b2身体问题

Question

I have 2 questions with b2Body:

1. What is the difference between b2Body and b2BodyDef?
2. How would I add a b2Body to a CCScene with coordinates from a CGRect which I already have coded? Also how would I add userData to it so I can keep a reference to this?

Thanks!

Answer 1

A b2BodyDef is used to define information about a body as a whole, such as position and rotation. Compared to the other information you require for a b2Body , such as friction and resititution , that is defined on a per fixture basis using b2Fixtures . The b2Body is an amalgamation of a body definition and at least one fixture.

With regard to creating the body from a predefined rect, I'd advise using setAsBox: assuming you are using a b2PolygonShape .

The way I usually accomplish the joining of the two is to create a class called BodyNode which has ivars of a b2Body and a CCSprite . Assign either the BodyNode , ie self or the sprite as the userData and update them as follows:

-(void) onEnter
{
    [self scheduleUpdate];
    [super onEnter];
}

-(void) update:(ccTime) dt
{
    //Update the position of the sprite to the position of the body
    //Update the rotation of the body to the rotation of the sprite. Take care to note that the rotation of the sprite is in degrees whereas the rotation of the body is in radians.
}