HTML Canvas Mouse Press, drag, and throw circle

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HTML Canvas Mouse Press, drag, and throw circle

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<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Throwing</title>
  </head>/*from   www  .j a va2 s .co  m*/
  <body>
    <canvas id="canvas" width="400" height="400"></canvas>
    <aside>Press, drag, and throw circle with mouse.</aside>
    <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();
  }

  getBounds() {
    return {
      x: this.x - this.radius,
      y: this.y - this.radius,
      width: this.radius * 2,
      height: this.radius * 2
    };
  }
}
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;
};  
containsPoint = function (rect, x, y) {
  return !(x < rect.x ||
           x > rect.x + rect.width ||
           y < rect.y ||
           y > rect.y + rect.height);
};
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          mouse = captureMouse(canvas),
          ball = new Ball(),
          vx = Math.random() * 10 - 5,
          vy = -10,
          bounce = -0.7,
          gravity = 0.2,
          isMouseDown = false,
          oldX, oldY;

      ball.x = canvas.width / 2;
      ball.y = canvas.height / 2;
      
      canvas.addEventListener('mousedown', function () {
        if (containsPoint(ball.getBounds(), mouse.x, mouse.y)) {
          isMouseDown = true;
          oldX = ball.x;
          oldY = ball.y;
          canvas.addEventListener('mouseup', onMouseUp, false);
          canvas.addEventListener('mousemove', onMouseMove, false);
        }
      }, false);
      
      function onMouseUp () {
        isMouseDown = false;
        canvas.removeEventListener('mouseup', onMouseUp, false);
        canvas.removeEventListener('mousemove', onMouseMove, false);
      }
      
      function onMouseMove (event) {
        ball.x = mouse.x;
        ball.y = mouse.y;
      }

      function trackVelocity () {
        vx = ball.x - oldX;
        vy = ball.y - oldY;
        oldX = ball.x;
        oldY = ball.y;
      }

      function checkBoundaries () {
        var left = 0,
            right = canvas.width,
            top = 0,
            bottom = canvas.height;
        
        vy += gravity;
        ball.x += vx;
        ball.y += vy;
        //boundary detect and bounce
        if (ball.x + ball.radius > right) {
          ball.x = right - ball.radius;
          vx *= bounce;
        } else if (ball.x - ball.radius < left) {
          ball.x = left + ball.radius;
          vx *= bounce;
        }
        if (ball.y + ball.radius > bottom) {
          ball.y = bottom - ball.radius;
          vy *= bounce;
        } else if (ball.y - ball.radius < top) {
          ball.y = top + ball.radius;
          vy *= bounce;
        }
      }

      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);
        
        if (isMouseDown) {
          trackVelocity();
        } else {
          checkBoundaries();
        }
        ball.draw(context);
      }());
    };
    </script>
  </body>
</html>



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