Question

我在iOS cocos2d应用程序上使用80个Box2d对象运行40 FPS。我正在使用固定的时间步长：

-(void) update: (ccTime) dt
{
if( gameState_ != kGameStatePaused ) {
world_->Step(dt, 6, 1 );

....
}

为什么会这样？感谢。

Answer 1

这是一个更好的固定时间步骤：

//FIX TIME STEP
///////--->>>>>>>>>>>>>
const float32 FIXED_TIMESTEP = 1.0f / 60.0f;

// Minimum remaining time to avoid box2d unstability caused by very small delta times
// if remaining time to simulate is smaller than this, the rest of time will be added to the last step,
// instead of performing one more single step with only the small delta time.
const float32 MINIMUM_TIMESTEP = 1.0f / 600.0f;  

const int32 VELOCITY_ITERATIONS = 8;
const int32 POSITION_ITERATIONS = 8;

// maximum number of steps per tick to avoid spiral of death
const int32 MAXIMUM_NUMBER_OF_STEPS = 25;
///////<<<<<<<<<<<<<<<<<<-------------------

//FIX TIME STEP----------->>>>>>>>>>>>>>>>
-(void)afterStep {

     // process collisions and result from callbacks called by the step
}


-(void)step:(ccTime)dt {
    float32 frameTime = dt;
    int stepsPerformed = 0;
    while ( (frameTime > 0.0) && (stepsPerformed < MAXIMUM_NUMBER_OF_STEPS) ){
        float32 deltaTime = std::min( frameTime, FIXED_TIMESTEP );
        frameTime -= deltaTime;
        if (frameTime < MINIMUM_TIMESTEP) {
            deltaTime += frameTime;
            frameTime = 0.0f;
        }
        world->Step(deltaTime,VELOCITY_ITERATIONS,POSITION_ITERATIONS);
        stepsPerformed++;
        [self afterStep]; // process collisions and result from callbacks called by the step
    }
    world->ClearForces ();
}
//FIX TIME STEP<<<<<<<<<<<<<<<<<------------------


-(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/

    // 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);
    [self step:dt];

    //Iterate over the bodies in the physics world
    for (b2Body* b = world->GetBodyList(); b; b = b->GetNext())
    {
        if (b->GetUserData() != NULL) {

            CCSprite *myActor;
            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());

        }
    }
}

Answer 2

当前接受的答案有一些问题......当我尝试它时，在我的快速滚动游戏中，我看到主角的抖动，而摄像机跟随它。我在这里找到了有关此代码的详细信息（为什么这是错误的）http://box2d.org/forum/viewtopic.php?t=5619

所以，我认为更好地使用更强大的插值解决方案：http://plaincode.blogspot.com/2012/05/fixed-timestep-in-cocos2d-x-with-box2d.html

cocos2d没有运行60 FPS WITH FIXED TIMESTEP

2 个答案: