ColliderPolygon.java

/*
 *  Flingbox - An OpenSource physics sandbox for Google's Android
 *  Copyright (C) 2009  Jon Ander Peñalba & Endika Gutiérrez
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package edu.eside.flingbox.physics.collisions;

import edu.eside.flingbox.math.Intersect;
import edu.eside.flingbox.math.Matrix22;
import edu.eside.flingbox.math.Vector2D;
import edu.eside.flingbox.physics.PhysicBody;
import edu.eside.flingbox.physics.PhysicBody.OnMovementListener;

/**
 * Collider for a polygon. it handles all functions needed by Collision system
 * NOTE This class should only be created by {@link PhisicPolygon}.
 * 
 * How collision detector optimizer works: - When created collider check each
 * polygon's vertex angle and stores them. - When bounding circle collides
 * Collider checks only segments in other circle region.
 * 
 */
public class ColliderPolygon extends Collider implements OnMovementListener {
    /** Handled in Physics, only pointer */
    private final Vector2D[] mPolygonContour;
    /** Located and rotated contour */
    private final Vector2D[] mLocatedContour;

    /**
     * Default constructor for a polygon collider.
     * 
     * @param contour
     *            Polygon's points. It handles pointer in order to preserve
     *            recurses, so mPolygonContour should be automatically rotated.
     *            NOTE It has to be in counterclockwise ordering!!!
     * 
     * @return
     */
    public ColliderPolygon(final Vector2D[] contour, PhysicBody thisPhysic) {
        super(thisPhysic);
        final int pointsCount = contour.length;
        mPolygonContour = contour;
        mRadius = computeBoundingCircleRadius(contour);
        mLocatedContour = new Vector2D[pointsCount];

        for (int i = 0; i < pointsCount; i++)
            mLocatedContour[i] = new Vector2D();

    }

    /**
	 * 
	 */
    public Contact[] checkContacts(final Collider collider) {
        if (!super.canContact(collider))
            return new Contact[0];

        final Vector2D[] polygon = updateLocatedPolygon();
        final Vector2D[] otherPolygon = ((ColliderPolygon) collider)
                .updateLocatedPolygon();

        /* Find intersections */
        // Intersect[] intersections = Intersect.intersectPolygons(polygon,
        // otherPolygon);
        Intersect[] intersections = Intersect.intersectPolygons(polygon,
                otherPolygon);

        /* Compute detected intersections */
        Contact[] contacts = new Contact[intersections.length];
        for (int i = intersections.length - 1; i >= 0; i--) {
            Intersect intersect = intersections[i];
            Vector2D position = new Vector2D(intersect.outgoingPoint).add(
                    intersect.ingoingPoint).mul(0.5f);
            Vector2D sense = new Vector2D(intersect.outgoingPoint)
                    .sub(intersect.ingoingPoint);

            contacts[i] = new Contact(this.mPhysicBody, collider.mPhysicBody,
                    position, sense, intersect);
        }
        return contacts;
    }

    /**
     * Computes bounding circle with center in point (0, 0)
     * 
     * @param contour
     *            Polygon's contour
     * @return Circles radius
     */
    private static float computeBoundingCircleRadius(final Vector2D[] contour) {
        float radiusSquare = 0.0f;
        for (int i = contour.length - 1; i >= 0; i--) { // Do not use fast
                                                        // enumeration since
                                                        // performance issues
            final Vector2D v = contour[i];
            float vRadSquare = (v.i * v.i) + (v.j * v.j);
            if (vRadSquare > radiusSquare)
                radiusSquare = vRadSquare;
        }
        return (float) Math.sqrt(radiusSquare);
    }

    /**
     * Moves polygon to determinate point and rotates it
     * 
     * @return New translated polygon
     */
    private Vector2D[] updateLocatedPolygon() {
        final Vector2D[] polygon = mPolygonContour;
        final Vector2D[] locatedPolygon = mLocatedContour;
        final Vector2D position = mPosition;
        final float angle = mAngle;
        final int pointsCount = polygon.length;
        final Matrix22 rotationMatrix = new Matrix22(angle);

        for (int i = 0; i < pointsCount; i++)
            locatedPolygon[i].set(polygon[i]).mul(rotationMatrix).add(position);

        return locatedPolygon;
    }

}