From 838e5f77478e5648769439e191e3ff0a8e6405ab Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Mon, 22 Feb 2021 20:12:59 +0000
Subject: Add meandering support

Add rail links between existing nodes and arbitrary points
---
 utility/maths.cpp | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

(limited to 'utility/maths.cpp')

diff --git a/utility/maths.cpp b/utility/maths.cpp
index 0bd3eac..74a3085 100644
--- a/utility/maths.cpp
+++ b/utility/maths.cpp
@@ -3,6 +3,8 @@
 #include <glm/glm.hpp>
 #include <glm/gtx/rotate_vector.hpp>
 #include <glm/gtx/transform.hpp>
+#include <initializer_list>
+#include <stdexcept>
 
 glm::mat4
 flat_orientation(const glm::vec3 & diff)
@@ -57,3 +59,29 @@ Arc::Arc(const glm::vec3 & centre3, const glm::vec3 & e0p, const glm::vec3 & e1p
 	}())
 {
 }
+
+std::pair<glm::vec2, bool>
+find_arc_centre(glm::vec2 as, float entrys, glm::vec2 bs, float entrye)
+{
+	if (as == bs) {
+		return {as, false};
+	}
+	for (const auto lr : {1.F, -1.F}) { // left or right turn (maybe possible with removal of positve check below)
+		const auto perps = entrys + (half_pi * lr);
+		const auto perpe = entrye - (half_pi * lr);
+		const glm::vec2 ad {std::sin(perps), std::cos(perps)};
+		const glm::vec2 bd {std::sin(perpe), std::cos(perpe)};
+
+		const auto dx = bs.x - as.x;
+		const auto dy = bs.y - as.y;
+		const auto det = bd.x * ad.y - bd.y * ad.x;
+		if (det != 0) { // near parallel line will yield noisy results
+			const auto u = (dy * bd.x - dx * bd.y) / det;
+			const auto v = (dy * ad.x - dx * ad.y) / det;
+			if (u >= 0 && v >= 0) {
+				return {as + ad * u, lr < 0};
+			}
+		}
+	}
+	throw std::runtime_error("no intersection");
+}
-- 
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