[sane-devel] Sane API

Alexander Pevzner pzz at apevzner.com
Tue Oct 20 09:12:03 BST 2020

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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