mr-crocs-adventures/js/FrameRateMeasurer.js

import FrameRateMeasuredEvent from "./events/FrameRateMeasuredEvent.js";

export default class FrameRateMeasurer
{
    constructor(rounds = 30)
    {
        this.rounds = rounds;
        this.round = 0;
        this.lastTimestamp = undefined;
        this.frameDurations = [];

        window.requestAnimationFrame(
            (timestamp) => {
                this.measureFrameRate(timestamp);
            }
        );
    }

    measureFrameRate(timestamp)
    {
        if (this.lastTimestamp !== undefined) {
            this.round++;
            this.frameDurations.push(timestamp - this.lastTimestamp);

            this.lastTimestamp = timestamp;

            if (this.round < this.rounds) {
                window.requestAnimationFrame(
                    (timestamp) => {
                        this.measureFrameRate(timestamp);
                    }
                );
            } else {
                window.dispatchEvent(new FrameRateMeasuredEvent(this.getAverageFrameRate()));
            }
        } else {
            this.round = 0;
            this.lastTimestamp = timestamp;
            window.requestAnimationFrame(
                (timestamp) => {
                    this.measureFrameRate(timestamp);
                }
            );
        }

        this.lastTimestamp = timestamp
    }

    getAverageFrameRate()
    {
        let frameDurationSum = 0;

        this.frameDurations.forEach(
            (duration) => {
                frameDurationSum += duration;
            }
        );

        let durationAverage = frameDurationSum / this.frameDurations.length;

        return 1000 / durationAverage;
    }

    getFrameRate()
    {
        const DEFAULT_FRAME_RATES = [30, 60, 120];

        let averageFrameRate = this.getAverageFrameRate();
        let closestDistance = {frameRate: 0, distance: 99999};

        DEFAULT_FRAME_RATES.forEach(
            (frameRate) => {
                let distance = Math.abs(frameRate - averageFrameRate);

                if (closestDistance.distance > distance) {
                    closestDistance.frameRate = frameRate;
                    closestDistance.distance = distance;
                }
            }
        );

        return closestDistance.frameRate;
    }
}