axmol/Box2D/Dynamics/b2ContactManager.cpp

/*
* Copyright (c) 2006-2009 Erin Catto http://www.box2d.org
*
* This software is provided 'as-is', without any express or implied
* warranty.  In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

#include <Box2D/Dynamics/b2ContactManager.h>
#include <Box2D/Dynamics/b2Body.h>
#include <Box2D/Dynamics/b2Fixture.h>
#include <Box2D/Dynamics/b2WorldCallbacks.h>
#include <Box2D/Dynamics/Contacts/b2Contact.h>

b2ContactFilter b2_defaultFilter;
b2ContactListener b2_defaultListener;

b2ContactManager::b2ContactManager()
{
    m_contactList = NULL;
    m_contactCount = 0;
    m_contactFilter = &b2_defaultFilter;
    m_contactListener = &b2_defaultListener;
    m_allocator = NULL;
}

void b2ContactManager::Destroy(b2Contact* c)
{
    b2Fixture* fixtureA = c->GetFixtureA();
    b2Fixture* fixtureB = c->GetFixtureB();
    b2Body* bodyA = fixtureA->GetBody();
    b2Body* bodyB = fixtureB->GetBody();

    if (m_contactListener && c->IsTouching())
    {
        m_contactListener->EndContact(c);
    }

    // Remove from the world.
    if (c->m_prev)
    {
        c->m_prev->m_next = c->m_next;
    }

    if (c->m_next)
    {
        c->m_next->m_prev = c->m_prev;
    }

    if (c == m_contactList)
    {
        m_contactList = c->m_next;
    }

    // Remove from body 1
    if (c->m_nodeA.prev)
    {
        c->m_nodeA.prev->next = c->m_nodeA.next;
    }

    if (c->m_nodeA.next)
    {
        c->m_nodeA.next->prev = c->m_nodeA.prev;
    }

    if (&c->m_nodeA == bodyA->m_contactList)
    {
        bodyA->m_contactList = c->m_nodeA.next;
    }

    // Remove from body 2
    if (c->m_nodeB.prev)
    {
        c->m_nodeB.prev->next = c->m_nodeB.next;
    }

    if (c->m_nodeB.next)
    {
        c->m_nodeB.next->prev = c->m_nodeB.prev;
    }

    if (&c->m_nodeB == bodyB->m_contactList)
    {
        bodyB->m_contactList = c->m_nodeB.next;
    }

    // Call the factory.
    b2Contact::Destroy(c, m_allocator);
    --m_contactCount;
}

// This is the top level collision call for the time step. Here
// all the narrow phase collision is processed for the world
// contact list.
void b2ContactManager::Collide()
{
    // Update awake contacts.
    b2Contact* c = m_contactList;
    while (c)
    {
        b2Fixture* fixtureA = c->GetFixtureA();
        b2Fixture* fixtureB = c->GetFixtureB();
        int32 indexA = c->GetChildIndexA();
        int32 indexB = c->GetChildIndexB();
        b2Body* bodyA = fixtureA->GetBody();
        b2Body* bodyB = fixtureB->GetBody();
         
        // Is this contact flagged for filtering?
        if (c->m_flags & b2Contact::e_filterFlag)
        {
            // Should these bodies collide?
            if (bodyB->ShouldCollide(bodyA) == false)
            {
                b2Contact* cNuke = c;
                c = cNuke->GetNext();
                Destroy(cNuke);
                continue;
            }

            // Check user filtering.
            if (m_contactFilter && m_contactFilter->ShouldCollide(fixtureA, fixtureB) == false)
            {
                b2Contact* cNuke = c;
                c = cNuke->GetNext();
                Destroy(cNuke);
                continue;
            }

            // Clear the filtering flag.
            c->m_flags &= ~b2Contact::e_filterFlag;
        }

        bool activeA = bodyA->IsAwake() && bodyA->m_type != b2_staticBody;
        bool activeB = bodyB->IsAwake() && bodyB->m_type != b2_staticBody;

