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Thread: Drawing on a transparent window

  1. #1
    Junior Member Newbie
    Join Date
    Aug 2009

    Drawing on a transparent window

    Hello all,

    My goal is to draw an OpenGL object without drawing the background so that it looks as if the object is floating directly over the desktop. What would be the best way to accomplish this?

    As of right now I am drawing to a pixel buffer and have achieved a transparent background, but I do not know how to get that onto the screen. I heard there was a way to use GDI to draw it to the screen using BitBlt(), but I have no idea how to do that. If you could provide code samples, that would be the best, but any help is appreciated.

    BTW: I am using developing my app using Qt 4.5 on Windows XP.

    This is basically what I want to accomplish:

  2. #2
    Senior Member Regular Contributor LangFox's Avatar
    Join Date
    Oct 2001
    Shen Zhen, Guangdong, China

    Re: Drawing on a transparent window

    1, Set up the pfd with alpha bits.
    2, Render scene and get pixels.
    3, Create a layered window, bitblt pixels to it.
    Best Regards,

  3. #3
    Senior Member Frequent Contributor
    Join Date
    Dec 2007

    Re: Drawing on a transparent window

    There isn't a faster way to do that?
    This method involves GPU data to be transferred to client memory and then output it.
    If somebody would like to do something like this under Windows and wants good performance then one has to stick to DX?
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