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- <!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 ee=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；
以上就是本文的全部内容，希望对大家的学习有所帮助。
原文：http://www.cnblogs.com/jone-chen/p/5243439.html