        // At least one body must be awake and it must be dynamic or kinematic.
        if (activeA == false && activeB == false)
        {
            c = c->GetNext();
            continue;
        }

        int32 proxyIdA = fixtureA->m_proxies[indexA].proxyId;
        int32 proxyIdB = fixtureB->m_proxies[indexB].proxyId;
        bool overlap = m_broadPhase.TestOverlap(proxyIdA, proxyIdB);

        // Here we destroy contacts that cease to overlap in the broad-phase.
        if (overlap == false)
        {
            b2Contact* cNuke = c;
            c = cNuke->GetNext();
            Destroy(cNuke);
            continue;
        }

        // The contact persists.
        c->Update(m_contactListener);
        c = c->GetNext();
    }
}

void b2ContactManager::FindNewContacts()
{
    m_broadPhase.UpdatePairs(this);
}

void b2ContactManager::AddPair(void* proxyUserDataA, void* proxyUserDataB)
{
    b2FixtureProxy* proxyA = (b2FixtureProxy*)proxyUserDataA;
    b2FixtureProxy* proxyB = (b2FixtureProxy*)proxyUserDataB;

    b2Fixture* fixtureA = proxyA->fixture;
    b2Fixture* fixtureB = proxyB->fixture;

    int32 indexA = proxyA->childIndex;
    int32 indexB = proxyB->childIndex;

    b2Body* bodyA = fixtureA->GetBody();
    b2Body* bodyB = fixtureB->GetBody();

    // Are the fixtures on the same body?
    if (bodyA == bodyB)
    {
        return;
    }

    // TODO_ERIN use a hash table to remove a potential bottleneck when both
    // bodies have a lot of contacts.
    // Does a contact already exist?
    b2ContactEdge* edge = bodyB->GetContactList();
    while (edge)
    {
        if (edge->other == bodyA)
        {
            b2Fixture* fA = edge->contact->GetFixtureA();
            b2Fixture* fB = edge->contact->GetFixtureB();
            int32 iA = edge->contact->GetChildIndexA();
            int32 iB = edge->contact->GetChildIndexB();

            if (fA == fixtureA && fB == fixtureB && iA == indexA && iB == indexB)
            {
                // A contact already exists.
                return;
            }

            if (fA == fixtureB && fB == fixtureA && iA == indexB && iB == indexA)
            {
                // A contact already exists.
                return;
            }
        }

        edge = edge->next;
    }

    // Does a joint override collision? Is at least one body dynamic?
    if (bodyB->ShouldCollide(bodyA) == false)
    {
        return;
    }

    // Check user filtering.
    if (m_contactFilter && m_contactFilter->ShouldCollide(fixtureA, fixtureB) == false)
    {
        return;
    }

    // Call the factory.
    b2Contact* c = b2Contact::Create(fixtureA, indexA, fixtureB, indexB, m_allocator);
    if (c == NULL)
    {
        return;
    }

    // Contact creation may swap fixtures.
    fixtureA = c->GetFixtureA();
    fixtureB = c->GetFixtureB();
    indexA = c->GetChildIndexA();
    indexB = c->GetChildIndexB();
    bodyA = fixtureA->GetBody();
    bodyB = fixtureB->GetBody();

    // Insert into the world.
    c->m_prev = NULL;
    c->m_next = m_contactList;
    if (m_contactList != NULL)
    {
        m_contactList->m_prev = c;
    }
    m_contactList = c;

    // Connect to island graph.

    // Connect to body A
    c->m_nodeA.contact = c;
    c->m_nodeA.other = bodyB;

    c->m_nodeA.prev = NULL;
    c->m_nodeA.next = bodyA->m_contactList;
    if (bodyA->m_contactList != NULL)
    {
        bodyA->m_contactList->prev = &c->m_nodeA;
    }
    bodyA->m_contactList = &c->m_nodeA;

    // Connect to body B
    c->m_nodeB.contact = c;
    c->m_nodeB.other = bodyA;

    c->m_nodeB.prev = NULL;
    c->m_nodeB.next = bodyB->m_contactList;
    if (bodyB->m_contactList != NULL)
    {
        bodyB->m_contactList->prev = &c->m_nodeB;
    }
    bodyB->m_contactList = &c->m_nodeB;

    // Wake up the bodies
    bodyA->SetAwake(true);
    bodyB->SetAwake(true);

    ++m_contactCount;
}