HTML Canvas Remove object from canvas

Description

HTML Canvas Remove object from canvas

View in separate window 

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Removal</title>
  </head>/*from ww w . j  a  v a2 s  .c o m*/
  <body>
    <canvas id="canvas" width="400" height="400"></canvas>
    <textarea id="log"></textarea>
    <script>
class Ball {
  constructor() {
    this.x = 0;
    this.y = 0;
    this.radius = 30;
    this.vx = 0;
    this.vy = 0;
    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'),
          log = document.getElementById('log'),
          balls = [],
          numBalls = 10;

      for (var ball, i = 0; i < numBalls; i++) {
        ball = new Ball(20);
        ball.id = "ball" + i;
        ball.x  = Math.random() * canvas.width;
        ball.y  = Math.random() * canvas.height;
        ball.vx = Math.random() * 2 - 1;
        ball.vy = Math.random() * 2 - 1;
        balls.push(ball);
      }

      function draw (ball, pos) {
        ball.x += ball.vx;
        ball.y += ball.vy;
        if (ball.x - ball.radius > canvas.width ||
            ball.x + ball.radius < 0 ||
            ball.y - ball.radius > canvas.height ||
            ball.y + ball.radius < 0) {
          balls.splice(pos, 1); //remove ball from array
          if (balls.length > 0) {
            log.value = "Removed " + ball.id;
          } else {
            log.value = "All gone!";
          }
        }
        ball.draw(context);
      }

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

        var i = balls.length;
        while (i--) {
          draw(balls[i], i);
        }
      }());
    };
    </script>
  </body>
</html>



PreviousNext

Related