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SubjectRe: [linux-fbdev] fbdev 2.4.0 cleanups
Russell King wrote:
> > Okay lets consider this. Now some video cards use different apertures for
> > their video memory. What I mean the framebuffer location is different for
> > 8 bit (it's little endian) and 16 bit (big endian). Consider this.
> > You start your X server in 8 bit mode. Now it will have write access to
> > /dev/fb. Now you start some app which opens /dev/fb in read only mode and
> > gets the current fix info. fix->smem_start will point to the little endian
> > aperture right. Now your X server has properly ALT whatever function keys
> > that do change the video mode. Since the X server has write access it can
> > change the modes. So now you switch to 16 bit color mode which means
> > fix->smem_start has changed to the big aperture. Your other app is still
> > writing to where the little endian aperture was which is the wrong place.
>
> Unless there has been a major change in X11, I don't think that's possible.
> I believe that the only thing that Alt +/- can do is change resolution, not
> colour depth.
>
> IIRC, colour depth requires a restart of the server and all applications.
>
> Please correct me if I'm wrong.

Well, with XFree86-4, the DGA extension as been updated to v2 from v1.1
and is said to allow depth change. But it's an XFree86 extension and is
not provided by other Xservers.
So you may change it while a program hold the whole screen, but not for
general use (ie changing depth a la windows, wm and other X apps won't
accept it nicely :-) )

--
www.linux-mandrake.com
somewhere between the playstation and the craystation
Thierry

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