canvas實現太陽、地球和月亮旋轉效果

admin發表於2017-02-22
Canvas
分享一段程式碼例項，它實現了地月系公轉效果。

程式碼例項如下:

[HTML] 純文字檢視 複製程式碼
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta name="author" content="http://www.softwhy.com/" />
<title>螞蟻部落</title>
</head>
<body>
<canvas id="myCanvas" width="800" height="550"></canvas>
<script type="text/javascript">
var sun = new Image();
var moon = new Image();
var earth = new Image();
function init(){
  sun.src = 'https://mdn.mozillademos.org/files/1456/Canvas_sun.png';
  moon.src = 'https://mdn.mozillademos.org/files/1443/Canvas_moon.png';
  earth.src = 'https://mdn.mozillademos.org/files/1429/Canvas_earth.png';
  window.requestAnimationFrame(draw);
}
 
function draw() {
  var ctx = document.getElementById('myCanvas').getContext('2d');
 
  ctx.globalCompositeOperation = 'destination-over';
  ctx.clearRect(0,0,300,300); // clear canvas
 
  ctx.fillStyle = 'rgba(0,0,0,0.4)';
  ctx.strokeStyle = 'rgba(0,153,255,0.4)';
  ctx.save();
  ctx.translate(150,150);
 
  // Earth
  var time = new Date();
  ctx.rotate( ((2*Math.PI)/60)*time.getSeconds() + ((2*Math.PI)/60000)*time.getMilliseconds() );
  ctx.translate(105,0);
  ctx.fillRect(0,-12,50,24); // Shadow
  ctx.drawImage(earth,-12,-12);
 
  // Moon
  ctx.save();
  ctx.rotate( ((2*Math.PI)/6)*time.getSeconds() + ((2*Math.PI)/6000)*time.getMilliseconds() );
  ctx.translate(0,28.5);
  ctx.drawImage(moon,-3.5,-3.5);
  ctx.restore();
 
  ctx.restore();
   
  ctx.beginPath();
  ctx.arc(150,150,105,0,Math.PI*2,false); // Earth orbit
  ctx.stroke();
  
  ctx.drawImage(sun,0,0,300,300);
 
  window.requestAnimationFrame(draw);
}
 
init();
</script>
</body>
</html>

圖片是引用的外網的，可能顯示會有所延遲。

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