动画原理——速率

最新推荐文章于 2021-11-10 11:11:26 发布

转载最新推荐文章于 2021-11-10 11:11:26 发布 · 254 阅读

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CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/winderby/p/4253121.html

书籍名称：HTML5-Animation-with-JavaScript

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

1.在某一方向的方向的速率

本例掩饰水平的vx

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Velocity 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(),
          vx = 1;

      ball.x = 50;
      ball.y = 100;

      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);
          
        ball.x += vx;
        ball.draw(context);
      }());
    };
    </script>
  </body>
</html>

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2.在两个方向的速率

和第一个差不多，但有两个速率.

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Velocity 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(),
          vx = 1,
          vy = 1;

      ball.x = 50;
      ball.y = 100;
        
      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);

        ball.x += vx;
        ball.y += vy;
        ball.draw(context);
      }());
    };
    </script>
  </body>
</html>

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3.用三角函数生成的各个方向的速率

根据向量加法，和三角函数可以将某个方向的速率分解成两个方向。

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Velocity Angle</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(),
          angle = 45,
          speed = 1;

      ball.x = 50;
      ball.y = 100;

      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);

        var radians = angle * Math.PI / 180,
            vx = Math.cos(radians) * speed,
            vy = Math.sin(radians) * speed;

        ball.x += vx;
        ball.y += vy;
        ball.draw(context);
      }());
    };
    </script>
  </body>
</html>

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4.箭头跟随程序

关键点：1.根据箭头的位置和鼠标的位置判断箭头倾斜的角度。

2.根据角度将速率分解X,Y方向的速率。

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Follow Mouse 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>
    <aside>Move mouse on canvas element.</aside>

    <script src="../include/utils.js"></script>
    <script src="./classes/arrow.js"></script>
    <script>
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          mouse = utils.captureMouse(canvas),
          arrow = new Arrow(),
          speed = 3;
        
      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);

        var dx = mouse.x - arrow.x,
            dy = mouse.y - arrow.y,
            angle = Math.atan2(dy, dx),
            vx = Math.cos(angle) * speed,
            vy = Math.sin(angle) * speed;

        arrow.rotation = angle; //radians
        arrow.x += vx;
        arrow.y += vy;
        arrow.draw(context);
      }());
    };
    </script>
  </body>
</html>

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5.旋转

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Rotational Velocity</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/arrow.js"></script>
    <script>
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          mouse = utils.captureMouse(canvas),
          arrow = new Arrow(),
          vr = 2; //degrees

      arrow.x = canvas.width / 2;
      arrow.y = canvas.height / 2;

      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);

        arrow.rotation += vr  * Math.PI / 180; //to radians
        arrow.draw(context);
      }());
    };
    </script>
  </body>
</html>

View Code

转载于:https://www.cnblogs.com/winderby/p/4253121.html