CODEWITHSUNDEEP
cocos2d-iphonebox2dscale
nick
nick

Reputation: 19784

Box2D object speed

I have a little issue with my game. In my main game scene I create a Player object from a class, like this:

player = [Player spriteWithFile:@"[email protected]"];        
player.position = ccp(100.0f, 180.0f);
[player createBox2dObject:world];

Below is the main chunk of my small Player class that creates the body and the fixture so I can use it in a box2d world.

b2BodyDef playerBodyDef;
playerBodyDef.type = b2_dynamicBody;
playerBodyDef.position.Set(self.position.x/PTM_RATIO, self.position.y/PTM_RATIO);
playerBodyDef.userData = self;
playerBodyDef.fixedRotation = true;
playerBodyDef.linearDamping = 4.0;

body = world->CreateBody(&playerBodyDef);

b2CircleShape circleShape;
circleShape.m_radius = 0.7;
b2FixtureDef fixtureDef;
fixtureDef.shape = &circleShape;
fixtureDef.density = 1.0f;
fixtureDef.friction = 1.0f;
fixtureDef.restitution =  1.0f;

body->CreateFixture(&fixtureDef);

The result of this code is a Box2d object with [email protected] over it. When I move a joystick, a Box2D impulse is applied and the player moves. Simple enough, right? In non-retina displays, this works fine. However, when I switch to Retina in the simulator, [email protected] is created a little higher and farther to the right, not over the Box2D circle. Then, gravity is applied and they both fall down to the platform. [email protected] falls twice as fast. When I move the joystick, the Box2D circle moves, but [email protected] moves twice as fast and the camera follows it, soon leaving the circle off the screen. I doubt this issue has really anything to do with the code I have here, I feel like its a scaling issue hidden somewhere in my game. Does anyone have suggestions?

Edit: I move the sprite with:

[player moveRight];

This is moveRight in the player class:

-(void) moveRight {
    b2Vec2 impulse = b2Vec2(2.0f, 0.0f);
    body->ApplyLinearImpulse(impulse, body->GetWorldCenter());
}

Shouldn't be any issue here, right?

Edit (again):

Here's my update: method- 

- (void) update:(ccTime)dt {
    int32 velocityIterations = 8;
    int32 positionIterations = 1;

    world->Step(dt, velocityIterations, positionIterations);

    for (b2Body* b = world->GetBodyList(); b; b = b->GetNext()) {
        if (b->GetUserData() != NULL) {
            CCSprite *myActor = (CCSprite*)b->GetUserData();
            myActor.position = CGPointMake( b->GetPosition().x *PTM_RATIO, 
                                       b->GetPosition().y * PTM_RATIO);
            myActor.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
        }   
    }
    b2Vec2 pos = [player body]->GetPosition();
    CGPoint newPos = ccp(-1 * pos.x * PTM_RATIO + 50, self.position.y * PTM_RATIO); 
    [self setPosition:newPos];
}

I have a feeling that the issue is somewhere in here. I've tried changing PTM_RATIO around, but it doesn't affect the speed. Any ideas?

Edit: see comment below, almost have this figured out

Upvotes: 0

Views: 1045

Answers (1)

Jer In Chicago
Jer In Chicago

Reputation: 828

You problem probably stems from the fact you are using a @2x image... Read, http://www.cocos2d-iphone.org/wiki/doku.php/prog_guide:how_to_develop_retinadisplay_games_in_cocos2d

There it states:

WARNING: It is NOT recommend to use the ”@2x” suffix. Apple treats those images in a special way which might cause bugs in your cocos2d application.

So to solve your problem read through the information on using png files with the -hd suffix.

For the comment:

Do you have some code that looks something like...

  world->Step(dt, 10, 10);
  for(b2Body *b = world->GetBodyList(); b; b=b->GetNext()) {    
    if (b->GetUserData() != NULL) {
      CCSprite *sprite = (CCSprite *)b->GetUserData();
      sprite.position = ccp(b->GetPosition().x * PTM_RATIO,b->GetPosition().y * PTM_RATIO);
    }
  }

See how the code loops through all the box2d bodies in the word and sets the position of the sprite that is associated with the box2d body?

Upvotes: 1

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