Re: [sane-devel] Sane API

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From: Alexander Pevzner
Sent: Tuesday, October 20, 2020 1:12 AM
To: [email protected]
Subject: Re: [sane-devel] Sane API

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 ([email protected])

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