<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <title>canvas实现跟随鼠标旋转的箭头</title> <style> *{padding: 0;margin: 0} </style> </head> <body> <canvas width="500" height="500" style="border: 1px solid #555; display: block;margin: 0 auto;"></canvas> <script> var arrow=function () { this.x=0; this.y=0; this.color="#f90" this.rolation=0; } var canvas=document.querySelector('canvas') var ctx=canvas.getContext('2d'); arrow.prototype.draw=function (ctx) { ctx.save(); ctx.translate(this.x,this.y); ctx.rotate(this.rolation) ctx.fillStyle=this.color; ctx.beginPath(); ctx.moveTo(0, 15); ctx.lineTo(-50, 15); ctx.lineTo(-50, -15); ctx.lineTo(0,-15); ctx.lineTo(0,-35); ctx.lineTo(50,0); ctx.lineTo(0,35); ctx.closePath() ctx.fill(); ctx.restore(); } var Arrow=new arrow(); Arrow.x=canvas.width/2; Arrow.y=canvas.height/2; var c_x,c_y; //相对于canvas坐标的位置； var isMouseDown=false; Arrow.draw(ctx) canvas.addEventListener('mousedown',function(e) { isMouseDown=true; },false) canvas.addEventListener('mousemove',function(e) { if(isMouseDown==true){ c_x=getPos(e).x-canvas.offsetLeft; c_y=getPos(e).y-canvas.offsetTop; //setInterval(drawFram,1000/60) requestAnimationFrame(drawFram) } },false) canvas.addEventListener('mouseup',function(e) { isMouseDown=false; },false) function drawFram(){ var dx=c_x-Arrow.x; var dy=c_y-Arrow.y; Arrow.rolation=Math.atan2(dy,dx); ctx.clearRect(0,0,canvas.width,canvas.height); Arrow.draw(ctx) } function getPos(e) { var mouse={x:0,y:0} var e=e||event; if(e.pageX||e.pageY){ mouse.x=e.pageX; mouse.y=e.pageY; }else{ mouse.x=e.pageX+document.body.scrollLeft+document.document.documentElement.scrollLeft; mouse.y=e.pageY+document.body.scrollTop+document.document.documentElement.scrollTop; } return mouse; } </script> </body> </html>
DEMO地址：http://codepen.io/jonechen/pen/eZpgWd
不废话，直接上DEMO了，这个效果实现起来并不复杂，但是麻雀随小，五脏俱全，主要涉及到的知识点有：
1、canvas的基本绘图；
2、js各个事件的监听；
3、js动画；
4、三角函数结合js在canvas中的基本应用；