Box2D Joints

1. Mouse Joint

-(BOOL) ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event {
    CGPoint touchLocation = [touch locationInView:[touch view]];
    touchLocation = [[CCDirector sharedDirector]

        convertToGL:touchLocation];
    touchLocation = [self convertToNodeSpace:touchLocation];
    b2Vec2 locationWorld =

        b2Vec2(touchLocation.x/PTM_RATIO, touchLocation.y/PTM_RATIO);

    b2AABB aabb;
    b2Vec2 delta = b2Vec2(1.0/PTM_RATIO, 1.0/PTM_RATIO);
    aabb.lowerBound = locationWorld - delta;
    aabb.upperBound = locationWorld + delta;
    SimpleQueryCallback callback(locationWorld);
    world->QueryAABB(&callback, aabb);

if (callback.fixtureFound) {
        b2Body *body = callback.fixtureFound->GetBody();
        b2MouseJointDef mouseJointDef;
        mouseJointDef.bodyA = groundBody;
        mouseJointDef.bodyB = body;
        mouseJointDef.target = locationWorld;
        mouseJointDef.maxForce = 50 * body->GetMass();
        mouseJointDef.collideConnected = true;

        mouseJoint = (b2MouseJoint *)
            world->CreateJoint(&mouseJointDef);

        body->SetAwake(true);

return YES; }

    return TRUE;
}

-(void) ccTouchMoved:(UITouch *)touch withEvent:(UIEvent *)event {
    CGPoint touchLocation = [touch locationInView:[touch view]];
    touchLocation = [[CCDirector sharedDirector]

        convertToGL:touchLocation];
    touchLocation = [self convertToNodeSpace:touchLocation];
    b2Vec2 locationWorld = b2Vec2(touchLocation.x/PTM_RATIO,

        touchLocation.y/PTM_RATIO);

    if (mouseJoint) {
        mouseJoint->SetTarget(locationWorld);

} }

-(void) ccTouchEnded:(UITouch *)touch withEvent:(UIEvent *)event {
     if (mouseJoint) {

        world->DestroyJoint(mouseJoint);

        mouseJoint = NULL;
     }

}

        2. Revolute Joint  

    wheelL = [Box2DSprite spriteWithSpriteFrameName:@"Wheel.png"];

    wheelL.gameObjectType = kCartType;

    wheelLBody = [self createWheelWithSprite:wheelL

                                      offset:b2Vec2(-63.0/100.0, -48.0/100.0)];

   

    b2RevoluteJointDef revJointDef;

    revJointDef.Initialize(body, wheelLBody,

                           wheelLBody->GetWorldCenter());

   

    revJointDef.enableMotor = true;

    revJointDef.maxMotorTorque = 1000;

    revJointDef.motorSpeed = 0;

//restrict revolute joints to a certain angle range with Box2D

revJointDef.lowerAngle = CC_DEGREES_TO_RADIANS(-30);

revJointDef.upperAngle = CC_DEGREES_TO_RADIANS(60);

revJointDef.enableLimit = true;

 ///////////////////////

    wheelLJoint = (b2RevoluteJoint *) world->CreateJoint(&revJointDef);


        3. Prismatic Joint

A prismatic joint is a type of joint that restricts two bodies so they can move relative to each other only along a specified axis. 

   b2PrismaticJointDef prisJointDef;

    prisJointDef.Initialize(body, legsBody,

                            legsBody->GetWorldCenter(), axis);

    prisJointDef.enableLimit = true;

    prisJointDef.lowerTranslation = 0.0;

    prisJointDef.upperTranslation = 43.0/100.0;

    world->CreateJoint(&prisJointDef);