html5 canvas implements arrows that follow the mouse rotation_html5 tutorial skills-H5 Tutorial-php.cn

html5 canvas implements arrows that follow the mouse rotation_html5 tutorial skills

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Release： 2016-05-16 15:51:42

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>
<html>
<head>
<meta charset="utf- 8" />
Content = " ie = edge " /// > <title>canvas implements arrows that follow the mouse rotation < /
> <style>
style>
head>
<body>
<canvas width=
height="500" style="border: 1px solid #555; display: block;margin: 0 auto;">canvas > <script>
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;

script

> body> html> DEMO address:

http://codepen.io/jonechen/pen/eZpgWd

No nonsense, let’s go straight to the DEMO. This effect is not complicated to achieve, but it is as small as a sparrow and has all the internal organs. The main knowledge points involved are: 1. Basic drawing of canvas;

2. Monitoring of various js events;

3. js animation;

4. Basic application of trigonometric functions combined with js in canvas;

The above is the entire content of this article, I hope it will be helpful to everyone’s study.

Original text:

http://www.cnblogs.com/jone-chen/p/5243439.html