使基于画布滚动的图像序列动画更流畅

Question

我想要一个带有如下图像序列的基于滚动的动画：

http://www.clearmotion.com/technology

这个动画看起来很流畅

我试过这个小提琴

var images = new Array();
var currentLocation = 0;
var totalImages = 200;

for (var i = 1; i < totalImages; i++) {
    var img = new Image;
   
    var slug = '000' + i;
    
     img.src = 'https://s3.amazonaws.com/clearmotion/hero/high-min/frame'+ slug.slice(-3) +'-low.jpg'
    images.push(img);
}

var c = document.getElementById("background");
var ctx = c.getContext("2d");

var mouseWheel = function () {
    window.addEventListener('mousewheel', function (e) {
        e.preventDefault(); // No scroll

        // The following equation will return either a 1 for scroll down
        // or -1 for a scroll up
        var delta = Math.max(-1, Math.min(1, e.wheelDelta));

        // This code mostly keeps us from going too far in either direction
        if (delta == -1) currentLocation += 1;
        if (delta == 1) currentLocation -= 1;
        if (currentLocation < 0) currentLocation = 0;
        if (currentLocation >= (totalImages - 1)) currentLocation = (totalImages - 1);
        console.log("Current location " + currentLocation);

        // See below for the details of this function
        setImage(currentLocation);
    });
}

var setImage = function (newLocation) {
    // drawImage takes 5 arguments: image, x, y, width, height
    ctx.fillRect(0, 0, c.width, c.height);
    ctx.drawImage(images[newLocation], 0, 0, 1000, 1000);
}

images[0].onload = function () {
    ctx.fillRect(0, 0, c.width, c.height);
    ctx.drawImage(images[currentLocation], 0, 0, 1000, 1000);
    mouseWheel();
};

  <canvas id="background" width="1000" height="1000"></canvas>

`

然而，效果看起来很糟糕。

当我的鼠标停止滚动时，动画立即停止

我怎样才能让它更平滑？

Answer 1

发生这种情况是因为滚轮事件可能以非常高的速率触发，高于屏幕刷新率。
这意味着对于绘制到屏幕上的每一帧，您实际上在画布上绘制了几个帧。然后，浏览器在处理所有这些请求时会遇到一些问题，并最终造成延迟。

为了避免这种情况，您可以限制您的事件：有条件地执行您的回调，仅当它已经超过某个预定义时间时才尚未触发。

在处理视觉动画时，这种节流时间的良好基础是屏幕刷新。我们有一个计时方法可以做到这一点：requestAnimationFrame。

var images = new Array();
var currentLocation = 0;
var totalImages = 200;

for (var i = 1; i < totalImages; i++) {
  var img = new Image;
  var slug = '000' + i;
  img.src = 'https://s3.amazonaws.com/clearmotion/hero/high-min/frame' + slug.slice(-3) + '-low.jpg'
  images.push(img);
}

var c = document.getElementById("background");
var ctx = c.getContext("2d");

var mouseWheel = function() {
  var evt = null; // avoids a new 'draw' function generation
  window.addEventListener('wheel', function(e) {
    e.preventDefault(); // No scroll

    if (!evt) { // if set, we already are waiting
      evt = e; // store our event
      requestAnimationFrame(draw); // wait next screen refresh to fire
    }
  });
  // the throttled funtion
  function draw() {
    var e = evt;
    var delta = Math.max(-1, Math.min(1, e.deltaY));
    if (delta == -1) currentLocation += 1;
    if (delta == 1) currentLocation -= 1;
    if (currentLocation < 0) currentLocation = 0;
    if (currentLocation >= (totalImages - 1)) currentLocation = (totalImages - 1);
    setImage(currentLocation);
    evt = null; // so the throttler knows we can kick again
  }
}

var setImage = function(newLocation) {
  if (!images[newLocation]) return;
  ctx.fillRect(0, 0, c.width, c.height);
  ctx.drawImage(images[newLocation], 0, 0, 1000, 1000);
}

images[0].onload = function() {
  ctx.fillRect(0, 0, c.width, c.height);
  ctx.drawImage(images[currentLocation], 0, 0, 1000, 1000);
  mouseWheel();
};

<canvas id="background" width="1000" height="1000"></canvas>

现在，由于我们阻止了整个事件处理，因此您的动画也可能看起来更慢（即使更流畅）。为了避免这种情况，您仍然可以尽可能快地更新变量，并且仅限制实际绘图。

var images = new Array();
var currentLocation = 0;
var totalImages = 200;

for (var i = 1; i < totalImages; i++) {
  var img = new Image;
  var slug = '000' + i;
  img.src = 'https://s3.amazonaws.com/clearmotion/hero/high-min/frame' + slug.slice(-3) + '-low.jpg'
  images.push(img);
}

var c = document.getElementById("background");
var ctx = c.getContext("2d");

var mouseWheel = function() {
  var newLocation = null;
  window.addEventListener('wheel', function(e) {
    e.preventDefault(); // No scroll

    // update our variable at high frequency
    var delta = Math.max(-1, Math.min(1, e.deltaY));
    if (delta == -1) currentLocation += 1;
    if (delta == 1) currentLocation -= 1;
    if (currentLocation < 0) currentLocation = 0;
    if (currentLocation >= (totalImages - 1)) currentLocation = (totalImages - 1);

    if (newLocation === null) { // if set, we already are waiting to draw
      requestAnimationFrame(setImage);
    }
    newLocation = currentLocation;
  });

  function setImage() {
    if (images[newLocation]) {
      ctx.fillRect(0, 0, c.width, c.height);
      ctx.drawImage(images[newLocation], 0, 0, 1000, 1000);
    }
    newLocation = null; // so the throttler knows we can draw again
  }

}


images[0].onload = function() {
  ctx.fillRect(0, 0, c.width, c.height);
  ctx.drawImage(images[currentLocation], 0, 0, 1000, 1000);
  mouseWheel();
};

<canvas id="background" width="1000" height="1000"></canvas>

请注意，我确实更新了您的活动以使用唯一符合规范的活动：WheelEvent。
另请注意，您可能最好加载视频而不是加载那么多静态图像。或者甚至将原始 3D 动画转换为 webGL。