[sane-devel] Sane API

Jürgen Mellinger juergen.mellinger at t-online.de
Tue Oct 20 17:40:42 BST 2020

Hi Alexander,

I would like to add "mssing option to poll ADF state" to what is missing from the current API.
With the current API, it is not possible to prompt the user with meaningful messages such as "please put a document into the ADF" vs "there is a paper jam in the ADF" and similar.


> Am 20.10.2020 um 10:12 schrieb Alexander Pevzner <pzz at apevzner.com>:
> Hi Thierry,
> On 10/20/20 9:50 AM, Thierry HUCHARD wrote:
>> I went to quickly look at sane-2.0: - I agree with @paddy-hack,
>> making new with old is not necessarily a good thing! - I found that
>> the difference was in the options. The operations are identical. It
>> will be easy for a developer to create a gateway from sane-1.0 to
>> sane-2.0. - The options are hardware dependent and there, some
>> options are emulatable, others are not. - If sane-2.0 is just the
>> formatting of the options, why not do it in sane-1.0?
> Current API misses some essential things, that cannot be implemented in terms of options:
> - PnP notifications (scanner was connected/disconnected some time after
> driver was initialized). This limitation can be worked around by
> continuous poll, but this poll drains a battery a generates network/USB
> traffic, so it is better to avoid.
> - If some scanner is identified by multiple backends, it would be nice
> to let user app to automatically choose one of the list. For this
> purpose, it would be nice to expose some information regarding scanner
> location, before scanner is opened (say, "USB bus X device Y, or NET
> addr aaa.bbb.ccc.ddd). It requires adding extra fields to the
> SANE_Device structure, which makes it incompatible with SANE 1.0
> For the following things we just don't have appropriate SANE_Value_Type:
> - Scanner resolution if a form of X*Y pair. This is important, to
> support "asymmetrical" resolutions (300*600, for example)
> For the following options we don't have enough discipline:
> - SANE_NAME_SCAN_SOURCE. There is no common names for ADF simplex/ADF duplex, ADF front/ADF back
> sane_airscan_get_parameters() must be accurate immediately after return from sane_start(). It is not always possible, unless sane_start() has to wait until image is available (compare sane-escl and sane-airscan approach).
> sane_airscan_get_select_fd() defined with serious mistake: it requires backend to close select_fd immediately after completion or cancellation of the scan job. In multi-threaded program closed file descriptor could be immediately reused for some different purpose by another thread.
> There is no possibility to request image in the device-specific "raw" format. I.e., if I want PDF and device can return PDF, image still will be repacked PDF->sane format->PDF.
> My list is most likely very incomplete.
> -- 
> 	Wishes, Alexander Pevzner (pzz at apevzner.com)

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