display modes

Lionel Ulmer lionel.ulmer at free.fr
Mon Sep 29 02:38:01 CDT 2003

On Sun, Sep 28, 2003 at 06:51:24PM -0500, Alex Pasadyn wrote:
> The 24-bit X server depth corresponds to the 32-bit Windows depth.  I 
> never fully understood that.

That's not entirely true... There is not really the notion of 'bits per
pixel' in X. You only have depth (being the number of significant bits per
pixel). So a card with depth 24 can either be in a 24/24 mode (ie one pixel
being 3 bytes - being the 'depth 24' of Windows) or a 24/32 mode (one pixel
== 4 bytes - being the 'depth 32' of Windows).

Note that the 24/24 mode is pretty deprecated now (I think my NVIDIA driver
does not even support it at all) and this is why we mostly only report 8 /
16 / 32.

> My original patch returned a "bad mode" error if you tried to change the 
> depth, but it seems some applications just assume they can always change 
> the depth to whatever they want. 

Well, AFAIK, all Windows drivers enable to change the depth on the fly
without reboot.

> I was always concerned about faking it like that, but most apps 
> seem to be okay.  If they query the settings back they will see the 
> "real" depth and that their change to it had no effect.

Anyway, this is OK for DirectX .. as it has its own integrated depth
conversion routines (which I introduced for the aforementionned Jedi Knight
which used 8 bpp for the menu and 16 bpp for the game).


		 Lionel Ulmer - http://www.bbrox.org/

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