HTML Canvas Move shape with Acceleration via key board

Description

HTML Canvas Move shape with Acceleration via key board

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<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Acceleration 2</title>
  </head>//w ww .j av a  2s  . c o  m
  <body>
    <canvas id="canvas" width="400" height="400"></canvas>
    <aside>Press left and right arrow keys.</aside>
    <script>
class Ball {
  constructor() {
    this.x = 0;
    this.y = 0;
    this.radius = 40;
    this.rotation = 0;
    this.scaleX = 1;
    this.scaleY = 1;
    this.color = "blue";
    this.lineWidth = 1;
  }

  draw(context) {
    context.save();
    context.translate(this.x, this.y);
    context.rotate(this.rotation);
    context.scale(this.scaleX, this.scaleY);
    
    context.lineWidth = this.lineWidth;
    context.fillStyle = this.color;
    context.beginPath();
    //x, y, radius, start_angle, end_angle, anti-clockwise
    context.arc(0, 0, this.radius, 0, Math.PI * 2, true);
    context.closePath();
    context.fill();
    if (this.lineWidth > 0) {
      context.stroke();
    }
    context.restore();
  }
}
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          ball = new Ball(),
          vx = 0,
          ax = 0;

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

      window.addEventListener('keydown', function (event) {
        if (event.keyCode === 37) {         //left
          ax = -0.1;
        } else if (event.keyCode === 39) {  //right
          ax = 0.1;
        }
      }, false);

      window.addEventListener('keyup', function () {
        ax = 0;
      }, false);
        
      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);

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



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