Method for checking if two points are in sight of each other.

Description

Demo Code


//package com.java2s;
import java.awt.geom.Rectangle2D;
import java.util.Collection;

public class Main {


    /**/*w  ww.  j  av a2  s  . com*/
     * Method for checking if two points are in sight of each other. This is
     * done by drawing a line between the two points and checking against the
     * provided obstructionBounds.
     * 
     * @param obstructionBounds
     *            The obstruction that can get in the way
     * @param point1X
     *            first point x position
     * @param point1Y
     *            first point y position
     * @param point2X
     *            second point x position
     * @param point2Y
     *            second point y position
     * @return True if it is possible to "see" from point 1 to point 2.
     */
    public static boolean isInSight(
            Collection<Rectangle2D.Float> obstructionBounds, float point1X,
            float point1Y, float point2X, float point2Y) {
        for (Rectangle2D.Float rect : obstructionBounds) {
            if (recIntersectLine(rect, point1X, point1Y, point2X, point2Y)) {
                return false;
            }
        }
        return true;
    }

    /**
     * Tests if a line from point 1 to point 2 is intersecting the rectangle
     * rect.
     * 
     * @param rect
     *            the Rectangle that maybe intersects
     * @param point1X
     *            x variable of first point
     * @param point1Y
     *            y variable of first point
     * @param point2X
     *            x variable of second point
     * @param point2Y
     *            y variable of second point
     * @return true if line is intersected by rect
     */
    public static boolean recIntersectLine(Rectangle2D.Float rect,
            float point1X, float point1Y, float point2X, float point2Y) {
        return (linesIntersect(point1X, point1Y, point2X, point2Y,
                rect.getX(), rect.getY(), rect.getX() + rect.getWidth(),
                rect.getY() + rect.getHeight()) || linesIntersect(point1X,
                point1Y, point2X, point2Y, rect.getX(),
                rect.getY() + rect.getHeight(),
                rect.getX() + rect.getWidth(), rect.getY()));
    }

    /**
     * 
     * The fastest way to test if 2 line segments intersect. Tests if the line
     * segment from (x1, y1) to (x2, y2) intersects the line segment from (x3,
     * y3) to (x4, y4). My tests showed that this method was about 25% faster
     * than java.awt.geom.Line2D.linesIntersect(x1, y1, x2, y2, x3, y3, x4, y4).
     * 
     * NOTE: This method is taken from java-gaming.org where it was posted by
     * user JGO Knight. For some reason Java default intersect method as
     * declared in the interface Shape doesn't work.
     * 
     * @param x1
     *            Point 1 X
     * @param y1
     *            Point 1 Y
     * @param x2
     *            Point 2 X
     * @param y2
     *            Point 2 Y
     * @param x3
     *            Point 3 X
     * @param y3
     *            Point 3 Y
     * @param x4
     *            Point 4 X
     * @param y4
     *            Point 4 Y
     * @return true if intersect
     */
    private static boolean linesIntersect(double x1, double y1, double x2,
            double y2, double x3, double y3, double x4, double y4) {
        // Return false if either of the lines have zero length
        if (x1 == x2 && y1 == y2 || x3 == x4 && y3 == y4) {
            return false;
        }
        // Fastest method, based on Franklin Antonio's
        // "Faster Line Segment Intersection" topic "in Graphics Gems III" book
        // (http://www.graphicsgems.org/)
        double ax = x2 - x1;
        double ay = y2 - y1;
        double bx = x3 - x4;
        double by = y3 - y4;
        double cx = x1 - x3;
        double cy = y1 - y3;

        double alphaNumerator = by * cx - bx * cy;
        double commonDenominator = ay * bx - ax * by;
        if (commonDenominator > 0) {
            if (alphaNumerator < 0 || alphaNumerator > commonDenominator) {
                return false;
            }
        } else if (commonDenominator < 0) {
            if (alphaNumerator > 0 || alphaNumerator < commonDenominator) {
                return false;
            }
        }
        double betaNumerator = ax * cy - ay * cx;
        if (commonDenominator > 0) {
            if (betaNumerator < 0 || betaNumerator > commonDenominator) {
                return false;
            }
        } else if (commonDenominator < 0) {
            if (betaNumerator > 0 || betaNumerator < commonDenominator) {
                return false;
            }
        }
        if (commonDenominator == 0) {
            // This code wasn't in Franklin Antonio's method. It was added by
            // Keith Woodward.
            // The lines are parallel.
            // Check if they're collinear.
            double y3LessY1 = y3 - y1;
            double collinearityTestForP3 = x1 * (y2 - y3) + x2 * (y3LessY1)
                    + x3 * (y1 - y2); // see
            // http://mathworld.wolfram.com/Collinear.html
            // If p3 is collinear with p1 and p2 then p4 will also be collinear,
            // since p1-p2 is parallel with p3-p4
            if (collinearityTestForP3 == 0) {
                // The lines are collinear. Now check if they overlap.
                if (x1 >= x3 && x1 <= x4 || x1 <= x3 && x1 >= x4
                        || x2 >= x3 && x2 <= x4 || x2 <= x3 && x2 >= x4
                        || x3 >= x1 && x3 <= x2 || x3 <= x1 && x3 >= x2) {
                    if (y1 >= y3 && y1 <= y4 || y1 <= y3 && y1 >= y4
                            || y2 >= y3 && y2 <= y4 || y2 <= y3 && y2 >= y4
                            || y3 >= y1 && y3 <= y2 || y3 <= y1 && y3 >= y2) {
                        return true;
                    }
                }
            }
            return false;
        }
        return true;
    }
}
Method for checking if two points are in sight of each other. - Java java.lang

Description

Demo Code

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