feat(editor): bends clicked close along a curve make one compound curve, not curves with short straights between them: a row of bends turning the same way, the straights between their curves shorter than as many metres as km/h of the speed (30 m at least), is taken for points of a curve seen on the photo, one curve fitted through them between the straights before and after it, with as many radii meeting with no transitions between them as keep it within 0.3 m of the points, up to eight, and taken where it keeps within 1 m; a row which doesn't is cut in parts, two bends alone joined into one curve along the line their curves laid. A curve traced is two curves turning the same way only with a straight between them as long as that and keeping much closer to the points than one compound curve; a fit running off to the largest radius gives two transition curves meeting. The transitions fitted turn no more than the curve; arcs and spirals are found many times quicker, the curve of a compound fit made straight away, a transition integrated in 64 steps at most. The fits wait on the thread of the laying in a queue of their own, the one asked for last fitted first

editor/editorAlignment.hpp

@@ -10,6 +10,7 @@ http:
 #pragma once
 
 #include <condition_variable>
+#include <functional>
 #include <mutex>
 #include <optional>
 #include <string>
@@ -338,26 +339,32 @@ struct corner_radii
 	double low{3000.0};
 	double high{6000.0};
 };
-// the vertices marked are given the curves of the bends of straights clicked on the photo, as large as fit between the neighbouring
-// ones, these sharing the straights between them; the vertices stay where they are, a curve below the norms is left with its warnings
-result ease_corners(design &Design, std::vector<char> const &Corners, corner_radii const &Radii);
-
 // a stretch of the line traced on the photo: the points clicked along the middle of the track, from the straight Base starts on to
 // the one it ends on, both fixed by the points clicked on them
 struct trace_stretch
 {
 	bool valid{false};
 	// the curves of the stretch with their places: one, of up to three radii, or two with a straight between them where the points
-	// follow those better; none where the stretch is straight
+	// follow those much better; none where the stretch is straight
 	std::vector<vertex> vertices;
 	std::vector<double> offsets; // of the points from the line laid, positive to the left
 	double rms{0.0};
 	double worst{0.0};
 };
 trace_stretch fit_trace_stretch(design const &Base, std::vector<glm::dvec2> const &Points, int const Radii, bool const Straights);
+// the fit of a stretch traced, with up to three radii and no straight in it; none while it's being fitted elsewhere
+using stretch_fit = std::function<std::optional<trace_stretch>(design const &, std::vector<glm::dvec2> const &)>;
 
-// the stretches traced fitted on a thread of their own while the cursor moves: fitting one takes tens of milliseconds. The latest one
-// asked for is fitted, the ones asked for meanwhile are left out
+// the vertices marked 1 are given the curves of the bends of straights clicked on the photo, as large as fit between the neighbouring
+// ones, these sharing the straights between them; the vertices stay where they are, a curve below the norms is left with its
+// warnings. A row of bends turning the same way, clicked so close that the straights between their curves would be shorter than
+// the shortest element, is taken for points along a curve: one curve, compound where it has to, is fitted through them, or one for
+// each part of the row where the whole doesn't keep to them; such a vertex is marked 0 then. Fit fits it, by fit_trace_stretch
+// where none is given
+result ease_corners(design &Design, std::vector<char> &Corners, corner_radii const &Radii, stretch_fit const &Fit = {});
+
+// the stretches traced fitted on a thread of their own while the cursor moves: fitting one takes tens of milliseconds. The one asked
+// for last is fitted first, the oldest of too many waiting left out, the fits of the last ones kept
 class stretch_fitter
 {
   public:
@@ -381,9 +388,9 @@ class stretch_fitter
 
 	mutable std::mutex m_mutex;
 	std::condition_variable m_wake;
-	std::optional<request> m_asked;
+	std::vector<request> m_asked;
 	std::optional<request> m_fitting;
-	std::optional<std::pair<std::vector<double>, trace_stretch>> m_result;
+	std::vector<std::pair<std::vector<double>, trace_stretch>> m_results; // the last done first
 	bool m_stop{false};
 	std::thread m_thread;
 };