canvas跟随鼠标画有透明度的矩形边框

提示：canvas跟随鼠标画有透明度的矩形边框

文章目录

前言
一、跟随鼠标画有透明度的矩形边框
总结

前言

一、跟随鼠标画有透明度的矩形边框

test.html

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>canvas跟随鼠标移动画透明线</title><style>div,canvas,img{user-select: none;}.my_canvas,.bg_img{position: absolute;top: 50%;left: 50%;transform: translate(-50%,-50%);}.cf{content: '';display: block;overflow: hidden;clear: both;}.fl{float: left;}.fr{float: right;}.bg_img{width: 674px;height: 495px;background: #ddd;}.img_tools{position: absolute;top: 20px;left: 50%;transform: translateX(-50%);border: 1px solid #eee;border-radius: 64px;height: 64px;line-height: 64px;box-sizing: border-box;padding: 15px 20px 0;}.img_tool{height: 32px;line-height: 32px;color: #000;font-size: 14px;text-align: center;width: 80px;border: 1px solid #ddd;border-radius: 32px;margin-right: 10px;cursor: pointer;}.img_tool_active{color: #409EFF;border: 1px solid #409EFF;}</style>
</head>
<body><div class="bg_img"></div><canvas id="myCanvasBot" class="my_canvas" width="674" height="495"></canvas><canvas id="myCanvasTop" class="my_canvas" width="674" height="495"></canvas><div class="img_tools cf"><div class="img_tool img_tool_active fl" onclick="changeType('curve',this)">涂鸦</div><div class="img_tool fl" onclick="changeType('line',this)">直线</div><div class="img_tool fl" onclick="changeType('rect',this)">矩形</div><div class="img_tool fl" onclick="changeType('eraser',this)">橡皮擦</div></div><script>const canvasWidth = 674;const canvasHeight = 495;//底层canvasconst botCan = document.getElementById('myCanvasBot');//顶层canvasconst topCan = document.getElementById('myCanvasTop');//底层画布const botCtx = botCan.getContext('2d');//顶层画布const topCtx = topCan.getContext('2d');topCtx.lineCap = 'round';topCtx.lineJoin = 'round';//鼠标是否按下  是否移动let isDown = false,isMove = false;//鼠标是否在canvas上抬起let isCanUp = false;//需要画图的轨迹let drawPoints = [];//起始点x,ylet startPoint = {x:0,y:0};//图片历史let imgHistory = [];//icon历史// let partHistory = [];//操作类型let drawType = 'curve';//画线宽度const lineWidth = 10;//鼠标按下const mousedown = (e)=>{isDown = true;let x = (e||window.event).offsetX;let y = (e||window.event).offsetY;startPoint = {x,y};drawPoints.push([{x,y}]);topCtx.strokeStyle = 'rgba(255,0,0,0.2)';topCtx.lineWidth = lineWidth;topCtx.beginPath();topCtx.moveTo(x,y);}//鼠标移动const mousemove = (e)=>{let x = (e||window.event).offsetX;let y = (e||window.event).offsetY;if(isDown){isMove = true;switch(drawType){case 'curve':drawCurve(x,y);break;case 'line':drawLine(x,y);break;case 'eraser':drawEraser(x,y);break;case 'rect':drawRect(x,y);break;}}}//鼠标抬起const mouseup = (e)=>{isCanUp = true;if(isDown){// topCan内容画到botCan上topToBot();}}//topCan内容画到botCan上const topToBot = ()=>{//把topCan画布生成图片let img = new Image();img.src = topCan.toDataURL('image/png');img.onload = ()=>{// partHistory.push(img);//添加到botCtx画布botCtx.drawImage(img,0,0);let historyImg = new Image();historyImg = botCan.toDataURL('image/png');historyImg.onload = ()=>{//添加到历史记录imgHistory.push(historyImg);}//清除topCtx画布topCtx.clearRect(0,0,canvasWidth,canvasHeight);//botCan画完之后，重置canvas的mouseup isCanUpif(isCanUp)isCanUp=false;}drawPoints = [];isDown = false;isMove = false;}//画矩形const drawRect = (x,y)=>{//清除topCtx画布topCtx.clearRect(0,0,canvasWidth,canvasHeight);topCtx.beginPath();// 矩形topCtx.rect(startPoint.x, startPoint.y, x-startPoint.x, y - startPoint.y);topCtx.stroke();}//橡皮擦const drawEraser = (x,y)=>{//橡皮擦圆形半径const radius = lineWidth/2;botCtx.beginPath(); for(let i=0;i<radius*2;i++){//勾股定理高hlet h = Math.abs( radius - i); //i>radius h = i-radius; i<radius  h = radius - i//勾股定理llet l = Math.sqrt(radius*radius -h*h); //矩形高度let rectHeight = 1;//矩形宽度let rectWidth = 2*l;//矩形Xlet rectX = x-l;//矩形Ylet rectY = y-radius + i;botCtx.clearRect(rectX, rectY, rectWidth, rectHeight);}}//画透明度直线const drawLine = (x,y)=>{if(!isDown)return;//清空当前画布内容topCtx.clearRect(0,0,canvasWidth,canvasHeight);//必须每次都beginPath  不然会卡topCtx.beginPath();topCtx.moveTo(startPoint.x,startPoint.y);topCtx.lineTo(x,y);topCtx.stroke();}//画带透明度涂鸦const drawCurve = (x,y)=>{drawPoints.push({x,y});//清空当前画布内容topCtx.clearRect(0,0,canvasWidth,canvasHeight);//必须每次都beginPath  不然会卡topCtx.beginPath();topCtx.moveTo(drawPoints[0].x,drawPoints[0].y);for(let i=1;i<drawPoints.length;i++){topCtx.lineTo(drawPoints[i].x,drawPoints[i].y);}topCtx.stroke();}//切换操作const changeType = (type,that)=>{if(drawType == type) return;let tools = document.getElementsByClassName('img_tool');for(let i=0;i<tools.length;i++){let ele = tools[i];if(ele.classList.contains('img_tool_active'))ele.classList.remove('img_tool_active'); //ele.removeClassName('img_tool_active');}that.classList.add('img_tool_active');drawType = type;}//canvas添加鼠标事件topCan.addEventListener('mousedown',mousedown);topCan.addEventListener('mousemove',mousemove);topCan.addEventListener('mouseup',mouseup);//全局添加鼠标抬起事件document.addEventListener('mouseup',(e)=>{let x = (e||window.event).offsetX;let y = (e||window.event).offsetY;if(!isCanUp){if(drawType == 'line'){let clientX = topCan.getBoundingClientRect().x;let clientY = topCan.getBoundingClientRect().y;drawLine(x-clientX,y-clientY);}// topCan内容画到botCan上topToBot();}});//全局添加鼠标移动事件document.addEventListener('mousemove',(e)=>{if(isMove)return isMove = false;let x = (e||window.event).offsetX;let y = (e||window.event).offsetY;if(drawType == 'line'){let clientX = topCan.getBoundingClientRect().x;let clientY = topCan.getBoundingClientRect().y;drawLine(x-clientX,y-clientY);}});</script>
</body>
</html>