constraints (was: web browsers)

karl karl.ramberg at chello.se
Sat Apr 23 07:00:03 UTC 2005


Jecel Assumpcao Jr wrote:

>Ned Konz wrote on Fri, 22 Apr 2005 12:02:51 -0700
>  
>
>>John Maloney certainly has the background to answer that, having done a couple 
>>of papers (and his PhD thesis?) on constraint systems for GUIs.
>>    
>>
>
>Thanks for the book chapter reference! While looking for that I found
>other interesting things, including a paper about Cassowary which is
>available on the SqueakMap.
>
>  
>
>>I'm sure he can give more information on this, but when we talked about 
>>general-purpose constraint systems for Squeak GUIs I got the impression that 
>>he felt that the difficulty of communicating to the user just what was (or 
>>wasn't) happening in the constraint system would get in the way of general 
>>usefulness.
>>    
>>
>
>Interesting - the reason I wanted something like this was the idea that
>constraints could be represented graphically in a way that would be easy
>for the user to keep track of what was happening. We could have a set of
>scaffolding objects whose visibility could be turned on or off as
>needed.
>
>  
>
>>My impression has been that non-rigorous constraint systems (i.e. ones that 
>>don't require all of their constraints to be satisfied all of the time) may 
>>be helpful with GUI construction.
>>    
>>
>
>The Cassowary paper talked about several levels of constraint priorities
>(or strengths) with the lowest ones being ignored as needed.
>
>  
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>>However, we haven't fully attacked the simplest of layout schemes yet.
>>    
>>
>
>Tables are the case I am interested in. They actually aren't
>complicated, but do need constraints in both X and Y directions at the
>same time.
>  
>
The SGGrid package I used in the TableMorph is quite good and simple. 
But you have to
do a lot of hinting and checking to get width and height anywere near 
good looking and help it with column and row spans. I do several things 
to get it right, but there are many variation and issues.
I think any framework would need a lot of hinting and massage to layout 
a HTML table in a nice
way.
Karl

>  
>
>>For instance, the GTK+ scheme that uses horizontal or vertical containers with 
>>different kinds of glue between their contents is at least easy to program 
>>and explain.
>>    
>>
>
>This sounds similar to TeX and Morphic. It is nice to try to avoid
>invisible objects in a layout scheme, but you often end up using a space
>filling rectangle with the exact same color as the background to get
>what you want and the effect might end up being very similar in
>practice.
>
>-- Jecel
>
>
>
>  
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