canvas实现雪花随机动态飘落效果

红太狼 2020-06-22 15:28 941阅读 0赞

# canvas实现雪花随机动态飘落效果

![](/images/1592839701255.png)

用canvas实现雪花随机动态飘落，代码如下

```html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  body{
    margin: 0;
    padding: 0;
  }
  canvas{
    background: #000;
  }
</style>
<body>
  <canvas id = "snow">
 
  </canvas>
  <script>
    var canvas = document.getElementById('snow');
    var context = canvas.getContext('2d');
    // 获得可视区的宽高
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight;
    function snow(){
      context.save();
      // 开启路径
      context.beginPath();
      // 移动画布，确定雪花终点为中心点
      context.translate(100,100);
      //起点
      context.moveTo(-20,0);
      // 终点
      context.lineTo(20,0);
      // 线变成白色
      context.strokeStyle = '#fff';
      // 线变粗
      context.lineWidth = 10;
      // 线变圆头
      context.lineCap = 'round';
      context.stroke();
      // 角度转弧度
      var disX = Math.sin(30*Math.PI/180)*20;
      var disY = Math.sin(60*Math.PI/180)*20;
      // 画第二条线，左下到右上的线
      context.moveTo(-disX,disY);
      context.lineTo(disX,-disY);
      // 画第三条线
      context.moveTo(-disX,-disY);
      context.lineTo(disX,disY);
      context.stroke();
      context.restore();
    }
    // snow();
    //生成雪花的构造函数
    function Snow(x,y,scale,rotate,speedX,speedY,speedR){
           this.x = x;
           this.y = y;
           this.scale = scale;
           this.rotate = rotate;
           this.speedX = speedX;
           this.speedY = speedY;
           this.speedR = speedR;
          // 渲染雪花
          this.render = function(){
            context.save();
            context.beginPath();
            context.translate(this.x,this.y);
            context.scale(this.scale,this.scale);
            context.rotate(this.rotate*Math.PI/180);
            context.moveTo(-20,0);
            context.lineTo(20,0);
            context.strokeStyle = '#fff';
            context.lineWidth = 10;
            context.lineCap = 'round';
            context.stroke();
            var disX = Math.sin(30*Math.PI/180)*20;
            var disY = Math.sin(60*Math.PI/180)*20;
            context.moveTo(-disX,disY);
            context.lineTo(disX,-disY);
            context.moveTo(-disX,-disY);
            context.lineTo(disX,disY);
            context.stroke();
            context.restore();
 
          }
 
    }
    // var snow = new Snow(50,50,1,10,10,10,10);
    // snow.render();
    // 存储所有生成的雪花
    var snowArray = [];
    // 生成雪花
      function init(){
        var len = 100;
        for(var i = 0;i<len;i++){
          var x = Math.random()*canvas.width;
          var scale = Math.random()+0.5;
          var rotate = Math.random()*60;
          var speedX = Math.random()+1
          var speedY = Math.random()+5;
          var speedR = Math.random()*4+2;
          // var snow = new Snow(x,0,scale,rotate,speedX,speedY,speedR);
          // snow.render();
          (function(x,y,scale,rotate,speedX,speedY,speedR){
            setTimeout(function(){
            var snow = new Snow(x,0,scale,rotate,speedX,speedY,speedR);
            snow.render();
            snowArray.push(snow);
          },Math.random()*8000);   
          })(x,0,scale,rotate,speedX,speedY,speedR);
      }snowing();
    }init();
      // 动起来
      function snowing(){
        setInterval(function(){
          //先清除
          context.clearRect(0,0,canvas.width,canvas.height);
          for(var i = 0;i < snowArray.length;i++){
            snowArray[i].x = (snowArray[i].x+snowArray[i].speedX)%canvas.width;
            snowArray[i].y = (snowArray[i].y+snowArray[i].speedY)%canvas.height;
            snowArray[i].rotate = (snowArray[i].rotate+snowArray[i].speedR)%60;
            snowArray[i].render();
          }
        },30);
      }
     
    /**
     * sin60 = 对边/斜边 =>  对边 = sin60*斜边  =>  y=sin60*半径（r）；
     */
  </script>
</body>
</html>
```

动态效果图：

![](/images/1592839686362.gif)