用requestAnimationFrame在画布上使用JS倒计时器

Question

我正在制作一个简单的帆布游戏，我使用requestAnimationFrame (保罗爱尔兰版)作为游戏。我在游戏中使用javascript倒计时(显示秒数和100秒)，但它不能以正确的速度计数。我知道这与游戏的刷新率有关，所以计数器更新每帧，而不是每100秒钟更新一次。我该怎么解决这个问题？

以下是计时器对象：

/**
 * The timer as an object
*/
function Timer(position, time) {
  this.position = position || new Vector(150,210);
  this.time = time || 6000;
}

Timer.prototype = {
  start: function() {
    console.log('start running');
    this.initial = this.time; //time in 100'ths of seconds
    this.count = this.initial;
    this.counter; //10 will  run it every 100th of a second
    clearInterval(this.counter);
    //this.counter = setInterval(this.timer, 10);
    this.timer();
  },

  timer: function() {
    //console.log(this.count);
    this.count--;
      var res = this.count / 100;
    //Show counter in canvas
    return 'Tid kvar: ' + res.toPrecision(this.count.toString().length) + ' sekunder';
  },

  draw: function(ct) {
    if(this.initial === undefined){this.start();} //Start the timer
    ct.save();
    if(this.count <=0){ //Remove timer if timer has reached 0
      ct.clearRect(this.position.x, this.position.y, Racetrack.innerTrackWidth, Racetrack.innerTrackHeight);
      return false;
    } else { //draw timer
      ct.save();
      ct.font = 'bold 3em arial';
      ct.fillStyle = 'orange';
      ct.fillText(this.timer(), this.position.x, this.position.y);
    }
    ct.restore();
  }, 
}

游戏和调用计时器的部分：

  var init = function(canvas) {
    timer = new Timer(new Vector(160,210), 3000);
  }

  var render = function() {
    ct.clearRect(0,0,width,height);
    ship.draw(ct);
    racetrack.draw(ct);
    //draw timer or results if timer reached 0
    timer.draw(ct) !=false ? timer.draw(ct) : endFrame.draw(ct);
  };

  var gameLoop = function() {
    var now = Date.now();
    td = (now - (lastGameTick || now)) / 1000; // Timediff since last frame / gametick
    lastGameTick = now;
    if(timer.draw(ct) == false) { //stop the game if timer has reached 0.
      cancelRequestAnimFrame(gameLoop);
      console.log('Time\'s up!');
    } else { //Otherwise, keep the game going.
      requestAnimFrame(gameLoop);
    }
    update(td);
    render();
  };

我也尝试过作为timer- object，但是调试this.count会显示第一个循环的编号，未定义的第二个循环和之后的每个循环(我不确定这会以哪种方式解决定时问题？)：

function Timer(position, time) {
  this.position = position || new Vector(150,210);
  this.time = time || 6000;
}

Timer.prototype = {
  start: function() {
    console.log('start running');
    this.initial = this.time; //time in 100'ths of seconds
    this.count = this.initial;
    this.counter; //10 will  run it every 100th of a second
    clearInterval(this.counter);
    this.counter = setInterval(this.timer, 10);
    this.timer();
  },


  timer: function() {
    console.log(this.count);
    this.count--;
  },

  getTime: function() {
    var res = this.count / 100;
    return 'Tid kvar: ' + res.toPrecision(this.count.toString().length) + ' sekunder';
  },

  draw: function(ct) {
    if(this.initial === undefined){this.start();} //Start the timer
    ct.save();
    if(this.count <=0){ //Remove timer if timer has reached 0
      ct.clearRect(this.position.x, this.position.y, Racetrack.innerTrackWidth, Racetrack.innerTrackHeight);
      return false;
    } else { //draw timer
      ct.save();
      ct.font = 'bold 3em arial';
      ct.fillStyle = 'orange';
      ct.fillText(this.getTime(), this.position.x, this.position.y);
    }
    ct.restore();
  },
}

Answer 1

不确定您是否要求以1/100间隔显示时间，或者使用setInterval时时间是否不准确。

答: setInterval不应该用来计时，因为它不准确，间隔越小，情况就越糟，如果动画运行的话，情况就更糟了。

浏览器的刷新速度是每秒1/60。您可以强制显示以每秒1/100的速度呈现，但根据图形硬件的不同，它可能永远不会显示，因为显示器当时正在扫描屏幕上的其他像素。或者，当您覆盖显示时，就会得到剪切，就像正在将图形写入到显示器上一样。

使用requestAnimationFrame获取倒计时的最佳方法

var start = true;     // flags that you want the countdown to start
var stopIn = 3000;    // how long the timer should run
var stopTime = 0;     // used to hold the stop time
var stop = false;     // flag to indicate that stop time has been reached
var timeTillStop = 0; // holds the display time

// main update function
function update(timer){

    if(start){  // do we need to start the timer
        stopTime = timer + stopIn; // yes the set the stoptime
        start = false;             // clear the start flag
    }else{                         // waiting for stop
        if(timer >= stopTime){     // has stop time been reached?
            stop = true;           // yes the flag to stop
        }
    }

    timeTillStop = stopTime - timer;      // for display of time till stop
    // log() should be whatever you use to display the time.
    log(Math.floor(timeTillStop / 10) );  // to display in 1/100th seconds

    if(!stop){
        requestAnimationFrame(update); // continue animation until stop 
    }
}
requestAnimationFrame(update);  // start the animation

忘了补充了。

通过这种方法，你永远不可能获得100秒的精度。你将平均出7-8毫秒。但是，除非你把它变得更复杂，否则这是你能做的最好的事情。这7-8ms的平均值是恒定的，相同的2小时1秒，只是由动画刷新时间大约16奇毫秒。