HTML Canvas Math Mouse Distance

Description

HTML Canvas Math Mouse Distance

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<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Mouse Distance</title>
  </head>//from ww w .j a  va2 s. c  om
  <body>
    <canvas id="canvas" width="400" height="400"></canvas>
    <textarea id="log"></textarea>
    <aside>Move mouse on canvas element.</aside>
    <script>
captureMouse = function (element) {
  var mouse = {x: 0, y: 0, event: null},
      body_scrollLeft = document.body.scrollLeft,
      element_scrollLeft = document.documentElement.scrollLeft,
      body_scrollTop = document.body.scrollTop,
      element_scrollTop = document.documentElement.scrollTop,
      offsetLeft = element.offsetLeft,
      offsetTop = element.offsetTop;
  
  element.addEventListener('mousemove', function (event) {
    var x, y;
    
    if (event.pageX || event.pageY) {
      x = event.pageX;
      y = event.pageY;
    } else {
      x = event.clientX + body_scrollLeft + element_scrollLeft;
      y = event.clientY + body_scrollTop + element_scrollTop;
    }
    x -= offsetLeft;
    y -= offsetTop;
    
    mouse.x = x;
    mouse.y = y;
    mouse.event = event;
  }, false);
  
  return mouse;
}; 
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          mouse = 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>



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