-/**
- * File written by Raphael Champeimont
- * UMR 7238 Genomique des Microorganismes
- */
-package fr.orsay.lri.varna.models.geom;
-
-import java.awt.geom.Line2D;
-import java.awt.geom.Point2D;
-
-/**
- * Like Line2D.Double.linesIntersect() of the standard library, but without the bug!
- * See this: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6457965
- * This result is incorrect with, for example:
- * System.out.println(Line2D.Double.linesIntersect(179.2690296114372, 1527.2309703885628, 150.9847583639753, 1498.946699141101, 94.4162158690515, 1442.378156646177, 66.1319446215896, 1414.0938853987152));
- * (real example observed on an RNA with no intersection at all)
- * This lines obviously don't intersect (both X and Y ranges are clearly disjoint!)
- * but linesIntersect() returns true.
- * Here we provide a bug-free function.
- */
-public class LinesIntersect {
- /**
- * Returns whether segment from (x1,y1) to (x2,y2)
- * intersect with segment from (x3,y3) to (x4,y4).
- */
- public static boolean linesIntersect(
- double x1,
- double y1,
- double x2,
- double y2,
- double x3,
- double y3,
- double x4,
- double y4) {
-
- double denom = (y4 - y3) * (x2 - x1) - (x4 - x3) * (y2 - y1);
- if (denom == 0.0) { // Lines are parallel.
- return false;
- }
- double ua = ((x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3)) / denom;
- double ub = ((x2 - x1) * (y1 - y3) - (y2 - y1) * (x1 - x3)) / denom;
- return (ua >= 0.0 && ua <= 1.0 && ub >= 0.0 && ub <= 1.0);
- }
-
- /**
- * Returns whether segment from p1 to p2 intersects segment from p3 to p4.
- */
- public static boolean linesIntersect(
- Point2D.Double p1,
- Point2D.Double p2,
- Point2D.Double p3,
- Point2D.Double p4) {
- return linesIntersect(p1.x, p1.y, p2.x, p2.y, p3.x, p3.y, p4.x, p4.y);
- }
-
- /**
- * Returns whether the two segment intersect.
- */
- public static boolean linesIntersect(Line2D.Double line1, Line2D.Double line2) {
- return linesIntersect(
- line1.x1, line1.y1, line1.x2, line1.y2,
- line2.x1, line2.y1, line2.x2, line2.y2);
- }
-
-
- private static void test(
- double x1,
- double y1,
- double x2,
- double y2,
- double x3,
- double y3,
- double x4,
- double y4,
- boolean expectedResult) {
- boolean a = linesIntersect(x1, y1, x2, y2, x3, y3, x4, y4);
- boolean b = Line2D.Double.linesIntersect(x1, y1, x2, y2, x3, y3, x4, y4);
- System.out.println("ours says " + a + " which is " + (a == expectedResult ? "correct" : "INCORRECT") +
- " / Line2D.Double says " + b + " which is " + (b == expectedResult ? "correct" : "INCORRECT"));
- }
-
- public static void main(String[] args) {
- test(179.2690296114372, 1527.2309703885628, 150.9847583639753, 1498.946699141101, 94.4162158690515, 1442.378156646177, 66.1319446215896, 1414.0938853987152, false);
- test(0, 0, 0, 0, 1, 1, 1, 1, false);
- test(0, 0, 0.5, 0.5, 1, 1, 2, 2, false);
- test(0, 0, 2, 2, 0, 2, 2, 0, true);
- test(0, 0, 2, 2, 4, 0, 3, 2, false);
- }
-}