动画原理——两点间的距离，点到鼠标的距离

书籍名称：HTML5-Animation-with-JavaScript

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

1.要求两点间的距离，只需要在直线上构建一个直角三角形，然后用勾股定理。如下图：

2.代码如下

10-distance.html

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Distance</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>
    <textarea id="log"></textarea>
    <aside>Refresh page for another calculation.</aside>
    
    <script src="../include/utils.js"></script>
    <script>
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          log = document.getElementById('log');

      //Create a black square, assign random position.
      var rect1 = {
        x: Math.random() * canvas.width,
        y: Math.random() * canvas.height
      };
      context.fillStyle = "#000000";
      context.fillRect(rect1.x - 2, rect1.y - 2, 4, 4);

      //Create a red square, assign random position.
      var rect2 = {
        x: Math.random() * canvas.width,
        y: Math.random() * canvas.height
      };
      context.fillStyle = "#ff0000";
      context.fillRect(rect2.x - 2, rect2.y - 2, 4, 4);

      //Calculate the distance between the two squares.
      var dx = rect1.x - rect2.x,
          dy = rect1.y - rect2.y,
          dist = Math.sqrt(dx * dx + dy * dy);
      
      //log output of distance value to screen
      log.value = "distance: " + dist;
    };
    </script>
  </body>
</html>

2.点到鼠标的距离，原理也是一样。

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Mouse Distance</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>
    <textarea id="log"></textarea>
    <aside>Move mouse on canvas element.</aside>
    
    <script src="../include/utils.js"></script>
    <script>
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          mouse = utils.captureMouse(canvas),
          log = document.getElementById('log'),
          rect = {x: canvas.width / 2, y: canvas.height / 2};
        
      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);
          
        var dx = rect.x - mouse.x,
            dy = rect.y - mouse.y,
            dist = Math.sqrt(dx * dx + dy * dy);
    
        //draw square
        context.fillStyle = "#000000";
        context.fillRect(rect.x - 2, rect.y - 2, 4, 4);
        //draw line
        context.beginPath();
        context.moveTo(rect.x, rect.y);
        context.lineTo(mouse.x, mouse.y);
        context.closePath();
        context.stroke();
    
        //log output of distance value to screen
        log.value = "distance: " + dist;
      }());
    };
    </script>
  </body>
</html>

posted on 2015-01-23 13:21 吹过的风阅读(225) 评论(0) 编辑收藏举报