CODEWITHSUNDEEP
ioscocos2d-iphonebox2dbox2d-iphone
soleil
soleil

Reputation: 13083

Box2d and Cocos2d on iOS issues with sprites and positioning

I am creating new sprites/bodies when touching the screen:

-(void) addNewSpriteAtPosition:(CGPoint)pos
{
    b2BodyDef bodyDef;
    bodyDef.type = b2_dynamicBody;
    bodyDef.position=[Helper toMeters:pos];
    b2Body* body = world->CreateBody(&bodyDef);

    b2CircleShape circle;
    circle.m_radius = 30/PTM_RATIO;

    // Define the dynamic body fixture.
    b2FixtureDef fixtureDef;
    fixtureDef.shape=&circle;
    fixtureDef.density=0.7f;
    fixtureDef.friction=0.3f;
    fixtureDef.restitution = 0.5;
    body-> CreateFixture(&fixtureDef);

    PhysicsSprite* sprite = [PhysicsSprite spriteWithFile:@"circle.png"];
    [self addChild:sprite];
    [sprite setPhysicsBody:body];
    body->SetUserData((__bridge void*)sprite);
}

Here is my positioning helper:

+(b2Vec2) toMeters:(CGPoint)point
{
    return b2Vec2(point.x / PTM_RATIO, point.y / PTM_RATIO);
}

PhysicsSprite is the typical one used with Box2D, but I'll include the relevant method:

-(CGAffineTransform) nodeToParentTransform
{
    b2Vec2 pos = physicsBody->GetPosition();

    float x = pos.x * PTM_RATIO;
    float y = pos.y * PTM_RATIO;

    if (ignoreAnchorPointForPosition_)
    {
        x += anchorPointInPoints_.x;
        y += anchorPointInPoints_.y;
    }

    float radians = physicsBody->GetAngle();
    float c = cosf(radians);
    float s = sinf(radians);

    if (!CGPointEqualToPoint(anchorPointInPoints_, CGPointZero))
    {
        x += c * -anchorPointInPoints_.x + -s * -anchorPointInPoints_.y;
        y += s * -anchorPointInPoints_.x + c * -anchorPointInPoints_.y;
    }

    self.position = CGPointMake(x, y);

    // Rot, Translate Matrix
    transform_ = CGAffineTransformMake(c, s, -s, c, x, y);
    return transform_;
}

Now, I have two issues illustrated by the following two images, which show the debug draw with the sprites. Retina and non-retina versions:

retina

non-retina

Issue #1 - As you can see in both images, the further away from (0,0) the objects are, the sprite becomes further offset from the physics body.

Issue #2 - The red circle image files are 60x60 (retina), and the white circles are 30x30 (non-retina). Why are they sized differently on screen? Cocos2d should use points, not pixels, so shouldn't they be the same size on screen?

Upvotes: 1

Views: 1189

Answers (1)

Guru
Guru

Reputation: 22042

Instead of hardcoded size, use contentSize.

circle.m_radius = sprite.contentSize.width*0.5f/PTM_RATIO;

This works in all SD and Retina mode.

You can use this style to sync between box2d and cocos2d positions:

body->SetTransform([self toB2Meters:sprite.position], 0.0f);    //box2d<---cocos2d

//OR
sprite.position = ccp(body->GetPosition().x * PTM_RATIO,
                     body->GetPosition().y * PTM_RATIO);  //box2d--->cocos2d

Upvotes: 2

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