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Canvas - 如何通過(guò)設(shè)置其寬度和高度清除畫(huà)布

我們想知道如何通過(guò)設(shè)置其寬度和高度清除畫(huà)布。 





<!DOCTYPE html>

<html>
  <head>
    <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");
        
        context.fillStyle = "rgb(255, 0, 0)";
        
        context.fillRect(40, 40, 100, 100);
        
        context.beginPath();
        context.arc(230, 90, 50, 0, Math.PI*2, false);
        context.closePath();
        context.fill();
        
        //context.clearRect(230, 90, 50, 50);
        
        canvas.attr("width", canvas.width());
        canvas.attr("height", canvas.height());
        
        context.fillRect(40, 40, 100, 100);
      });
    </script>
  </head>
  
  <body>
    <canvas id="myCanvas" width="500" height="500">
      <!-- Insert fallback content here -->
    </canvas>
  </body>
</html>