JavaScript利用canvas绘制流星雨效果

//创建一个星星对象
class Star {
  constructor() {
    this.x = windowWidth * Math.random(); //横坐标
    this.y = 5000 * Math.random(); //纵坐标
    this.text = "."; //文本
    this.color = "white"; //颜色
  }
  //初始化
  init() {
    this.getColor();
  }
  //绘制
  draw() {
    context.fillStyle = this.color;
    context.fillText(this.text, this.x, this.y);
  }
}

//画星星
for (let i = 0; i < starCount; i++) {
  let star = new Star();
  star.init();
  star.draw();
  arr.push(star);
}

//创建一个星星对象
class Star {
  constructor() {
    this.x = windowWidth * Math.random(); //横坐标
    this.y = 5000 * Math.random(); //纵坐标
    this.text = "."; //文本
    this.color = "white"; //颜色
  }
	// 获取随机颜色
  getColor() {
    let _r = Math.random();
    if (_r < 0.5) {
      this.color = "#333";
    } else {
      this.color = "white";
    }
  }

  //初始化
  init() {
    this.getColor();
  }
  //绘制
  draw() {
    context.fillStyle = this.color;
    context.fillText(this.text, this.x, this.y);
  }
}

//画星星
for (let i = 0; i < starCount; i++) {
  let star = new Star();
  star.init();
  star.draw();
  arr.push(star);
}

//繁星闪起来
let t1
function playStars() {
  for (let n = 0; n < starCount; n++) {
    arr[n].getColor();
    arr[n].draw();
  }
  t1 = requestAnimationFrame(playStars);
}

  draw() {
    //绘制一个流星的函数
    context.save();
    context.beginPath();
    context.lineWidth = 1; //宽度
    context.globalAlpha = this.alpha; //设置透明度
    //创建横向渐变颜色,起点坐标至终点坐标
    let line = context.createLinearGradient(
      this.x,
      this.y,
      this.x + this.width,
      this.y - this.height
    );
    //分段设置颜色
    line.addColorStop(0, "white");
    line.addColorStop(0.3, this.color1);
    line.addColorStop(0.6, this.color2);
    context.strokeStyle = line;
    //起点
    context.moveTo(this.x, this.y);
    //终点
    context.lineTo(this.x + this.width, this.y - this.height);
    context.closePath();
    context.stroke();
    context.restore();
  }

move() {
    //清空流星像素
    let x = this.x + this.width - this.offset_x;
    let y = this.y - this.height;
    context.clearRect(x - 3, y - 3, this.offset_x + 5, this.offset_y + 5);
    //重新计算位置，往左下移动
    this.countPos();
    //透明度增加
    this.alpha -= 0.002;
    //重绘
    this.draw();
  }

let t2
// 创建流星雨对象
class MeteorRain {
  constructor() {
    this.x = -1;
    this.y = -1;
    this.length = -1; //长度
    this.angle = 30; //倾斜角度
    this.width = -1; //宽度
    this.height = -1; //高度
    this.speed = 1; //速度
    this.offset_x = -1; //横轴移动偏移量
    this.offset_y = -1; //纵轴移动偏移量
    this.alpha = 1; //透明度
    this.color1 = ""; //流星的色彩
    this.color2 = ""; //流星的色彩
  }
  init() {
    //初始化
    this.getPos();
    this.alpha = 1; //透明度
    this.getRandomColor();
    //最小长度，最大长度
    let x = Math.random() * 80 + 150;
    this.length = Math.ceil(x);
    x = Math.random() + 0.5;
    this.speed = Math.ceil(x); //流星的速度
    let cos = Math.cos((this.angle * 3.14) / 180);
    let sin = Math.sin((this.angle * 3.14) / 180);
    this.width = this.length * cos;
    this.height = this.length * sin;
    this.offset_x = this.speed * cos;
    this.offset_y = this.speed * sin;
  }
  
  getRandomColor() {
    let a = Math.ceil(255 - 240 * Math.random());
    //中段颜色
    this.color1 = "rgba(" + a + "," + a + "," + a + ",1)";
    //结束颜色
    this.color2 = "black";
  }
  
  countPos() {
    //
    //往左下移动,x减少，y增加
    this.x = this.x - this.offset_x;
    this.y = this.y + this.offset_y;
  }
  
  getPos() {
    //
    //横坐标
    this.x = Math.random() * window.innerWidth; //窗口高度
    //纵坐标
    this.y = Math.random() * window.innerHeight; //窗口宽度
  }
  
  draw() {
    //绘制一个流星的函数
    context.save();
    context.beginPath();
    context.lineWidth = 1; //宽度
    context.globalAlpha = this.alpha; //设置透明度
    //创建横向渐变颜色,起点坐标至终点坐标
    let line = context.createLinearGradient(
      this.x,
      this.y,
      this.x + this.width,
      this.y - this.height
    );
    //分段设置颜色
    line.addColorStop(0, "white");
    line.addColorStop(0.3, this.color1);
    line.addColorStop(0.6, this.color2);
    context.strokeStyle = line;
    //起点
    context.moveTo(this.x, this.y);
    //终点
    context.lineTo(this.x + this.width, this.y - this.height);
    context.closePath();
    context.stroke();
    context.restore();
  }
  move() {
    //清空流星像素
    let x = this.x + this.width - this.offset_x;
    let y = this.y - this.height;
    context.clearRect(x - 3, y - 3, this.offset_x + 5, this.offset_y + 5);
    //重新计算位置，往左下移动
    this.countPos();
    //透明度增加
    this.alpha -= 0.002;
    //重绘
    this.draw();
  }
}

//绘制流星
function playRains() {
  for (let n = 0; n < rainCount; n++) {
    // console.log(rains, "--");
    let rain = rains[n];
    rain.move(); //移动
    if (rain.y > window.innerHeight) {
      //超出界限后重来
      context.clearRect(rain.x, rain.y - rain.height, rain.width, rain.height);
      rains[n] = new MeteorRain();
      rains[n].init();
    }
  }
  t2 = requestAnimationFrame(playRains);
}