HTML Canvas Animation Flow Mouse Move for Arrow Shape

Description

HTML Canvas Animation Flow Mouse Move for Arrow Shape

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<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Rotate to Mouse</title>
  </head>//  w w w  .jav  a  2 s  .com
  <body>
    <canvas id="canvas" width="400" height="400"></canvas>
    <aside>Move mouse on canvas element.</aside>
    <script>
class Arrow {
  constructor() {
    this.x = 0;
    this.y = 0;
    this.color = "#ffff00";
    this.rotation = 0;
  }

  draw(context) {
    context.save();
    context.translate(this.x, this.y);
    context.rotate(this.rotation);
    
    context.lineWidth = 2;
    context.fillStyle = this.color;
    context.beginPath();
    context.moveTo(-50, -25);
    context.lineTo(0, -25);
    context.lineTo(0, -50);
    context.lineTo(50, 0);
    context.lineTo(0, 50);
    context.lineTo(0, 25);
    context.lineTo(-50, 25);
    context.lineTo(-50, -25);
    context.closePath();
    context.fill();
    context.stroke();
    
    context.restore();
  }
}
    
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),
          arrow = new Arrow();
        
      arrow.x = canvas.width / 2;
      arrow.y = canvas.height / 2;
        
      (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;
          
        arrow.rotation = Math.atan2(dy, dx); //radians
        arrow.draw(context);
      }());
    };
    </script>
  </body>
</html>



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