HTML5 Game - Springing to a moving target

Description

Springing to a moving target
Demo

<!doctype html>
<html>
  <head>
    <style>#canvas {background-color: grey;}</style>
  </head>/*  w  w  w .jav  a  2s  .c o  m*/
  <body>
    <canvas id="canvas" width="400" height="400"></canvas>
    <script>
      class Ball {  
constructor() {
     this.radius = 4;
       
     this.x = 0;  
     this.y = 0;  
     this.vx = 0;  
     this.vy = 0;  
     this.rotation = 0;  
     this.scaleX = 1;  
     this.scaleY = 1;  
     this.color = "#ff0000";
     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();  
     context.arc(0, 0, this.radius, 0, (Math.PI * 2), true);  
     context.closePath();  
  context.fill();  
  if (this.lineWidth > 0) {  
    context.stroke();  
  }  
  context.restore();  
}
getBounds() {  
  return {  
    x: this.x - this.radius,  
    y: this.y - this.radius,  
    width: this.radius * 2,  
    height: this.radius * 2  
  };  
}

}  function captureMouse(element) {
  let 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) {
    let 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 () {
      let canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          mouse = captureMouse(canvas),
          ball = new Ball(),
          spring = 0.03,
          friction = 0.95,
          vx = 0,
          vy = 0;

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

        let dx = mouse.x - ball.x,
            dy = mouse.y - ball.y,
            ax = dx * spring,
            ay = dy * spring;

        vx += ax;
        vy += ay;
        vx *= friction;
        vy *= friction;
        ball.x += vx;
        ball.y += vy;
        ball.draw(context);
      }());
    };
    </script>
  </body>
</html>
HTML5 Game - Springing to a moving target

Description

Demo

Related Topic
