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canvas scratch effect_html/css_WEB-ITnose
- WBOYOriginal
- 2016-06-24 11:44:551137browse
The last time I wrote about the scratch-off effect was a year ago. At that time, I found the source code from Baidu and modified it. I was actually confused. This time, I asked a girl to write it, and then I thought Reorganize it yourself.
<!DOCTYPE html><html><head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0"> <title>刮奖效果</title> <style type="text/css"> #canvas{ display: block; margin:0 auto; } </style></head><body> <canvas id="canvas"></canvas> <script type="text/javascript"> // 初始化，设置canva的宽(width)、高(height),涂抹画笔的直径(r)，背景图片(img)（即底层的图片）,上层遮罩层 var width=440; var height=440; var r=20; var img = new Image(); img.src="1.jpg"; var canvas=document.getElementById("canvas"); canvas.style.backgroundImage='url('+img.src+')'; canvas.width=width; canvas.height=height; var ctx=canvas.getContext("2d"); ctx.fillStyle="#ccc"; ctx.fillRect(0,0,width,height); //绘制上层的涂层 ctx.globalCompositeOperation="destination-out"; //在源图像外显示目标图像。只有源图像外的目标图像部分会被显示，源图像是透明的。 var isMove=false; var el=new Array(); el.x=canvas.offsetLeft; el.y=canvas.offsetTop; /************************************ 方式一：利用arc来模拟两端圆角的直线 ***********************************/ //按下时 function touchStart(e){ e.preventDefault(); isMove=true; ctx.closePath(); } // 移动时 function touchMove(e){ e.preventDefault(); var x,y; if(isMove){ if(e.targetTouches){ //移动端 var touch=e.targetTouches[0]; x=touch.clientX-el.x; //坐标矫正 y=touch.clientY-el.y; }else{ //pc端 x=e.pageX-el.x; y=e.pageY-el.y; } ctx.beginPath(); ctx.arc(x,y,r,0,Math.PI*2); //绘制笔触 ctx.fill(); ctx.closePath(); //每次闭合路径 } } // 离开时 function touchEnd(e){ e.preventDefault(); isMove=false ; ctx.closePath(); //涂抹区域百分比 var imgData=ctx.getImageData(0,0,width,height);//返回ImageData对象，该对象拷贝画布指定的像素数据 var pixles=imgData.data; var transNum=0; //rgba以数组形式储存在imageData中， // r=imgData.data[0]; // g=imgData.data[1]; // b=imgData.data[2]; // a=imgData.data[3]; for(var i=3,j=pixles.length;i<j;i+=4){ var a=pixles[i]; if(a==0){ transNum++ } } var transPercent=transNum/(pixles.length/4);//透明度比 console.log(transPercent); //超过某个值显示所有 if(transPercent>0.5){ ctx.fillRect(0,0,width,height); } } /************************************************************************** 方式二：ctx.lineTo(x,y)来画直线，用ctx.lineCap="round";来设置直线两端的圆角 当滑的很快的时候，这种效果比第一种好 ***************************************************************************/ //按下时 // function touchStart(e){ // e.preventDefault(); // isMove=true; // var x,y; // if(e.targetTouches){ //移动端 // var touch=e.targetTouches[0]; // x=touch.clientX-el.x; // y=touch.clientY-el.y; // }else{ //pc端 // x=touch.clientX-el.x; // y=touch.clientY-el.y; // } // ctx.beginPath(); // ctx.lineCap="round"; // ctx.lineJoin="round"; // ctx.lineWidth=r; // ctx.moveTo(x,y); // } // // 移动时 // function touchMove(e){ // e.preventDefault(); // var x,y; // if(isMove){ // if(e.targetTouches){ //移动端 // var touch=e.targetTouches[0]; // x=touch.clientX; // y=touch.clientY; // }else{ //pc端 // x=e.pageX; // y=e.pageY; // } // ctx.lineTo(x,y); //绘制笔触 // ctx.stroke(); // } // } // // 离开时 // function touchEnd(e){ // e.preventDefault(); // isMove=false ; // ctx.closePath(); // } // 事件监听 canvas.addEventListener("touchstart",touchStart); canvas.addEventListener("mousedown",touchStart); canvas.addEventListener("touchmove",touchMove); canvas.addEventListener("mousemove",touchMove); canvas.addEventListener("touchend",touchEnd); canvas.addEventListener("mouseup",touchEnd); </script></body></html>
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