[Novalug] Fedora 12 video question

greg pryzby greg@pryzby.org
Wed Oct 21 22:55:56 EDT 2009


On 10/21/2009 02:57 PM, Bryan J. Smith wrote:
> Your first comment didn't answer my question.
>
> If it's X itself, then it's typically not the X driver, but Xinerama.
> It is defining two displays, and then uses Xinerama to make them one.
> That doesn't support overlays, at least on both displays.

I didn't answer because I don't have access right now to the laptop. I 
explained how I got to the menu (or thought I did)
    System -> Preferences -> display
when I have the laptop I will run it the command, see what is running 
before and after to try and figure out if it is Xinerama or not.

One of the downsides of 'this modern linux' is being removed from that 
is doing the work.... I am clicking and not setting up via config files 
or from the command line any more :(

> The other approach is where the X driver "fools" the X system into
> thinking you have a "double-wide" monitor, with an unified framebuffer.
> Never seen i810 do that myself, only nVidia and ATI closed source.
>
> ________________________________
> From: greg pryzby<greg@pryzby.org>
>
> On Wed, Oct 21, 2009 at 11:56 AM, Bryan J Smith<b.j.smith@ieee.org>  wrote:
>> Yes, overlays often have issues with spanned framebuffers.
>>> The overlay often only works on the first framebuffer,
>>> although it may not work on either, depending on implementation.
>>
>>> Are you using Xinerama?  Or is the X driver doing the spanning?
>>
>
> Display from pull down menu, so I am pretty sure it is X.
>
>
>>
>> In a nutshell, anytime you use a hardware feature - overlay
>>> buffers (motion video), z-buffer (3D), etc..., it's not going work
>>> over Xinerama, possibly only one display or neither.  You must
>>> use an X driver that still supports these features when spanned
>>> across multiple screens.
>>
>>> Most X drivers use a single framebuffer for multiple screens
>>> to solve this issue, although it introduces other issues, because
>>> X doesn't know about the individual screens like it would with
>>> Xinerama.  Fortunately FreeDesktop standards have defined many
>>> settings/APIs so even single framebuffer X drivers can correctly
>>> communicate where individual displays start and end.
>>
>>> In-a-nutshell:
>>
>>> Unless I'm using a nVidia card, I don't span screens and expect
>>> overlay support.  For my T60, I mirror screens instead of
>>> spanning so they are the same framebuffer.
>
> Bad on me because I thought I broken something and rebuild the server. Good thing it was a new build w/o any configuration/tweaking.


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