Where would I update a graphical representation of a b2Body in Box2D's solver?

Question

Hey i'm trying to make a class called BodyRep Which is supposed to use SFML too sync a graphical representation and Box2D Bodies orientation/location.

To do this i plan to ovveride some Box2D function so that it does it's original steps, plus one extra: to update the graphical representaions orientation based on the new Body orientation.

However I found this is not as easy as it seems as my class must be a descendent of another class that does the actual updates to the bodies in the World, so it CAN ovveride the function. On top of that, I know there is a ton of itterating in Box2D's solver, and i don't want my graphical reps. being updated if they don't have to yet....

So... What CLASS should I Descend from and what FUNCTION should I ovveride?

• if you have any other ideas on how i could accomplish my goal of syncronization between SFML and Box2D bodies, feel free to suggest them! =)

Answer 1

Box2D's body classes are not open for subclassing (nor are most of its other classes). They come out of a factory method on b2World, and they cannot (should not) be copied.

Generally, you should be using composition rather than inheritance:

struct BodyRep {
    b2Body *physics;
    sf::Sprite *visual;
};
....
for (BodyRep &e : drawable_bodies) {
    b2Vec2 pos = e.physics->GetPosition();
    e.visual->SetPosition(pos.x, pos.y);
    // + whatever other properties you need, e.g. size.
    window.Draw(*e.visual);
}