ingo@3227: package de.intevation.flys.artifacts.geom;
sascha@1797: 
sascha@1797: import java.awt.geom.Point2D;
sascha@1797: 
sascha@1797: public final class VectorUtils
sascha@1797: {
sascha@1797:     public static final double EPSILON = 1e-4;
sascha@1797: 
sascha@1797:     private VectorUtils() {
sascha@1797:     }
sascha@1797: 
sascha@1799:     public static final double X(Point2D p) {
sascha@1797:         return p.getX();
sascha@1797:     }
sascha@1797: 
sascha@1799:     public static final double Y(Point2D p) {
sascha@1797:         return p.getY();
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final Point2D sub(Point2D a, Point2D b) {
sascha@1797:         return new Point2D.Double(X(a)-X(b), Y(a)-Y(b));
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final double dot(Point2D a, Point2D b) {
sascha@1797:         return X(a)*X(b) + Y(a)*Y(b);
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final Point2D add(Point2D a, Point2D b) {
sascha@1797:         return new Point2D.Double(X(a)+X(b), Y(a)+Y(b));
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final Point2D negate(Point2D a) {
sascha@1797:         return new Point2D.Double(-X(a), -Y(a));
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final Point2D ortho(Point2D a) {
sascha@1797:         return new Point2D.Double(-Y(a), X(a));
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final Point2D scale(Point2D a, double s) {
sascha@1797:         return new Point2D.Double(s*X(a), s*Y(a));
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final double lengthSq(Point2D a) {
sascha@1797:         double x = X(a);
sascha@1797:         double y = Y(a);
sascha@1797:         return x*x + y*y;
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final double length(Point2D a) {
sascha@1797:         return Math.sqrt(lengthSq(a));
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final Point2D normalize(Point2D a) {
sascha@1797:         double length = length(a);
sascha@1797:         return length != 0d
sascha@3076:             ? scale(a, 1d/length)
sascha@1797:             : new Point2D.Double(X(a), Y(a));
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final double L1(Point2D a, Point2D b) {
sascha@1797:         return Math.abs(X(a)-X(b)) + Math.abs(Y(a)-Y(b));
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static final boolean collinear(Point2D a, Point2D b, Point2D c) {
sascha@1797:         double x1 = X(a);
sascha@1797:         double y1 = Y(a);
sascha@1797:         double x2 = X(b);
sascha@1797:         double y2 = Y(b);
sascha@1797:         double x3 = X(c);
sascha@1797:         double y3 = Y(c);
sascha@1797: 
sascha@1797:         return Math.abs((x2-x1)*(y3-y1)-(y2-y1)*(x3-x1)) < EPSILON;
sascha@1797:     }
sascha@1797: 
sascha@1797:     public static boolean epsilonEquals(Point2D a, Point2D b) {
sascha@3076:         return Math.abs(X(a)-X(b)) < EPSILON
sascha@1797:             && Math.abs(Y(a)-Y(b)) < EPSILON;
sascha@1797:     }
sascha@1797: 
sascha@1801:     public static final Point2D intersection(
sascha@1801:         Point2D p1, Point2D p2,
sascha@1801:         Point2D p3, Point2D p4
sascha@1801:     ) {
sascha@1801:         double x1 = X(p1);
sascha@1801:         double y1 = Y(p1);
sascha@1801:         double x2 = X(p2);
sascha@1801:         double y2 = Y(p2);
sascha@1801:         double x3 = X(p3);
sascha@1801:         double y3 = Y(p3);
sascha@1801:         double x4 = X(p4);
sascha@1801:         double y4 = Y(p4);
sascha@1801: 
sascha@1801:         // Compute a1, b1, c1, where line joining points 1 and 2
sascha@1801:         // is "a1 x + b1 y + c1 = 0".
sascha@1801:         double a1 = y2 - y1;
sascha@1801:         double b1 = x1 - x2;
sascha@1801:         double c1 = x2*y1 - x1*y2;
sascha@1801: 
sascha@1801:         // Compute r3 and r4.
sascha@1801:         double r3 = a1*x3 + b1*y3 + c1;
sascha@1801:         double r4 = a1*x4 + b1*y4 + c1;
sascha@1801: 
sascha@1801:         if (r3 != 0d && r4 != 0d && r3*r4 >= 0) {
sascha@1801:             return null;
sascha@1801:         }
sascha@1801: 
sascha@1801:         // Compute a2, b2, c2
sascha@1801:         double a2 = y4 - y3;
sascha@1801:         double b2 = x3 - x4;
sascha@1801:         double c2 = (x4 * y3) - (x3 * y4);
sascha@1801: 
sascha@1801:         // Compute r1 and r2
sascha@1801:         double r1 = a2*x1 + b2*y1 + c2;
sascha@1801:         double r2 = a2*x2 + b2*y2 + c2;
sascha@1801: 
sascha@1801:         if (r1 != 0d && r2 != 0d && r1*r2 >= 0) {
sascha@1801:             return null;
sascha@1801:         }
sascha@1801: 
sascha@1801:         // Line segments intersect: compute intersection point.
sascha@1801:         double denom = a1*b2 - a2*b1;
sascha@1801: 
sascha@1801:         if (denom == 0d) { // collinear
sascha@1801:             return null;
sascha@1801:         }
sascha@1801: 
sascha@1801:         double offset = Math.abs(denom)/2d;
sascha@1801: 
sascha@1801:         // The denom/2 is to get rounding instead of truncating. It
sascha@1801:         // is added or subtracted to the numerator, depending upon the
sascha@1801:         // sign of the numerator.
sascha@1801:         double num = b1*c2 - b2*c1;
sascha@1801: 
sascha@1801:         double x = num < 0d
sascha@1801:             ? (num - offset)/denom
sascha@1801:             : (num + offset)/denom;
sascha@1801: 
sascha@1801:         num = a2*c1 - a1*c2;
sascha@1801: 
sascha@1801:         double y = num < 0d
sascha@1801:             ? (num - offset)/denom
sascha@1801:             : (num + offset)/denom;
sascha@1801: 
sascha@1801:         return new Point2D.Double(x, y);
sascha@1801:     }
sascha@1801: 
sascha@1797: }
sascha@3076: // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :