加速度计和精灵面部方向

Question

我正在制作一个简单的游戏，我的精灵通过使用加速度计来移动。我的精灵是一个眼睛盯着它的圆圈。我想以一种始终面向它移动方向的方式旋转精灵。下面的代码使用加速度计成功移动精灵但是我无法旋转精灵以面向移动方向。

-(void) moveHeroFromAccelaration
{
    GLKVector3 raw = GLKVector3Make(_motionManager.accelerometerData.acceleration.x,_motionManager.accelerometerData.acceleration.y,_motionManager.accelerometerData.acceleration.z);

    if(GLKVector3AllEqualToScalar(raw, 0))
        return;

    static GLKVector3 ax, ay, az;
    ay = GLKVector3Make(0.63f, 0.0f, -0.92f);
    az = GLKVector3Make(0.0f, 1.0f, 0.0f);
    ax = GLKVector3Normalize(GLKVector3CrossProduct(az, ay));

    CGPoint accel2D = CGPointZero;
    accel2D.x = GLKVector3DotProduct(raw, az); accel2D.y = GLKVector3DotProduct(raw, ax);
    accel2D = CGPointNormalize(accel2D);

    static const float steerDeadZone = 0.18;
    if (fabsf(accel2D.x) < steerDeadZone) accel2D.x = 0; if (fabsf(accel2D.y) < steerDeadZone) accel2D.y = 0;

    float maxAccelerationPerSecond = 160.0f;
    _hero.physicsBody.velocity =
    CGVectorMake(accel2D.x * maxAccelerationPerSecond, accel2D.y * maxAccelerationPerSecond);

    //1
    if (accel2D.x!=0 || accel2D.y!=0) {
        //2
        float orientationFromVelocity = CGPointToAngle(CGPointMake(_hero.physicsBody.velocity.dx,
                                                                   _hero.physicsBody.velocity.dy));

        float angleDelta = 0.0f;
        //3
        if (fabsf(orientationFromVelocity-_hero.zRotation)>1) { //prevent wild rotation
            angleDelta = (orientationFromVelocity-_hero.zRotation);
        } else {
            //blend rotation
            const float blendFactor = 0.25f; angleDelta =
            (orientationFromVelocity - _hero.zRotation) * blendFactor; angleDelta =
            ScalarShortestAngleBetween(_hero.zRotation, _hero.zRotation + angleDelta);
        }
        _hero.zRotation += angleDelta;


        // face the hero in the moving direction 
        [_hero runAction:[SKAction rotateToAngle:orientationFromVelocity duration:0.25 shortestUnitArc:YES]]; <---- THIS IS WHERE I NEED HELP! 

    }

}