[sane-devel] SANE 1.1.0 Release discussion

[René Rebe]

Hi,

ps: this time to the list as well :-)

m. allan noah wrote:
> On 5/26/08, René Rebe <rene at exactcode.de> wrote:
>> Hi Allan,
>>
>>  can you explain the paper width option to me? Why can we
>>  not simply use br x/y?
>>
>>  Actually I got a Fujitsu scanner here and find the duplicate
>>  paper width option annoying at best.
> 
> it is not duplicate. it is used by the backend to properly center the
> users x/y params to the moving paper guides. otherwise, if they want
> to scan an entire sheet of A5, they have to set the tl_x/y to some
> weird value that they have to calculate from the scanner's maximum
> width.
> how do you handle this in avision now?

not at all, I consider this a front end job, it also avoids the simple
arithmetic in every backend. The page size then also appears to indirectly
change the maximal scan area? I find this way more "complex" than just allow
frontends to center the scan area on the maximal area.

>>  Aside the already mentioned button to use some more extend-able
>>  XML encoding instead of a hardcoded set, I wonder if it is
>>  good to expose sensors, frontends would rarely (if ever?) want
>>  to check for them explicitly and the backend must check the
>>  sensors before or during scan to generate proper errors
>>  accordingly anyway.
> 
> don't assume that sensors only indicate errors. the paper-in signal is
> quite useful in high volume apps- the front-end can start scanning
> immediately.

Ah ok, media presense is indeed useful, granted. One could also
start scaning on cover close, indeed. I was just afraid on exposing
random sensors (home, etc.) without a real need.

> xml does not fix this problem, cause we would still have to define a
> schema so that front-ends could interpret it. so, lets just avoid the
> xml dependency.

Still, many Avisions have Simplex / Duplex buttons, and some, like the
HP 7400, allow resolution, color mode, and number of copies to be
set on the device. How would you like to handle those then (and yes,
the Avision backend does not export the 7400 options, yet, as I had
no idea, beside a pre-formated  string message, how to expose them)?

The problem with letting some buttons change the backend internal
state configuration (resolution et al.) and some be exposed to the
frontend (scan, fax, print) exposes two problems: One the frontend
UI (if any) does not update when the user changes scanner values,
and second may yield to scans with other parameters than the frontend
believed to scan with. Having one flow of hardware "notifications"
might be more structured and frontend friendly.

Yours,

-- 
   René Rebe - ExactCODE GmbH - Europe, Germany, Berlin
   http://exactcode.de | http://t2-project.org | http://rene.rebe.name