From b0918628b40c22923e599b02a6987ac47ab5afcf Mon Sep 17 00:00:00 2001
From: maj00r <maj00r@host>
Date: Tue, 27 Oct 2026 19:41:50 +0100
Subject: [PATCH] fix(editor): a curve traced from the end of the diverging
 track of a switch with one point clicked goes on with the curve of the switch
 as far as abreast of the point, seen from its centre, and ends on it there,
 instead of turning into a straight where the straight to the point left it:
 the curve is held to where it was clicked, a point inside it as well.
 Selftest: one point after P4 of a Rz 60E1-300-1:9 laid R 300 m on to 238.36
 13.31 for a point at 240 8, to 243.31 14.88 for one at 240 25, the curvature
 at P4 going on within 0.5 %

---
 application/editormodelay.cpp | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/application/editormodelay.cpp b/application/editormodelay.cpp
index 934bbce6..25ea4052 100644
--- a/application/editormodelay.cpp
+++ b/application/editormodelay.cpp
@@ -1148,8 +1148,8 @@ bool editor_mode::lay_line(std::vector<glm::dvec3> const &Points, std::vector<la
 		while (last < inner && mode_of(last) == lay_mode::curve)
 			++last;
 		auto const reaching{last == inner && joined};
-		// one point of a curve right after the end of the diverging track of a switch: the curve of the switch goes on towards it, then a
-		// straight from where it heads for the point; the curve fitted to the points once more of them are clicked
+		// one point of a curve right after the end of the diverging track of a switch: the curve of the switch goes on as far as abreast of
+		// the point, seen from its centre, the line ending on it there; the curve fitted to the points once more of them are clicked
 		if (i == 1 && last == 2 && false == reaching && along.has_value() && design.start_curved && design.start_radius > 0.0 && tool.start.track != nullptr && tool.start.track->eType == tt_Switch)
 		{
 			auto const radius{design.start_radius};
@@ -1157,25 +1157,21 @@ bool editor_mode::lay_line(std::vector<glm::dvec3> const &Points, std::vector<la
 			auto const from{plan_of(anchor)};
 			glm::dvec2 const inward{-along->y * side, along->x * side};
 			auto const centre{from + inward * radius};
-			auto const point{plan_of(Points[1])};
-			auto const outward{point - centre};
-			auto const distance{glm::length(outward)};
-			if (distance > radius + 0.5)
+			auto const outward{plan_of(Points[1]) - centre};
+			if (glm::length(outward) > 0.5)
 			{
-				// where the straight to the point touches the circle, and how far round the curve turns to there
-				auto const heading{std::atan2(outward.y, outward.x) - side * std::acos(radius / distance)};
-				glm::dvec2 const touch{centre + glm::dvec2{std::cos(heading), std::sin(heading)} * radius};
-				auto turned{std::fmod(side * (heading - std::atan2(from.y - centre.y, from.x - centre.x)), 2.0 * glm::pi<double>())};
-				if (turned < 0.0)
-					turned += 2.0 * glm::pi<double>();
-				if (turned > 1e-3 && turned < glm::pi<double>())
+				// how far round the curve turns to there
+				auto sweep{std::fmod(side * (std::atan2(outward.y, outward.x) - std::atan2(from.y - centre.y, from.x - centre.x)), 2.0 * glm::pi<double>())};
+				if (sweep < 0.0)
+					sweep += 2.0 * glm::pi<double>();
+				if (sweep > 1e-3 && sweep < glm::pi<double>())
 				{
 					alignment::vertex curve;
 					curve.radius = radius;
 					curve.cant = design.start_cant;
-					bends.push_back({lifted(from + *along * (radius * std::tan(0.5 * turned)), anchor.y), curve, false});
-					anchor = Points[1];
-					along = glm::normalize(point - touch);
+					bends.push_back({lifted(from + *along * (radius * std::tan(0.5 * sweep)), anchor.y), curve, false});
+					anchor = lifted(centre + glm::normalize(outward) * radius, Points[1].y);
+					along = turned(*along, side * sweep);
 					i = last;
 					continue;
 				}