FPS

本节件数如何构造一个计算 FPS 的类

类声明

    class FramesPerSecondCounter
    {
    public:
        explicit FramesPerSecondCounter(float avgInterval = 0.5f)
        :avgInterval_(avgInterval)
        {
            assert(avgInterval > 0.0f);
        }

        bool tick(float deltaSeconds, bool frameRendered = true)
        {
            if (frameRendered)
                numFrames_++;

            accumulatedTime_ += deltaSeconds;

            if (accumulatedTime_ > avgInterval_)
            {
                currentFPS_ = static_cast<float>(numFrames_ / accumulatedTime_);
                if (printFPS_)
                    printf("FPS: %.1f\n", currentFPS_);
                numFrames_ = 0;
                accumulatedTime_ = 0;
                return true;
            }

            return false;
        }

        inline float getFPS() const { return currentFPS_; }

        bool printFPS_ = true;

    private:
        const float avgInterval_ = 0.5f;
        unsigned int numFrames_ = 0;
        double accumulatedTime_ = 0;
        float currentFPS_ = 0.0f;
    };

这里主要说明下几个私有属性的意义：
1. avgInterval_，统计时间窗口，默认 0.5s 统计一次；
2. numFrames_，统计窗口内，当前绘制了多少帧；
3. accumulatedTime_，统计窗口内，当前已经过了多少时间；
4. currentFPS_，计算出来的 FPS 是多少；

对于 tick 方法，主要是：
1. 累加 numFrames_ 窗口内的渲染帧数；
2. 累加 accumulatedTime_ 窗口渲染的时间；
3. 如果 accumulatedTime_ 超过了窗口的大小，则计算 FPS，并更新 currentFPS_，同时重置 numFrames_、accumulatedTime_，进入下一次计算周期；

如何使用

1. 声明好当前时间、时间间隔和 FPS 类

    double timeStamp = glfwGetTime();
    float deltaSeconds = 0.0f;
   
    FramesPerSecondCounter fpsCounter(0.5f);
   

2. 在主循环中，更新时间间隔，并调用 tick 方法

    while (!glfwWindowShouldClose(window))
    {
        fpsCounter.tick(deltaSeconds);
   
        positioner.update(deltaSeconds, mouseState.pos, mouseState.pressedLeft);
   
        const double newTimeStamp = glfwGetTime();
        deltaSeconds = static_cast<float>(newTimeStamp - timeStamp);
        timeStamp = newTimeStamp;