Box2d对象投掷更平滑，速度相同

我有一个box2d对象，我从上到下，我已经设置了它的速度不变，但是当我运行它，这个对象有时会有不同的速度，我怎样才能使这个对象更平滑。

以下是一些方法来显示我如何创buildbox2d世界和box2d身体对象。

#pragma -mark Box2D World -(void)createWorld { // Define the gravity vector. b2Vec2 b_gravity; b_gravity.Set(0.0f, -9.8f); // Do we want to let bodies sleep? // This will speed up the physics simulation bool doSleep = true; // Construct a world object, which will hold and simulate the rigid bodies. world = new b2World(b_gravity); world->SetAllowSleeping(doSleep); world->SetContinuousPhysics(true); } -(void) createWeb { freeBodySprite = [CCSprite spriteWithFile:@"web1.png"];//web_ani_6_1 //freeBodySprite.position = ccp(100, 300); [self addChild:freeBodySprite z:2 tag:6]; CGPoint startPos = CGPointMake(100, 320/1.25); bodyDef.type = b2_staticBody; bodyDef.position = [self toMeters:startPos]; bodyDef.userData = freeBodySprite; float radiusInMeters = ((freeBodySprite.contentSize.width * freeBodySprite.scale/PTM_RATIO) * 0.5f); shape.m_radius = radiusInMeters; fixtureDef.shape = &shape; fixtureDef.density = 0.07f; fixtureDef.friction = 0.1f; fixtureDef.restitution = 0.1f; circularObstacleBody = world->CreateBody(&bodyDef); stoneFixture = circularObstacleBody->CreateFixture(&fixtureDef); freeBody = circularObstacleBody; } -(b2Vec2) toMeters:(CGPoint)point { return b2Vec2(point.x / PTM_RATIO, point.y / PTM_RATIO); } -(b2Body *) getBodyAtLocation:(b2Vec2) aLocation { for (b2Body* b = world->GetBodyList(); b; b = b->GetNext()) { b2Fixture* bodyFixture = b->GetFixtureList(); if (bodyFixture->TestPoint(aLocation)){ return b; } } return NULL; } -(void) tick: (ccTime) dt { //It is recommended that a fixed time step is used with Box2D for stability //of the simulation, however, we are using a variable time step here. //You need to make an informed choice, the following URL is useful //http://gafferongames.com/game-physics/fix-your-timestep/ int32 velocityIterations = 8; int32 positionIterations = 3; // Instruct the world to perform a single step of simulation. It is // generally best to keep the time step and iterations fixed. world->Step(dt, velocityIterations, positionIterations); //Iterate over the bodies in the physics world for (b2Body* b = world->GetBodyList(); b; b = b->GetNext()) { if (b->GetUserData() != NULL) { //Synchronize the AtlasSprites position and rotation with the corresponding body CCSprite *myActor = (CCSprite*)b->GetUserData(); myActor.position = CGPointMake( b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO); myActor.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle()); } } } 

这是我的触摸事件，我正在获取angular度和速度扔。

 - (void)ccTouchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{ //get the location of the end point of the swipe UITouch *myTouch = [touches anyObject]; CGPoint location = [myTouch locationInView:[myTouch view]]; location = [[CCDirector sharedDirector] convertToGL:location]; //CCLOG(@"Start -> %0.f || End -> %0.f",startPoint.x,location.x); if (freeBody) { //[self calcAngleAndRotateObjectStartingAtPoint:startPoint endingAtPoint:location]; self.isTouchEnabled = NO; freeBody->SetType(b2_dynamicBody); //this is the maximum force that can be applied const CGFloat maxForce = 20; //get the rotation b/w the start point and the end point CGFloat rotAngle = atan2f(location.y - startPoint.y,location.x - startPoint.x); //the distance of the swipe if the force CGFloat distance = ccpDistance(startPoint, location) * 0.5; //if (distance>maxForce) distance = maxForce; //else // distance = 10; //apply force freeBody->ApplyForce(b2Vec2(cosf(rotAngle) * distance, sinf(rotAngle) * distance), freeBody->GetPosition()); //lose the weak reference to the body for next time usage. freeBody = nil; } } 

这是我用来扔的代码，但有时它的速度更快，时间更慢，我已经设置了maxForce = 20的恒定速度。

Answer 1

正如上面的注释world->Step()指示的那样，您应该使用fixed dt 。 validationdt是固定的， world->Step()正在定期调用。

Answer 2

Finnally我已经解决了这个问题。 我用SetLinearVelocity更改了ApplyForce ..

这里是代码。

  float spd = 10; b2Vec2 velocity = spd*b2Vec2(cos(rotAngle), sin(rotAngle)); freeBody->SetLinearVelocity(velocity);