计算目标物体的活跃度()
{
    // ==== 第一阶段 ==== 

    获取目标物体与热点(摄像机或玩家的位置)的距离

    分别计算四种内建 FOI 在不同权重下的影响度，并累加

    分别计算所有用户添加的 FOI 在不同权重下的影响度，并累加

    计算经过所有 FOI 修正过的距离

    // ==== 第二阶段 ==== 

    使用当前系统的性能评级和 FPS 来修正活跃度区域的上下限（也即热力环的热力衰减运算）

    // ==== 第三阶段 ==== 

    使用上面两个阶段的计算结果得出该物体的活跃度 
}

    private void _updateLiveness(IMetaLodTarget target)

public class UMetaLodConst 
{
    // the bounding volume of the target
    public const string Factor_Bounds = "Bounds";

    // currently corresponds to vertex count of the target mesh, would be 0 for particle system
    public const string Factor_GeomComplexity = "GeomComplexity";

    // currently correspends to particle count of the target particle system, would be 0 for ordinary mesh
    public const string Factor_PSysComplexity = "PSysComplexity";  

    // a subjective factor which reveals the visual importance of the target in some degrees
    // for instance, skill effects casted by player would generally has a 
    // pretty much higher visual impact than a static stone on the ground
    public const string Factor_VisualImpact = "VisualImpact";
}

public delegate float fnFactorNormalize(float value, float upper, float lower);

...

public struct UImpactFactor
{
    ...

    // customized Normalizer for different Impact Factor 
    public fnFactorNormalize Normalizer;
}

...

// use methods like InverseLerp() to transform the parameter value into a valid FOI 
Normalizer = (value, upper, lower) => { return UMetaLodUtil.Percent(lower, upper, value); }

public static class UMetaLodConfig
{
    // the time interval of an update (could be done discretedly)
    public static float UpdateInterval = 0.5f;

    // the time interval of an FPS update (could be done discretedly)
    public static float FPSUpdateInterval = 5.0f;

    // debug option (would output debugging strings to lod target if enabled)
    public static bool EnableDebuggingOutput = false;

    // performance level (target platform horsepower indication)
    public static UPerfLevel PerformanceLevel = UPerfLevel.Medium;
    // performance level magnifier
    public static Dictionary<UPerfLevel, float> PerfLevelScaleLut = new Dictionary<UPerfLevel, float> 
    {
        { UPerfLevel.Highend, 0.2f },
        { UPerfLevel.Medium, 0.0f },
        { UPerfLevel.Lowend, -0.2f },
    };

    // heat attenuation parameters overriding (including the formula)
    public static float DistInnerBound = 80.0f;
    public static float DistOuterBound = 180.0f;
    public static float FpsLowerBound = 15.0f;
    public static float FpsStandard = 30.0f;
    public static float FpsUpperBound = 60.0f;
    public static float FpsMinifyFactor = -0.2f;
    public static float FpsMagnifyFactor = 0.2f;
    public static fnHeatAttenuate HeatAttenuationFormula = UMetaLodDefaults.HeatAttenuation;
}