ios - 如何计算b2body对象的行进距离

Question

在我的 cocos2d 项目中，游戏板上有游戏芯片。我使用 b2MouseJoint 在板上移动这个芯片。要移动芯片，我使用以下代码

-(void)ccTouchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{

        if (_mouseJoint == NULL) return;

        UITouch *myTouch = [touches anyObject];
        CGPoint location = [myTouch locationInView:[myTouch view]];
        location = [[CCDirector sharedDirector] convertToGL:location];
        b2Vec2 locationWorld = b2Vec2(location.x/PTM_RATIO, location.y/PTM_RATIO);
        _mouseJoint->SetTarget(locationWorld);


}

- (void)ccTouchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{

        if (_mouseJoint != NULL) return;
        UITouch* touch = [touches anyObject];
        CGPoint startPoint = [[CCDirector sharedDirector] convertToGL:[touch locationInView:[touch view]]];
        b2Vec2 locationWorld = b2Vec2(startPoint.x/PTM_RATIO, startPoint.y/PTM_RATIO);
        _touchedBody = [self getBodyAtLocation:locationWorld];

            if(_touchedBody != NULL)
            {
                b2MouseJointDef md;
                md.bodyA = _groundBody;
                md.bodyB = _touchedBody;
                md.target = locationWorld;
                md.collideConnected = true;
                md.frequencyHz = 4.0f;
                md.maxForce = 900000.0f * _touchedBody->GetMass();
                _mouseJoint = (b2MouseJoint *)_world->CreateJoint(&md);
                _touchedBody->SetAwake(true);

            }         


  }

因此，我需要计算 _touchedBody 的移动距离。请帮我。

Answer 1

只要在调用ccTouchesBegan时存储对象的位置，然后在ccTouchesMoved完成后使用最终位置来计算差异。