[diagrams] diagrams status

[Scott N. Walck]

On Thu, Aug 12, 2010 at 11:48:26AM -0400, Brent Yorgey wrote:
> Hi all,
> 
> Here's an update on the current status of the diagrams project.
> Obviously things are sort of ground to a halt at the moment.  Partly
> that's due to me being busy with my internship at Microsoft Research.
> But partly it's because of a giant roadblock in the design of the
> project itself.
> 
> As you may already know, the main issue is the way our functional
> representation of convex bounding regions interacts with certain
> transformations.  In particular, we don't know how to correctly
> transform convex bounding regions under transformations that don't
> preserve angles (which includes shears, non-uniform scales, and pretty
> much all projective transformations).  I see three options:
> 
>   1) Buckle down and work really hard and figure out how to do it.
>      Pros: this would be awesome.  
>      Cons: we don't even know if it's possible.
> 
>   2) Only allow angle-preserving transformations.  
>      Pros: this option is simplest.
>      Cons: might be too restrictive.
> 
>   3) Switch to a different representation of bounding regions that
>      will integrate better with general transformations.
>      Pros: ability to do general transformations.
>      Cons: probably a lot of work, and the current representation
>      seems so elegant and functional, it would be a shame to give it
>      up.
> 

I could live without shears and projective transformations, but non-uniform
scaling seems a very basic and natural thing to want to do.
"I want this diagram to be the same height but twice as wide."
This is just the kind of thinking that makes the combinator-based
drawing approach so powerful.  I would give up three and higher dimensions
before I'd give up horizontal scaling.

Scott