec3 point(double const Along) const;
+	double along(glm::dvec3 const &Point) const;
+	// to the left of the direction
+	double lateral(glm::dvec3 const &Point) const;
+};
+line of(editor_track::straight const &Straight);
+
+struct placed
+{
+	int line{0}; // 0 the starting track, 1 the other one, or the tracks of a fan in their order from 1, -1 the ladder track
+	double along{0.0}; // of the start of the switch along its line
+	int forward{1};
+	int side{1};
+	bool second{false}; // made of the template of the other tracks
+	std::vector<segment_data> paths;
+};
+
+// the switch on a track facing the end of a diverging track and the straight insert joining the two
+struct facing
+{
+	bool valid{false};
+	placed partner;
+	segment_data insert;
+	double length{0.0};
+	std::string error;
+};
+facing face(glm::dvec3 const &End, glm::dvec2 const &Heading, line const &To, int const Index, editor_track::switch_template const &Shape);
+
+struct request
+{
+	kind type{kind::crossover};
+	line from; // the track the connection starts on
+	std::vector<line> to; // the other track; for a ladder the tracks of the fan, the nearest first, or none
+	double along{0.0}; // of the start of the first switch on the starting track
+	int forward{1};
+	int side{0}; // of a ladder with no tracks of the fan to lead onto
+	double target{0.0}; // where the switch on the other track starts along it when no straight insert fixes the place
+	editor_track::switch_template first;
+	editor_track::switch_template second; // on the other tracks and along the ladder
+	double radius{0.0}; // of the aligning curves and of the end of a ladder, 0: of the sharper switch
+	double insert{6.0}; // the shortest straight between curves turning the opposite ways
+	double gap{6.0}; // of a double crossover: between the starts of the switches meeting on one track
+	bool together{false}; // of a double crossover: the switches meet on the starting track, not on the other one
+	std::vector<double> spacings; // of a ladder with no tracks of the fan: from the starting track to the first one and on
+	double stub{25.0}; // of a ladder: length of the new tracks of the fan
+};
+
+struct result
+{
+	bool valid{false};
+	std::string error;
+	std::string warning;
+	std::vector<placed> switches;
+	std::vector<segment_data> inserts;
+	std::vector<double> straights; // lengths of the straight inserts between the switches
+	double spacing{0.0}; // of the tracks at the start of the first switch
+	double points{0.0}; // between the mathematical points of the switches of the first crossover
+	double radius{0.0}; // of the aligning curve, 0 when a straight insert joins the switches
+	std::vector<double> fan; // offsets of the tracks of a ladder from the starting track
+	bool crossing{false}; // of a scissors crossover, at the meeting of its two inserts
+	std::array<glm::dvec3, 4> ends{}; // of the two inserts crossing: along the first one, then along the second one
+	glm::dvec3 centre{0.0};
+	double angle{0.0};
+};
+result plan(request const &Request);
+
+} // namespace connection