使用Canvas怎么绘制一个波浪花环？针对这个问题，这篇文章详细介绍了相对应的分析和解答，希望可以帮助更多想解决这个问题的小伙伴找到更简单易行的方法。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
body {
background: #111;
padding:0;
margin:0;
overflow:hidden;
}
</style>
</head>
<body>
<div id="wrapper"></div>
</body>
<script>
(function(){
'use strict';
let wrapper, canvas, ctx, width, height,
Tau=Math.PI*2, PI180=Math.PI/180,
systems=[];
/* PlanetarySystem */
let PlanetarySystem = function(id='pSys'){
Object.defineProperty(this, 'id', { value:id, writable:true} );
Object.defineProperty(this, 'x', { value:0, writable:true });
Object.defineProperty(this, 'y', { value:0, writable:true });
Object.defineProperty(this, 'allBodies', { value:[], writable:true });
Object.defineProperty(this, 'allBodiesLookup', { value:{}, writable:true }); // fast id lookup for children
Object.defineProperty(this, 'numBodies', { value:0, writable:true });
}
PlanetarySystem.prototype.addBody = function(vo) {
vo.parentSystem = this;
vo.parentBody = vo.parentBody === null ? this : this.allBodiesLookup[vo.parentBody];
let body = new PlanetaryBody(vo);
body.update();
this.allBodies.push(body);
this.allBodiesLookup[vo.id] = body;
this.numBodies += 1;
}
PlanetarySystem.prototype.setSpeedFactor = function(value){
let body;
for(let i=0; i<this.numBodies; i++){
body = this.allBodies[i];
body.setSpeedFactor(value);
}
}
PlanetarySystem.prototype.update = function(){
let body;
for(let i=0; i<this.numBodies; i++){
body = this.allBodies[i];
body.update();
}
}
/* PlanetaryBody */
let PlanetaryBody = function(vo){
Object.defineProperty(this, 'id', { value:vo.id, writable:true} );
Object.defineProperty(this, 'diameter', { value:vo.diameter, writable:true });
Object.defineProperty(this, 'colour', { value:vo.colour, writable:true });
Object.defineProperty(this, 'x', { value:0, writable:true });
Object.defineProperty(this, 'y', { value:0, writable:true });
Object.defineProperty(this, 'vx', { value:0, writable:true });
Object.defineProperty(this, 'vy', { value:0, writable:true });
Object.defineProperty(this, 'degrees', { value:vo.degrees, writable:true });
Object.defineProperty(this, 'speedBase', { value:vo.speed, writable:true });
Object.defineProperty(this, 'speed', { value:vo.speed , writable:true });
Object.defineProperty(this, 'orbitalRadius', { value:vo.orbitalRadius, writable:true });
Object.defineProperty(this, 'parentSystem', { value:vo.parentSystem, writable:true });
Object.defineProperty(this, 'parentBody', { value:vo.parentBody, writable:true });
return this;
}
PlanetaryBody.prototype.update = function(){
let angle = this.degrees * PI180;
this.degrees += this.speed;
this.vx = this.orbitalRadius * Math.cos(angle);
this.vy = this.orbitalRadius * Math.sin(angle);
// update position
if(this.parentBody != null){
this.x = this.vx + this.parentBody.x;
this.y = this.vy + this.parentBody.y;
}
}
/* init() */
function init(){
wrapper = document.querySelector('#wrapper');
canvas = createCanvas('canvas', width, height);
wrapper.appendChild(canvas);
ctx = canvas.getContext('2d');
setupEvents();
resizeCanvas();
/* Define new PlanetarySystem and set values */
let system1 = new PlanetarySystem('pSys1');
systems.push(system1);
system1.x = width * .5;
system1.y = height * .5;
system1.addBody({id:'sun', diameter:5, degrees:0, speed:0, colour:'#FDFE1D', orbitalRadius:0, parentBody:null});
for(let loop=30, i=0; i<loop; i+=1){
system1.addBody({ id: 'ball'+i,
diameter: 5,
degrees: 0,
speed: 2 + (loop * 0.15) - (i* 0.2),
colour: '#FDFE1D',
orbitalRadius: 7*(i+1),
parentBody: 'sun'});
}
}
/* Methods */
function createCanvas(id, w, h){
let tCanvas = document.createElement('canvas');
tCanvas.width = w;
tCanvas.height = h;
tCanvas.id = id;
return tCanvas;
}
function setupEvents(){
window.onresize = resizeCanvas;
}
function resizeCanvas(){
let rect = wrapper.getBoundingClientRect();
width = window.innerWidth;
height = window.innerHeight - rect.top -2;
canvas.width = width;
canvas.height = height;
for(let i=0; i<systems.length; i++){
systems[i].x = width * .5;
systems[i].y = height * .5;
}
}
function update(){
for(let loop=systems.length, i=0; i<loop; i++){
systems[i].update();
}
}
function draw(){
let system;
let prev = null;
for(let i=0; i<systems.length; i++){
system = systems[i];
let planetaryBody;
for(let loop=system.numBodies, j=1; j<loop; j+=1) {
planetaryBody = system.allBodies[j];
ctx.beginPath();
ctx.arc(planetaryBody.x, planetaryBody.y, planetaryBody.diameter, 0, Tau, false);
ctx.fillStyle = planetaryBody.colour;
ctx.fill();
if(j>1){
ctx.strokeStyle = planetaryBody.colour;
ctx.lineWidth = 2;
ctx.beginPath();
ctx.moveTo(planetaryBody.x, planetaryBody.y);
ctx.lineTo(prev.x, prev.y);
ctx.stroke();
}
prev = {x:planetaryBody.x, y:planetaryBody.y};
}
}
}
function animate(){
ctx.fillStyle = 'rgba(0,0,0, .05)';
ctx.fillRect(0, 0, width, height);
update();
draw();
requestAnimationFrame(animate);
}
init();
animate();
}());
</script>
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