Returns less than zero if p2 is on the left hand side of the line created by p1 and theta and greater than zero if it is on the right hand side. - Java java.lang

Java examples for java.lang:Math Geometry Line

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Description

Returns less than zero if p2 is on the left hand side of the line created by p1 and theta and greater than zero if it is on the right hand side.

Demo Code

// Copyright (C) 2002-2012 Three Rings Design, Inc., All Rights Reserved
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.geom.Point2D;
import static com.threerings.geom.Log.log;

public class Main{
    /**/*from   w ww. j  a va 2 s  . com*/
     * Returns less than zero if <code>p2</code> is on the left hand side of the line created by
     * <code>p1</code> and <code>theta</code> and greater than zero if it is on the right hand
     * side. In theory, it will return zero if the point is on the line, but due to rounding errors
     * it almost always decides that it's not exactly on the line.
     *
     * @param p1 the point on the line whose side we're checking.
     * @param theta the (logical) angle defining the line.
     * @param p2 the point that lies on one side or the other of the line.
     */
    public static int whichSide(Point p1, double theta, Point p2) {
        // obtain the point defining the right hand normal (N)
        theta += Math.PI / 2;
        int x = p1.x + (int) Math.round(1000 * Math.cos(theta)), y = p1.y
                + (int) Math.round(1000 * Math.sin(theta));

        // now dot the vector from p1->p2 with the vector from p1->N, if it's positive, we're on
        // the right hand side, if it's negative we're on the left hand side and if it's zero,
        // we're on the line
        return dot(p1.x, p1.y, p2.x, p2.y, x, y);
    }
    /**
     * Computes and returns the dot product of the two vectors.
     *
     * @param v1s the starting point of the first vector.
     * @param v1e the ending point of the first vector.
     * @param v2s the starting point of the second vector.
     * @param v2e the ending point of the second vector.
     */
    public static int dot(Point v1s, Point v1e, Point v2s, Point v2e) {
        return ((v1e.x - v1s.x) * (v2e.x - v2s.x) + (v1e.y - v1s.y)
                * (v2e.y - v2s.y));
    }
    /**
     * Computes and returns the dot product of the two vectors.  See {@link
     * #dot(Point,Point,Point,Point)} for an explanation of the arguments
     */
    public static int dot(int v1sx, int v1sy, int v1ex, int v1ey, int v2sx,
            int v2sy, int v2ex, int v2ey) {
        return ((v1ex - v1sx) * (v2ex - v2sx) + (v1ey - v1sy)
                * (v2ey - v2sy));
    }
    /**
     * Computes and returns the dot product of the two vectors. The vectors are assumed to start
     * with the same coordinate and end with different coordinates.
     *
     * @param vs the starting point of both vectors.
     * @param v1e the ending point of the first vector.
     * @param v2e the ending point of the second vector.
     */
    public static int dot(Point vs, Point v1e, Point v2e) {
        return ((v1e.x - vs.x) * (v2e.x - vs.x) + (v1e.y - vs.y)
                * (v2e.y - vs.y));
    }
    /**
     * Computes and returns the dot product of the two vectors.  See {@link
     * #dot(Point,Point,Point)} for an explanation of the arguments
     */
    public static int dot(int vsx, int vsy, int v1ex, int v1ey, int v2ex,
            int v2ey) {
        return ((v1ex - vsx) * (v2ex - vsx) + (v1ey - vsy) * (v2ey - vsy));
    }
}

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