canvas怎么画特效（canvas中普通动效与粒子动效的实现代码示例）

  // 小时时间刻度
  offscreenCanvasCtx.save();
  for (var i = 0; i < 12; i++) {
    offscreenCanvasCtx.beginPath();
    // 刻度颜色
    offscreenCanvasCtx.strokeStyle = '#fff';
    // 刻度宽度
    offscreenCanvasCtx.lineWidth = 3;
    // 每小时占据30°
    offscreenCanvasCtx.rotate(Math.PI / 6);
    // 开始绘制的位置
    offscreenCanvasCtx.lineTo(140, 0)
    // 结束绘制的位置;
    offscreenCanvasCtx.lineTo(120, 0);
    // 绘制路径
    offscreenCanvasCtx.stroke();
  }
  offscreenCanvasCtx.restore();

  var now = new Date(),
    sec = now.getSeconds(),
    min = now.getMinutes(),
    hr = now.getHours();
  hr = hr > 12 ? hr - 12 : hr;
  
  //秒针
  offscreenCanvasCtx.save();
  offscreenCanvasCtx.rotate(sec * (Math.PI / 30));
  ......
  offscreenCanvasCtx.stroke();

let image = new Image();
  image.src='../image/logo.jpg" alt="canvas怎么画特效（canvas中普通动效与粒子动效的实现代码示例）" border="0" />

 function getPixels(){
    var pos=0;
    var data=imageData.data; //RGBA的一维数组数据
    //源图像的高度和宽度为300px
    for(var i=1;i<=image.width;i++){
      for(var j=1;j<=image.height;j++){
        pos=[(i-1)*image.width+(j-1)]*4; //取得像素位置
        if(data[pos]>=0){
          var pixel={
            x:(canvas.width-image.width)/2+j+Math.random()*20, //重新设置每个像素的位置信息
            y:(canvas.height-image.height)/2+i+Math.random()*20, //重新设置每个像素的位置信息
            fillStyle:'rgba('+data[pos]+','+(data[pos+1])+','+(data[pos+2])+','+(data[pos+3])+')'
          }
          pixels.push(pixel);
        }
      }
    }
  }
  function drawPixels() {
    var canvas = document.getElementById("myCanvas");
    var ctx = canvas.getContext("2d");
    ctx.clearRect(0,0,canvas.width,canvas.height);
    var len = pixels.length, curr_pixel = null;
    for (var i = 0; i < len; i++) {
      curr_pixel = pixels[i];
      ctx.fillStyle = curr_pixel.fillStyle;
      ctx.fillRect(curr_pixel.x, curr_pixel.y, 1, 1);
    }
  }

 function time() {
    ctx.clearRect(0,0,canvas.width,canvas.height)
    ctx.font = "150px 黑体";
    ctx.textBaseline='top';
    ctx.fillStyle = "rgba(245,245,245,0.2)";
    ctx.fillText(new Date().format('hh:mm:ss'),(canvas.width-textWidth)/2,(canvas.height-textHeight)/2,textWidth,textHeight);
  }

  function getPixels(){
    let imgData = ctx.getImageData((canvas.width-textWidth)/2,(canvas.height-textHeight)/2,textWidth,textHeight);
    let data = imgData.data
    pixelsArr = []
    for(let i=1;i<=textHeight;i++){
      for(let j=1;j<=textWidth;j++){
        pos=[(i-1)*textWidth+(j-1)]*4; //取得像素位置
        if(data[pos]>=0){
          var pixel={
            x:j+Math.random()*20, //重新设置每个像素的位置信息
            y:i+Math.random()*20, //重新设置每个像素的位置信息
            fillStyle:'rgba('+data[pos]+','+(data[pos+1])+','+(data[pos+2])+','+(data[pos+3])+')'
          };
          pixelsArr.push(pixel);
        }
      }
    }
  }

  function drawPixels() {
    // 清除画布内容，进行重绘
    ctx.clearRect(0,0,canvas.width,canvas.height);
    for (let i in pixelsArr) {
      ctx.fillStyle = pixelsArr[i].fillStyle;
      let r = Math.random()*4
      ctx.fillRect(pixelsArr[i].x, pixelsArr[i].y, r, r);
    }
  }

  function time() {
    ......
    getpixels(); //获取粒子
    drawPixels(); // 重绘粒子
    requestAnimationFrame(time);
  }