JAL-3032 adds Java 8 functionality (2/2)

[jalview.git] / src2 / fr / orsay / lri / varna / models / geom / ComputeArcCenter.java

diff --git a/src2/fr/orsay/lri/varna/models/geom/ComputeArcCenter.java b/src2/fr/orsay/lri/varna/models/geom/ComputeArcCenter.java
new file mode 100644 (file)
index 0000000..0aa8ebf
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+++ b/src2/fr/orsay/lri/varna/models/geom/ComputeArcCenter.java
@@ -0,0 +1,54 @@
+/**
+ * File written by Raphael Champeimont
+ * UMR 7238 Genomique des Microorganismes
+ */
+package fr.orsay.lri.varna.models.geom;
+
+public class ComputeArcCenter {
+       
+       /**
+        * Given an arc length (l) and segment length (delta) of the arc,
+        * find where to put the center, returned as a position of the perpendicular
+        * bisector of the segment. The positive side is the one where the arc is drawn.
+        * It works using Newton's method.
+        */
+       public static double computeArcCenter(double delta, double l) {
+               double x_n = 0;
+               double x_n_plus_1, f_x_n, f_x_n_plus_1;
+               f_x_n = f(x_n,delta);
+               while (true) {
+                       x_n_plus_1 = x_n - (f_x_n - l)/fprime(x_n,delta);
+                       f_x_n_plus_1 = f(x_n_plus_1,delta);
+                       // We want a precision of 0.1 on arc length
+                       if (x_n_plus_1 == Double.NEGATIVE_INFINITY || Math.abs(f_x_n_plus_1 - f_x_n) < 0.1) {
+                               //System.out.println("computeArcCenter: steps = " + steps + "    result = " + x_n_plus_1);
+                               return x_n_plus_1;
+                       }
+                       x_n = x_n_plus_1;
+                       f_x_n = f_x_n_plus_1;
+               }
+       }
+       
+       private static double f(double c, double delta) {
+               if (c < 0) {
+                       return 2*Math.atan(delta/(-2*c)) * Math.sqrt(delta*delta/4 + c*c);
+               } else if (c != 0) { // c > 0
+                       return (2*Math.PI - 2*Math.atan(delta/(2*c))) * Math.sqrt(delta*delta/4 + c*c);
+               } else { // c == 0
+                       return Math.PI * Math.sqrt(delta*delta/4 + c*c);
+               }
+       }
+       
+       /**
+        * d/dc f(c,delta)
+        */
+       private static double fprime(double c, double delta) {
+               if (c < 0) {
+                       return delta/(c*c + delta/4)*Math.sqrt(delta*delta/4 + c*c) + 2*Math.atan(delta/(-2*c))*c/Math.sqrt(delta*delta/4 + c*c);
+               } else if (c != 0) { // c > 0
+                       return delta/(c*c + delta/4)*Math.sqrt(delta*delta/4 + c*c) + (2*Math.PI - 2*Math.atan(delta/(-2*c)))*c/Math.sqrt(delta*delta/4 + c*c);
+               } else { // c == 0
+                       return 2;
+               }
+       }
+}
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