案例效果 | canvas刮刮卡抽奖

HTML5学堂

发布于 2021-11-25 02:13:41

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代码可运行

案例效果

案例代码

HTML代码

<!DOCTYPE html>
<html lang="zh">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>刮刮卡抽奖 - 公众号：HTML5 WEB前端分享</title>
  <link rel="stylesheet" type="text/css" href="http://css.h5course.cn/reset-1.0.0.css">
    <script type="text/javascript">
    !function(N,M){function L(){var a=I.getBoundingClientRect().width;a/F>540&&(a=540*F);var d=a/10;I.style.fontSize=d+"px",D.rem=N.rem=d}var K,J=N.document,I=J.documentElement,H=J.querySelector('meta[name="viewport"]'),G=J.querySelector('meta[name="flexible"]'),F=0,E=0,D=M.flexible||(M.flexible={});if(H){console.warn("将根据已有的meta标签来设置缩放比例");var C=H.getAttribute("content").match(/initial\-scale=([\d\.]+)/);C&&(E=parseFloat(C[1]),F=parseInt(1/E))}else{if(G){var B=G.getAttribute("content");if(B){var A=B.match(/initial\-dpr=([\d\.]+)/),z=B.match(/maximum\-dpr=([\d\.]+)/);A&&(F=parseFloat(A[1]),E=parseFloat((1/F).toFixed(2))),z&&(F=parseFloat(z[1]),E=parseFloat((1/F).toFixed(2)))}}}if(!F&&!E){var y=N.navigator.userAgent,x=(!!y.match(/android/gi),!!y.match(/iphone/gi)),w=x&&!!y.match(/OS 9_3/),v=N.devicePixelRatio;F=x&&!w?v>=3&&(!F||F>=3)?3:v>=2&&(!F||F>=2)?2:1:1,E=1/F}if(I.setAttribute("data-dpr",F),!H){if(H=J.createElement("meta"),H.setAttribute("name","viewport"),H.setAttribute("content","initial-scale="+E+", maximum-scale="+E+", minimum-scale="+E+", user-scalable=no"),I.firstElementChild){I.firstElementChild.appendChild(H)}else{var u=J.createElement("div");u.appendChild(H),J.write(u.innerHTML)}}N.addEventListener("resize",function(){clearTimeout(K),K=setTimeout(L,300)},!1),N.addEventListener("pageshow",function(b){b.persisted&&(clearTimeout(K),K=setTimeout(L,300))},!1),"complete"===J.readyState?J.body.style.fontSize=12*F+"px":J.addEventListener("DOMContentLoaded",function(){J.body.style.fontSize=12*F+"px"},!1),L(),D.dpr=N.dpr=F,D.refreshRem=L,D.rem2px=function(d){var c=parseFloat(d)*this.rem;return"string"==typeof d&&d.match(/rem$/)&&(c+="px"),c},D.px2rem=function(d){var c=parseFloat(d)/this.rem;return"string"==typeof d&&d.match(/px$/)&&(c+="rem"),c}}(window,window.lib||(window.lib={}));
</script>
  <style>
    .wrap {
      padding: 10rem 0 0;
    }
    .canvas-main {
      width: 8.933333rem;
      height: 3.466666rem;
      margin: 0 auto;
      background: url(images/bg.png) center center no-repeat;
      background-size: 100%;
    }
    .wrap canvas {
      width: 8.933333rem;
      height: 3.466666rem;
    }
</style>
</head>
<body>
    <!-- 公众号：HTML5 WEB前端分享 -->
    <!-- 作者：梦幻雪冰（懂点君） -->
  <div class="wrap" id="outer">
    <div class="canvas-main">
      <canvas id="scrape-canvas"></canvas>      
    </div>
  </div>
  <script src="http://js.h5course.cn/jquery-1.11.3.min.js"></script>
  <script src="js/index.js"></script>
</body>
</html>

JavaScript代码

/**
 * 公众号：HTML5 WEB前端分享
 * 作者：梦幻雪冰（懂点君）
 */
// 显示设备的物理像素分辨率与CSS像素分辨率之比
var ratio = window.devicePixelRatio || 1,
fontem = parseInt(window.getComputedStyle(document.documentElement, null)["font-size"]),
canvas = document.getElementById('scrape-canvas'),
width = canvas.clientWidth * ratio,
height = canvas.clientHeight * ratio,
context = canvas.getContext("2d");
canvas.width = width;
canvas.height = height;

// 绘制目标图像
context.fillStyle = '#aaa';
context.fillRect(0, 0, width, height);
context.fill();
context.font = "2rem Arial";
// 水平对齐
context.textAlign = "center";
// 垂直对齐
context.textBaseline = "middle";
context.fillStyle = "#666";
context.fillText("刮奖区", width / 2, height / 2 + 6);

// 新绘制和已经存在的canvas内容不重叠的部分的canvas内容会被保留，重叠的会透明掉
context.globalCompositeOperation = 'destination-out';

//PC端的处理
canvas.addEventListener("mousedown", handlerDownFn, false);
canvas.addEventListener("mousemove", handlerMoveFn, false);
canvas.addEventListener("mouseup", handlerUpFn, false);
//移动端的处理
canvas.addEventListener('touchstart', handlerDownFn, false);
canvas.addEventListener('touchmove', handlerMoveFn, false);
canvas.addEventListener('touchend', handlerUpFn, false);

var hasDown = false;

// 鼠标按下
function handlerDownFn(event) {
  event.preventDefault();
  hasDown = true;
}

// 鼠标移动
function handlerMoveFn(event) {
  event.preventDefault();
  
  if (hasDown) {
    if (event.changedTouches) {
      // changedTouches：涉及当前(引发)事件的触摸点的列表
      event = event.changedTouches[event.changedTouches.length - 1];
    }
    
    var scrollTop = document.documentElement.scrollTop || document.body.scrollTop,
    x = event.clientX - canvas.offsetLeft,
    y = scrollTop + event.clientY - canvas.offsetTop;

    context.beginPath();
    context.arc(x * ratio - fontem / 2, y * ratio - fontem / 2, fontem * 1, 0, Math.PI * 2, true);
    //设置globalCompositeOperation = 'destination-out'，画出来是透明的
    context.fill();
  }
}

// 鼠标抬起
function handlerUpFn(event) {
  event.preventDefault();

  //得到canvas的全部数据
  var imageData = context.getImageData(0, 0, width, height),
  length = imageData.data.length,
  transparentCount = 0;
  
  for (var i = 3; i < length; i += 4) {
    // 判断alpha值是否为0，0为透明
    if (imageData.data[i] == 0) transparentCount++;
  }
  
  //当被刮开的区域等于四分之一时，则可以开始处理结果
  if (transparentCount >= (length / 4 / 4)) {
    alert('刮开啦');
  }
  
  hasDown = false;
}