javascript - 如何优化大画布动画

Question

我有一个大画布动画，是从 codepen 中获取的。问题是它有时运行有点慢。这就是为什么我想知道如何优化此动画以使其运行更顺畅？我想要尽可能多的提示，如果您可以更改代码中的任何内容来帮助我，我将不胜感激。

$(window).on("load", function() {
    (function() {
      var requestAnimationFrame =
        window.requestAnimationFrame ||
        window.mozRequestAnimationFrame ||
        window.webkitRequestAnimationFrame ||
        window.msRequestAnimationFrame ||
        function(callback) {
          window.setTimeout(callback, 1000 / 60);
        };
      window.requestAnimationFrame = requestAnimationFrame;
    })();

    // Terrain stuff.
    var background = document.getElementById("bgCanvas"),
      bgCtx = background.getContext("2d"),
      width = 1920,
      height = 1080;

    if (height < 400) {
      height = 400;
    }

    background.width = width;
    background.height = height;

    function Terrain(options) {
      options = options || {};
      this.terrain = document.createElement("canvas");
      this.terCtx = this.terrain.getContext("2d");
      this.scrollDelay = options.scrollDelay || 90;
      this.lastScroll = new Date().getTime();

      this.terrain.width = width;
      this.terrain.height = height;
      this.fillStyle = options.fillStyle || "#191D4C";
      this.mHeight = options.mHeight || height;

      // generate
      this.points = [];

      var displacement = options.displacement || 140,
        power = Math.pow(2, Math.ceil(Math.log(width) / Math.log(2)));

      // set the start height and end height for the terrain
      this.points[0] = this.mHeight; //(this.mHeight - (Math.random() * this.mHeight / 2)) - displacement;
      this.points[power] = this.points[0];

      // create the rest of the points
      for (var i = 1; i < power; i *= 2) {
        for (var j = power / i / 2; j < power; j += power / i) {
          this.points[j] =
            (this.points[j - power / i / 2] + this.points[j + power / i / 2]) /
              2 +
            Math.floor(Math.random() * -displacement + displacement);
        }
        displacement *= 0.6;
      }

      document.body.appendChild(this.terrain);
    }

    Terrain.prototype.update = function() {
      // draw the terrain
      this.terCtx.clearRect(0, 0, width, height);
      this.terCtx.fillStyle = this.fillStyle;

      if (new Date().getTime() > this.lastScroll + this.scrollDelay) {
        this.lastScroll = new Date().getTime();
        this.points.push(this.points.shift());
      }

      this.terCtx.beginPath();
      for (var i = 0; i <= width; i++) {
        if (i === 0) {
          this.terCtx.moveTo(0, this.points[0]);
        } else if (this.points[i] !== undefined) {
          this.terCtx.lineTo(i, this.points[i]);
        }
      }

      this.terCtx.lineTo(width, this.terrain.height);
      this.terCtx.lineTo(0, this.terrain.height);
      this.terCtx.lineTo(0, this.points[0]);
      this.terCtx.fill();
    };

    // Second canvas used for the stars
    bgCtx.fillStyle = "#05004c";
    bgCtx.fillRect(0, 0, width, height);

    // stars
    function Star(options) {
      this.size = Math.random() * 2;
      this.speed = Math.random() * 0.05;
      this.x = options.x;
      this.y = options.y;
    }

    Star.prototype.reset = function() {
      this.size = Math.random() * 2;
      this.speed = Math.random() * 0.05;
      this.x = width;
      this.y = Math.random() * height;
    };

    Star.prototype.update = function() {
      this.x -= this.speed;
      if (this.x < 0) {
        this.reset();
      } else {
        bgCtx.fillRect(this.x, this.y, this.size, this.size);
      }
    };

    function ShootingStar() {
      this.reset();
    }

    ShootingStar.prototype.reset = function() {
      this.x = Math.random() * width;
      this.y = 0;
      this.len = Math.random() * 80 + 10;
      this.speed = Math.random() * 10 + 6;
      this.size = Math.random() * 1 + 0.1;
      // this is used so the shooting stars arent constant
      this.waitTime = new Date().getTime() + Math.random() * 3000 + 500;
      this.active = false;
    };

    ShootingStar.prototype.update = function() {
      if (this.active) {
        this.x -= this.speed;
        this.y += this.speed;
        if (this.x < 0 || this.y >= height) {
          this.reset();
        } else {
          bgCtx.lineWidth = this.size;
          bgCtx.beginPath();
          bgCtx.moveTo(this.x, this.y);
          bgCtx.lineTo(this.x + this.len, this.y - this.len);
          bgCtx.stroke();
        }
      } else {
        if (this.waitTime < new Date().getTime()) {
          this.active = true;
        }
      }
    };

    var entities = [];

    // init the stars
    for (var i = 0; i < height; i++) {
      entities.push(
        new Star({
          x: Math.random() * width,
          y: Math.random() * height
        })
      );
    }

    // Add 2 shooting stars that just cycle.
    entities.push(new ShootingStar());
    entities.push(new ShootingStar());
    entities.push(new Terrain({ mHeight: height / 2 - 120 }));
    entities.push(
      new Terrain({
        displacement: 120,
        scrollDelay: 50,
        fillStyle: "rgb(17,20,40)",
        mHeight: height / 2 - 60
      })
    );
    entities.push(
      new Terrain({
        displacement: 100,
        scrollDelay: 20,
        fillStyle: "rgb(10,10,5)",
        mHeight: height / 2
      })
    );

    //animate background
    function animate() {
      bgCtx.fillStyle = "#110E19";
      bgCtx.fillRect(0, 0, width, height);
      bgCtx.fillStyle = "#ffffff";
      bgCtx.strokeStyle = "#ffffff";

      var entLen = entities.length;

      while (entLen--) {
        entities[entLen].update();
      }
      requestAnimationFrame(animate);
    }
    animate();
  });

编辑：当我说慢时，我的意思是动画断断续续且不流畅

标签： javascripthtmlcsscanvas

Answer 1

我很确定这是你的Terrain#update。特别是你的循环

    Terrain.prototype.update = function() {
      for (var i = 0; i <= width; i++) {
        if (i === 0) {
          this.terCtx.moveTo(0, this.points[0]);
        } else if (this.points[i] !== undefined) {
          this.terCtx.lineTo(i, this.points[i]);
        }
      }

你有width = 1920，所以每个update循环将循环 1920 次，每秒 60 个循环，用于 3 个元素。1920 * 60 * 3 = 每秒约 230,000 次迭代。尝试增加for循环中的间隔，看看是否有帮助

for (var i = 0; i <= width; i += 3) { // or maybe an even higher interval

编辑：再看一点之后，您似乎也在Star屏幕上绘制了 1000 个对象。您可能需要考虑降低该数字。你会用这个让每个人的电脑着火！