box2d身体旋转

Question

I have a gesture recignizer, and I need to rotate a body:

- (void) rotate:(UIGestureRecognizer*)recognizer node:(CCNode*)node
{
    b2Body *body = (b2Body*)[node.parent userData];
    UIRotationGestureRecognizer* rotate = (UIRotationGestureRecognizer*)recognizer;
    b2Vec2 pos = body->GetPosition();
    body->SetTransform(pos,   (- rotate.rotation));

}

offcorse, when I starting rotation, it starts from zero angle. * But how to continue rotation from current angle? * I cant just add rotate.rotation to tu current angle: this method called on every move, and angle is calculated from very begining of gesture. keep track on actual current angle (without anctive gesture's angle), will be a pretty hard task, I think

Answer 1

I found solution: I checked state of gesture (there is a begining state):

- (void) rotate:(UIGestureRecognizer*)recognizer node:(CCNode*)node
{
    b2Body *body = (b2Body*)[node.parent userData];
    UIRotationGestureRecognizer* rotate = (UIRotationGestureRecognizer*)recognizer;
    if (rotate.state == UIGestureRecognizerStateBegan)
    {
        baseAngle = body->GetAngle();
    }
    b2Vec2 pos = body->GetPosition();
    body->SetTransform(pos,   (baseAngle - rotate.rotation));

}