Ralph Little writes:
> Hi, > > On 2020-03-07 6:06 p.m., Olaf Meeuwissen wrote: >> # I considered adding a polling loop but that doesn't make much sense. >> # You can only signal the frontend via sane_control_option() that it >> # needs to SANE_INFO_RELOAD_OPTIONS, so checking there is good enough. > > I had a look at this. > I don't think this really helps me here. > A polling loop is the only real way for this to work. I know but the SANE Standard does not provide any way to forward the result of that polling loop to a frontend in a timely fashion :-/ There zero notification support. Way back when some of the SANE developers were working on the draft for Version 2 of the SANE Standard they realised so much and added a TODO[1] for a SANE_CAP_AUTO_POLL capability. The draft has been in "coma" since Autumn 2003 ... and that capability was not added. [1] http://sane-project.org/sane2/sane2-todo.html BTW, the above URL is slated for removal. I still have to turn what's left (and relevant) into issues :-| > xsane could do this for some options that were marked in a way to make > it obvious that it should do it. Perhaps we should consider blowing the dust of that draft ... > In the Windows utility, pressing the scanner buttons does immediately > reflect the change in the settings dialog so that they are kept in sync. > It might be that we could enhance xsane to poll sensors so that they > reflect in realtime what is being set on the hardware. > That could be easily done with an object timer I suspect, but I will > defer that for the moment. I would prefer some kind of backend-to-frontend notification mechanism (pub-sub?) over polling but it should be made part of the SANE Standard so that all frontends can benefit from it. Hope this helps, -- Olaf Meeuwissen, LPIC-2 FSF Associate Member since 2004-01-27 GnuPG key: F84A2DD9/B3C0 2F47 EA19 64F4 9F13 F43E B8A4 A88A F84A 2DD9 Support Free Software https://my.fsf.org/donate Join the Free Software Foundation https://my.fsf.org/join
