[SDL] Re: why the sdl window is always top most in windows?

stand_fucai at hotmail.com stand_fucai at hotmail.com
Wed Jul 31 21:10:01 PDT 2002

thanks for your answers!

How can I complete the overlay implementation ? Where I can find the reference?

----- Original Message ----- 
From: "Gabriele Greco" <gabrielegreco at tin.it>
Newsgroups: loki.open-source.sdl
To: <sdl at libsdl.org>
Sent: Tuesday, July 23, 2002 11:57 PM
Subject: Re: [SDL] Re: why the sdl window is always top most in windows?

> On Tue, 2002-07-23 at 17:27, Pete Shinners wrote:
> > SDL is using your video card's "video overlay" planes. this is a special 
> > part of video card memory that lives in a different colorspace than the 
> > normal rgb desktop. this video overlay is always on top of anything else on 
> > the screen (sort of like how video cards usually draw the mouse in a 
> > separate overlay, so nothing can cover it)
> This is not necessary true.
> DirectX supports colorkeying overlay with most cards (at least NVIDIA
> and Matrox ones), this method is used also by XVideo extension as
> default.
> So SDL hw overlays DON'T stay on top of every window in the X enviroment
> (with Xvideo extension) but they does in win32 enviroment since the SDL
> overlay support use the "simple" overlay method and not the colorkey
> one. 
> I suppose they use the simple one since directx colorkeying has a lot of
> problems with 16bit depth desktops where you risk to get you colorkey
> color dithered by windows. Anyway these problems can be avoided, I hope
> to see a more complete win32 overlay implementation in the next versions
> of SDL (I don't dare to do it myself since I hate directx programming,
> never seen a wrost API, expecially for 2d and sound stuff, also C=64
> GEOS was more friendly... )
> Bye,
>  Gabry

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