动画原理——旋转

书籍名称：HTML5-Animation-with-JavaScript

书籍源码：https://github.com/lamberta/html5-animation1

1.简单旋转

利用三角函数进行旋转

01-rotate-1.html

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Rotate 1</title>
    <link rel="stylesheet" href="../include/style.css">
  </head>
  <body>
    <header>
      Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a>
    </header>
    <canvas id="canvas" width="400" height="400"></canvas>

    <script src="../include/utils.js"></script>
    <script src="./classes/ball.js"></script>
    <script>
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          ball = new Ball(),
          vr = 0.05,
          angle = 0,
          radius = 150,
          centerX = canvas.width / 2,
          centerY = canvas.height / 2;
      
      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);
        
        ball.x = centerX + Math.cos(angle) * radius;
        ball.y = centerY + Math.sin(angle) * radius;
        angle += vr;
        
        ball.draw(context);
      }());
    };
    </script>
  </body>
</html>

View Code

2.高级旋转

这种方法是根据当前的角度和坐标，计算下一帧的角度和坐标
02-rotate-2.html

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Rotate 2</title>
    <link rel="stylesheet" href="../include/style.css">
  </head>
  <body>
    <header>
      Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a>
    </header>
    <canvas id="canvas" width="400" height="400"></canvas>

    <script src="../include/utils.js"></script>
    <script src="./classes/ball.js"></script>
    <script>
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          ball = new Ball(),
          vr = 0.05,
          cos = Math.cos(vr),
          sin = Math.sin(vr),
          centerX = canvas.width / 2,
          centerY = canvas.height / 2;
      
      ball.x = Math.random() * canvas.width;
      ball.y = Math.random() * canvas.height;

      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);
        
        var x1 = ball.x - centerX,
            y1 = ball.y - centerY,
            x2 = cos * x1 - sin * y1,
            y2 = cos * y1 + sin * x1;
        
        ball.x = centerX + x2;
        ball.y = centerY + y2;
        
        ball.draw(context);
      }());
    };
    </script>
  </body>
</html>

View Code

多个物体

03-rotate-3.html

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Rotate 3</title>
    <link rel="stylesheet" href="../include/style.css">
  </head>
  <body>
    <header>
      Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a>
    </header>
    <canvas id="canvas" width="400" height="400"></canvas>
    <aside>Move mouse left or right on canvas element.</aside>

    <script src="../include/utils.js"></script>
    <script src="./classes/ball.js"></script>
    <script>
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          mouse = utils.captureMouse(canvas),
          balls = [],
          numBalls = 10,
          vr = 0.05,
          centerX = canvas.width / 2,
          centerY = canvas.height / 2,
          cos, sin; //accessible by move and drawFrame

      for (var ball, i = 0; i < numBalls; i++) {
        ball = new Ball();
        ball.x = Math.random() * canvas.width;
        ball.y = Math.random() * canvas.height;
        balls.push(ball);
      }

      function move (ball) {
        var x1 = ball.x - centerX,
            y1 = ball.y - centerY,
            x2 = cos * x1 - sin * y1,
            y2 = cos * y1 + sin * x1;
        ball.x = centerX + x2;
        ball.y = centerY + y2;
      }
      
      function draw (ball) {
        ball.draw(context);
      }

      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);
        
        var angle = (mouse.x - centerX) * 0.0005;
        cos = Math.cos(angle);
        sin = Math.sin(angle);
        balls.forEach(move);
        balls.forEach(draw);
      }());
    };
    </script>
  </body>
</html>

View Code

3.在有角度的情况下反弹

posted on 2015-01-31 11:46 吹过的风阅读(293) 评论(0) 收藏举报