HTML Canvas Touch Event 2

Description

HTML Canvas Touch Event 2

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<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Touch Events</title>
    <meta name="viewport" content="width=device-width,initial-scale=1.0,user-scalable=no">
  </head>//  ww  w . j  a v  a 2  s.  c o m
  <body>
    <canvas id="canvas" width="400" height="400"></canvas>
    <textarea id="log"></textarea>
    <aside>Press and move touch inside and outside of circle (touch-capable device required).</aside>
    <script>
class Ball {
  constructor(radius, color) {
    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();
  }

  getBounds() {
    return {
      x: this.x - this.radius,
      y: this.y - this.radius,
      width: this.radius * 2,
      height: this.radius * 2
    };
  }
}
containsPoint = function (rect, x, y) {
  return !(x < rect.x ||
           x > rect.x + rect.width ||
           y < rect.y ||
           y > rect.y + rect.height);
};
captureTouch = function (element) {
  var touch = {x: null, y: null, isPressed: false, 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('touchstart', function (event) {
    touch.isPressed = true;
    touch.event = event;
  }, false);

  element.addEventListener('touchend', function (event) {
    touch.isPressed = false;
    touch.x = null;
    touch.y = null;
    touch.event = event;
  }, false);
  
  element.addEventListener('touchmove', function (event) {
    var x, y,
        touch_event = event.touches[0]; //first touch
    
    if (touch_event.pageX || touch_event.pageY) {
      x = touch_event.pageX;
      y = touch_event.pageY;
    } else {
      x = touch_event.clientX + body_scrollLeft + element_scrollLeft;
      y = touch_event.clientY + body_scrollTop + element_scrollTop;
    }
    x -= offsetLeft;
    y -= offsetTop;
    
    touch.x = x;
    touch.y = y;
    touch.event = event;
  }, false);
  
  return touch;
};
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          touch = captureTouch(canvas),
          log = document.getElementById('log'),
          ball = new Ball();

      ball.x = canvas.width / 2;
      ball.y = canvas.height / 2;
      ball.draw(context);
      
      canvas.addEventListener('touchstart', function (event) {
        event.preventDefault();
        if (containsPoint(ball.getBounds(), touch.x, touch.y)) {
          log.value = "in ball: touchstart";
        } else {
          log.value = "canvas: touchstart";
        }
      }, false);

      canvas.addEventListener('touchend', function (event) {
        event.preventDefault();
        log.value = "canvas: touchend";
      }, false);

      canvas.addEventListener('touchmove', function (event) {
        event.preventDefault();
        if (containsPoint(ball.getBounds(), touch.x, touch.y)) {
          log.value = "in ball: touchmove";
        } else {
          log.value = "canvas: touchmove";
        }
      }, false);
    };
    </script>
  </body>
</html>



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