On Wed, 2012-10-31 at 08:47 -0400, m. allan noah wrote: > >> If you change the stuff, do you mind also changing the option-type of > >> button-1/-2 to SANE_TYPE_BUTTON (it is actually SANE_TYPE_INT)? > >> > > I am still looking at this. For now I have been able to wrap my brain > > around how to read a button option. Do I understand you correctly that a > > get operation on a button returns an integer. The documentation does > > only state that a button has no value. I see that some backends do > > return a value for type button, others don't. GIven the docuemntation I > > am not sure. I will wait for others to comment before I make changes > > (they would be fairly simple). > > > >> Is anyone aware of similar operation (setting one option for querying > >> another) in other backends (in that case I would consider updating > >> scanbd to suppport such a schema as well)? > >> > > For the pixma backend they are not required anymore.... > > > > > > kind regards, Louis > > > > Sounds like a good change. Unfortunately, the sane standard is a > little weak on buttons, so backend authors have to guess. I would say > that button/event reading code should not expect the type to be > SANE_TYPE_BUTTON, as some sensors will be able to give integer values. > > allan Hello all, Strictly speaking accoding to the sane abi doc (sane.ps) buttons do not have a value (Page 20: An option of this type has no value. Instead, setting an option of this type has an option-specific side effect. Page 21: SANE_TYPE_BUTTON, SANE_TYPE_GROUP: the option size is ignored
If a BUTTON can RETURN a value, we need to correct both places: P20 only talks about SETTING a value, but does not discuss GETTING the button, but P21 seems to suggest that reading is pointless. to me this looks as if the button-type is only meant to SET a (boolean) option and never can be read. But then it has only a subset of characteristics of the BOOL type (it is actually a boolean with implicit encoding: leaving it out indicates a false, sending the option, but no value, means a true, yes I come from a background where ASN.1 is used). To me it still looks as if a boolean or integer encoding are most appropriate. So I prefer to leave the buttons as integers (although they are now strictly speaking booleans, as I moved the original and target parameters to own options Comments? Kind regards, Louis