Arbiter.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 java.util.ArrayList;
import java.util.Collections;
import java.util.ConcurrentModificationException;

import android.util.Log;

import edu.eside.flingbox.physics.PhysicBody;
import edu.eside.flingbox.utils.PositionComparator;

/**
 * Arbiter manages the collisions between bodies
 */
public class Arbiter {

    /** List with all colliders on the scene */
    private final ArrayList<Collider> mCollisionableBodies = new ArrayList<Collider>();

    /** Adds new collider to the arbiter */
    public void add(final Collider collider) {
        mCollisionableBodies.add(collider);
    }

    /** Removes a collider from the arbiter */
    public boolean remove(final Collider collider) {
        return mCollisionableBodies.remove(collider);
    }

    /**
     * Checks collision between bodies that are managed by the arbiter.
     * 
     * @return number of collisions
     */
    public void checkCollisions() {
        final ArrayList<Collider> bodies = mCollisionableBodies;
        final ArrayList<Contact> contactsToSolve = new ArrayList<Contact>();
        final int bodiesCount = bodies.size();

        /* Start checking movable objects */
        for (int i = bodiesCount - 1; i >= 0; i--)
            for (int j = i - 1; j >= 0; j--) {
                Contact[] contacts = bodies.get(i).checkContacts(bodies.get(j));
                for (Contact contact : contacts)
                    contactsToSolve.add(contact);
            }
        /* Sort contacts to solve those */
        Collections.sort(contactsToSolve, PositionComparator.UPPER_COMPARATOR);

        final ArrayList<Contact> isolatedContactTree = new ArrayList<Contact>();

        while (!contactsToSolve.isEmpty()) {
            isolatedContactTree.clear();
            Contact treeRoot = contactsToSolve.get(0); // get top contact
            contactsToSolve.remove(0);
            isolatedContactTree.add(treeRoot);

            getIsolatedContactsTree(treeRoot.collidedBody, contactsToSolve,
                    isolatedContactTree);
            getIsolatedContactsTree(treeRoot.collidingBody, contactsToSolve,
                    isolatedContactTree);

            solveIsolatedContactTree(isolatedContactTree);
        }

    }

    private void solveIsolatedContactTree(
            final ArrayList<Contact> isolatedContacts) {
        // Vector2D totalImpulse = new Vector2D();
        for (Contact contact : isolatedContacts) {
            ContactSolver.solveCollision(contact);
            ContactSolver.solvePenetration(contact);
        }
        for (int i = isolatedContacts.size() - 2; i >= 0; i--) {
            ContactSolver.solveCollision(isolatedContacts.get(i));
            ContactSolver.solvePenetration(isolatedContacts.get(i));
        }

    }

    private void getIsolatedContactsTree(final PhysicBody rootBody,
            final ArrayList<Contact> contacts,
            ArrayList<Contact> isolatedContacts) {
        try {
            for (int i = 0; i < contacts.size(); i++) {
                Contact contact = contacts.get(i);
                if (contact.concerns(rootBody)) {
                    contacts.remove(contact);
                    i--;
                    isolatedContacts.add(contact);
                    getIsolatedContactsTree(contact.otherBody(rootBody),
                            contacts, isolatedContacts);
                }
            }
        } catch (ConcurrentModificationException ex) {
            Log
                    .e(
                            "flingbox",
                            "ConcurrentModificationException getting isolated contacts tree",
                            ex);
        }

    }
}