HTML Canvas Animation Bouncing off boundary

Description

HTML Canvas Animation Bouncing off boundary

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<!DOCTYPE html>

<html>
  <head>
    <title>Making things move</title>
    <meta charset="utf-8">
    //from  w ww.ja  v a 2s . com
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
    
    <script type="text/javascript">
      $(document).ready(function() {  
        var canvas = $("#myCanvas");
        var context = canvas.get(0).getContext("2d");
        
        var canvasWidth = canvas.width();
        var canvasHeight = canvas.height();
        
        var playAnimation = true;
        
        var startButton = $("#startAnimation");
        var stopButton = $("#stopAnimation");
        
        startButton.hide();
        startButton.click(function() {
          $(this).hide();
          stopButton.show();
          
          playAnimation = true;
          animate();
        });
        
        stopButton.click(function() {
          $(this).hide();
          startButton.show();
          
          playAnimation = false;
        });
        
        // Class that defines new shapes to draw
        var Shape = function(x, y, width, height) {
          this.x = x;
          this.y = y;
          this.width = width;
          this.height = height;
          
          this.reverseX = true;
          this.reverseY = false;
        };
        
        // Array that holds all the shapes to draw
        var shapes = new Array();
        
        // Setting up some shapes
        for (var i = 0; i < 10; i++) {
          var x = Math.random()*250;
          var y = Math.random()*250;
          var width = height = Math.random()*30;
          shapes.push(new Shape(x, y, width, height));
        };
        
        // Animation loop that does all the fun stuff
        function animate() {
          // Clear
          context.clearRect(0, 0, canvasWidth, canvasHeight);
          
          // Loop through every object
          var shapesLength = shapes.length;
          for (var i = 0; i < shapesLength; i++) {
            var tmpShape = shapes[i];
            
            // Update
            // Check direction to move shape
            if (!tmpShape.reverseX) {
              tmpShape.x += 2;
            } else {
              tmpShape.x -= 2;
            };
            
            if (!tmpShape.reverseY) {
              tmpShape.y += 2;
            } else {
              tmpShape.y -= 2;
            };
            
            // Draw shape
            context.fillRect(tmpShape.x, tmpShape.y, tmpShape.width, tmpShape.height);
            
            // Check the boundaries
            if (tmpShape.x < 0) {
              tmpShape.reverseX = false;
            } else if (tmpShape.x + tmpShape.width > canvasWidth) {
              tmpShape.reverseX = true;
            };
            
            if (tmpShape.y < 0) {
              tmpShape.reverseY = false;
            } else if (tmpShape.y + tmpShape.height > canvasHeight) {
              tmpShape.reverseY = true;
            };

          };
          
          if (playAnimation) {
            // Run the animation loop again in 33 milliseconds
            setTimeout(animate, 33);
          };
        };
        
        // Start the animation loop
        animate();
      });
    </script>
  </head>
  
  <body>
    <canvas id="myCanvas" width="500" height="500">
      <!-- Insert fallback content here -->
    </canvas>
    <div>
      <button id="startAnimation">Start</button>
      <button id="stopAnimation">Stop</button>
    </div>
  </body>
</html>



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