title: Does Canvas redraw itself every time anything changes?
body: <p>I have done some research on how canvas works. It is supposed to be "immediate mode" means that it does not remember what its drawing looks like, only the bitmap remains everytime anything changes.</p>
  
  <p>This seems to suggest that canvas does not redraw itself on change.<br>
  However, when I tested canvas on iPad (basically I keep drawing parallel lines on the canvas), the frame rate degrades rapidly when there are more lines on the canvas. Lines are drawn more slowly and in a more jumpy way.</p>
  
  <p>Does this mean canvas actually have to draw the whole thing on change? Or there is other reason for this change in performance?</p>