No progress event during the scan process when using the sane-airscan backend

[Claus Dietrich <claus.dietrich@xxxxxxxxxx>]

My Gambas scanner app used to work without issues since years:

https://www.gambas-club.de/viewtopic.php?t=5954

Since I upgraded to Mint 22 I have the problem, that the scan progress 
is not displayed any longer.

As I found out, Mint 22 is now using the sane-airscan backend 
additionally to the sane-utils backend. As a result my app now lists two 
scanner devices although only one is connected and the 
sane-airscan-option was selected as default. It is OK for me to have the 
choice between two scan-devices (resp. backends) now and the 
sane-airscan backend also provides a perfect scan. But when it is 
selected my app doesn't displays the scan progress in its progress-bar 
any longer.

It turned out the "progress" event of the scanner class is not fired 
during the scan progress when using the sane-airscan backend. Instead it 
seems that the events are "collected" and in order to catch up it fires 
all "collected" progress events at the end of the scan process in a 
single batch and within a very short time.

As far as I remember the progress event also used to fire during the 
scan process, when using the sane-airscan backend. Do we possibly have a 
new bug?

When I select the scanner device working with the sane-utils backend 
everything is still fine.

Please be aware that my app uses the scanner class as source code with a 
number of modifications, but non of them are relating to events.

Best regards, Claus