title: How to make only particular area of canvas visible?
body: <p><strong>What I have :</strong></p>
  
  <p>Lets take a 500px wide canvas : </p>
  
  <pre><code>                     +---------+
   +-------------------------------------------------+
   |                   |         |                   |
   |    X      XXXX    | XXXXXX  |   X   X    XXXXX  |
   |  XXX     X   XX   |   XXXX  | XX    X    X      |
   |    X       XXXX   |  XXXX   | XX XXXXXX  XXXX   |
   |    X     XXX      |     XX  |       X       XXX |
   |  XXXX    XXXXXXX  | XXXXXX  |       X    X   XX |
   |                   |         |            XXXXX  |
   +-------------------------------------------------+
  x=0                  +---------+                   x=500
                       x=200     x=300
  </code></pre>
  
  <p>Different drawing are there in different part of canvas. </p>
  
  <p><strong>What I want :</strong></p>
  
  <p>I want to make visible only 1/5 of canvas. Suppose in above diagram x=200 to 300 should be visible. </p>
  
  <p>Ultimately I want to change visible area and produce a slide left or right effect in canvas.</p>
  
  <p>Any Help and lead is appreciated :)</p>