Re: DirectFB without FBDev

[Denis Oliver Kropp <dok@directfb.org>]

Geert Uytterhoeven wrote:
> On Wed, 28 May 2008, Denis Oliver Kropp wrote:
>> Geert Uytterhoeven wrote:
>>> On Wed, 28 May 2008, Denis Oliver Kropp wrote:
>>>> One major bug at the moment is mode switching and pitch values being
>>>> wrong. It's dumb to
>>>> return the pitch of the variable mode settings in the fixed settings
>>>> structure anyhow, but
>>>> if you like to start with the above mentioned mission, that's where it
>>>> could begin.
>>> Do you care to tell us why this is dumb?
>> Ok, the fixed information should not contain information that changes over
>> time,
>> otherwise it is not fixed, at least that's my understanding of "fixed".
> 
> It's `fixed' not in the sense that it can never change, but that it
> purely depends on the info in struct fb_var_screeninfo.

I'd prefer an ioctl which has input and output fields in the accompanied struct,
so that the resulting pitch is returned to the user space with the same system call.

>>> The pitch depends on the video mode and the hardware requirements,
>>> that's why it's in struct fb_fix_screeninfo.
>> It would suffice to encode the pitch requirements independent from the video
>> mode,
>> i.e. just put the pixel or byte alignment into the fixed structure.
> 
> What if the pitch requirements depend on the video mode?

Haven't seen that, usually either pixels or bytes just needs to be a multiple
of something. In these cases you could simply forbid/fail to choose the pitch and
just return it in the variable structure.

> There exists graphics hardware where fb_fix_screeninfo.type depends on
> the video mode.

Sure, type depends on the pixelformat :)

-- 
Best regards,
   Denis Oliver Kropp

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