X-Git-Url: http://source.jalview.org/gitweb/?p=jalview.git;a=blobdiff_plain;f=src2%2Ffr%2Forsay%2Flri%2Fvarna%2Fmodels%2Fgeom%2FComputeArcCenter.java;fp=src2%2Ffr%2Forsay%2Flri%2Fvarna%2Fmodels%2Fgeom%2FComputeArcCenter.java;h=0aa8ebf724827ce9061524cc64dc370a26644aa1;hp=0000000000000000000000000000000000000000;hb=665d2c2f4c1310e6985b93b7c2c8a8eec2fa9086;hpb=0e684f72690bd6532272a39ab6c188a27559fd09

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
index 0000000..0aa8ebf
--- /dev/null
+++ 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;
+		}
+	}
+}
\ No newline at end of file