title: Draw on a large canvas, scroll it, save it, reload it ... works, but only the viewport part is saved
body: <p>My program can draw 2D shapes on a canvas. The result can be scrolled. , When I save the result, then ONLY the image in the viewport is saved. </p>
  
  <p>I use a View and draw on it's canvas. </p>
  
  <p>Saving the drawing/updated result is: </p>
  
  <pre><code>setDrawingCacheEnabled(true);  
  buildDrawingCache();
  Bitmap bmp = Bitmap.createBitmap( this.getDrawingCache());   
  setDrawingCacheEnabled( false);    
  // the bitmap I can save into a file
  bm.compress( Bitmap.CompressFormat.PNG, 90, new FileOutputStream( new File( filepath)));
  </code></pre>
  
  <p>When I use a large view/canvas, then I get errors that my drawingCache is not big enough. When I use a regualar view/canvas size, then nearly all drawings outside the viewport are clipped. </p>
  
  <p>==> Can I draw on a bitmap and have that bitmap immediately drawn on the view's canvas? </p>
  
  <p>So, after some drawing, the initial bitmap is updated with the newly added drawing? </p>