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  1. #1
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    Redraw stores and treatment of bitmaps

    I am trying to grasp the concept of redraw stores in Symbian^3 (http://library.developer.nokia.com/i...7BB5FC0AC.html) and I have a question about treatment of bitmaps.

    My understanding is that redraw stores store the sequences of drawing commands so that the window server can replay them when needed.
    My deduction is that this means that the commands may be played in a different thread than the application thread.
    My question is: what if the command is a bitmap BitBlt command? Does it mean that the app should not update the bitmap because the window server may replay the BitBlt command in a different thread while the app is not yet done updating the bitmap (i.e. flicker)?

    If that is the case, I am surprised this is not more widely discussed/documented and why this is not included in the differences between S60 5th and Symbian^3 (http://library.developer.nokia.com/i...7BB5FC0AC.html).
    So I am thinking I am getting it wrong about redraw stores...

    Thanks in advance for any comment or suggestion appreciated!
    sergiogiogio
    Last edited by sergiogiogio; 2012-06-14 at 07:18. Reason: title typo

  2. #2
    Nokia Developer Moderator
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    Re: Redraw stores and tratment of bitmaps

    in essence that method has been always used in Symbian. Basically stuff written in Draw, is not executed strait away, but commands are "stored" and then executed in batches. i.e. it does actually lessen the risk of flickering.

  3. #3
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    Re: Redraw stores and tratment of bitmaps

    Thanks a lot for your quick answer, I did not realize that it had always been the case.
    But then this means that the double buffering technique presented in the wiki (http://www.developer.nokia.com/Commu...uble_buffering) does actually *not* guarantee flicker free animation.
    So ... to guarantee flicker free animation we should write the scene directly to the RWindow graphic context (in Draw) and ensure that the redraw batch does not exceed the size of the window server input queue? Is that correct?

  4. #4
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    Re: Redraw stores and tratment of bitmaps

    Quote Originally Posted by sergiogiogio View Post
    Thanks a lot for your quick answer, I did not realize that it had always been the case.
    But then this means that the double buffering technique presented in the wiki (http://www.developer.nokia.com/Commu...uble_buffering) does actually *not* guarantee flicker free animation.
    So ... to guarantee flicker free animation we should write the scene directly to the RWindow graphic context (in Draw) and ensure that the redraw batch does not exceed the size of the window server input queue? Is that correct?
    I have no clue on how you get that idea from there.. Anyway, if you use double buffering, then in essense your draw function will only draw each pixel once, thus it prevents the flickering as much as is possible.

  5. #5
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    Re: Redraw stores and tratment of bitmaps

    The double buffering technique basically says:
    1- draw the scene to an offscreen bitmap when needed
    2- Bitblt the offscreen bitmap to the screen in Draw()

    My point is that since the Bitblt command in Draw() is executed in a different thread, it may be executed while the application thread is doing the first operation (draw the scene to the offscreen bitmap). If that is the case, flicker will occur because the scene is partially drawn in the offscreen bitmap at this point.

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