Roel,

Thanks this is helpful information. Yes, I _really_ want to have
constraint violations be noticable since otherwise the user won't be
able to react to them (if only by removing the last constraint - I
really don't care; the important part is to give feedback that "this
won't work"). BTW, what constraint solver did you end up using?!

Cheers,
  - Andreas

> -----Original Message-----
> From: Roel Wuyts [mailto:roel.wuyts at iam.unibe.ch] 
> Sent: Friday, January 10, 2003 5:09 PM
> To: Andreas Raab
> Cc: squeak-dev lists.squeakfou
> Subject: Re: Cassowary anyone?!
> 
> 
> I used Cassowary for checking/finding task schedules. In the end I 
> chose another solver (not in Smalltalk) exactly for the reasons you 
> mentioned: constraint violations are not shown, so it is hard to see 
> what exactly is going on. Sometimes a constraint is preferred over 
> another one (of the same priority) for a reason which is not clear. 
> Then you end up with a network in which one constraint is satisfied, 
> and another one of the same priority is not. In the application for 
> which I wanted to use Cassowary this was not acceptable. Note that if 
> the constraint is 'required' (the highest setting), then such a 
> situation cannot rise: if it cannot be satisfied, an exception is 
> thrown. So I ended up using Cassowary as though it had no constraint 
> hierarchies at all... and then I could better use another 
> solver. With 
> a bit of more time I would have looked at it (I implemented a 
> constraint solver before on top of Soul), but time is absolutely a 
> scarce resource at the moment.
> 
> PS: I noticed that this mail is not very clear, depending on your 
> knowledge of Cassowary. Just contact me for more info or the code of 
> the experiments I did.
> 
> On Thursday, January 9, 2003, at 08:11 PM, Andreas Raab wrote:
> 
> > Josh,
> >
> > Thanks - by now I got various copies from people (thanks to all of 
> > you!)
> > but this is the kind of thing that really _ought_ to be on SqueakMap
> > (hint, hint!).
> >
> >> What are you thinking of doing with it?
> >
> > I'm looking into different ways of end-user friendly 
> specification of
> > "object compositions" (aka: layouts). Since I know that 
> Cassowary was
> > used for CSVG and other things I was wondering if it might be a good
> > starting base for some more end-user friendly model than we 
> have right
> > now.
> >
> > This problem bugged me for a long time now - the AlignmentMorph's in
> > Squeak used to require compositions of compositions of 
> compositions of
> > nested things and they just got in the way of "seeing the 
> thing you are
> > interested in" (namely some object of the composition). So 
> I tried to
> > generalize this into the layouts we have today but while 
> they are more
> > general they are also much harder to understand (lots of 
> very generic
> > properties with lots of unclear compositional effects).
> >
> > So what I am essentially looking for is some way of 
> specifying "lots of
> > dog-simple constraints" (like: make the left edge of one 
> guy follow the
> > right edge of some other guy) and provide some interactive means for
> > specifying it - so that rather than having a set of generic 
> properties
> > the user gets a (possibly large) number of very concrete
> > mini-constraints. Those need to be solved efficiently and 
> that's when I
> > got into thinking about the various constraint solvers.
> >
> > BTW, do you know if Cassowary can give feedback about 
> constraints that
> > cannot be resolved (perhaps even potentially)?! I'm 
> interested in this
> > because what I would like to do is give constant feedback about the
> > composition you are building - so that when you add a 
> constraint which
> > "won't work" the system could indicate this by some means.
> >
> > Cheers,
> >   - Andreas
> >
> >> -----Original Message-----
> >> From: squeak-dev-admin at lists.squeakfoundation.org
> >> [mailto:squeak-dev-admin at lists.squeakfoundation.org] On
> >> Behalf Of Joshua 'Schwa' Gargus
> >> Sent: Thursday, January 09, 2003 7:32 PM
> >> To: Andreas Raab; Squeak Mailing List
> >> Subject: Re: Cassowary anyone?!
> >>
> >>
> >> Hi Andreas,
> >>
> >> My message to the list seems to have been lost, so I'm resending
> >> to you and the list.
> >>
> >> You can get Cassowary from:
> >> http://www.cc.gatech.edu/~schwa/squeak/packages/
> >>
> >> What are you thinking of doing with it?
> >> Joshua
> >>
> >
> >
> Roel Wuyts                                                   Software 
> Composition Group
> roel.wuyts at iam.unibe.ch                       University of Bern, 
> Switzerland
> http://www.iam.unibe.ch/~wuyts/
> Board Member of the European Smalltalk User Group: www.esug.org
>