[plt-scheme] Layout and grids with MrEd?

From: Danny Yoo (dyoo at hkn.eecs.berkeley.edu)
Date: Fri Apr 21 19:29:44 EDT 2006

Hi everyone,

I'm starting to write a tutorial on MrEd.  (My motivating way to learn 
something new is to try to explain it).

But I'm running into some awkward code that I want to fix before posting 
this to the Schematics Cookbook.  It involves writing a grid% class to 
practice with simple geometry management:

   (define simple-grid%
     (class object%
       (init parent)
       (init [columns-per-row 3])

       (define -columns-per-row columns-per-row)
       (define main-panel (new vertical-panel%
                               [parent parent]))

       (define current-column-position (void))
       (define current-row-panel (void))

       (define (make-new-row!)
         (set! current-row-panel
               (new horizontal-panel%
                    [parent main-panel]
                    [alignment '(center center)]))
         (set! current-column-position 0))


       (define/public (with-parent f)
         (cond [(= current-column-position -columns-per-row)
                (with-parent f)]
                (f current-row-panel)
                (set! current-column-position
                     (add1 current-column-position))]))))

The problem with it is that this grid% is not really a peer with the other 
layout containers (horizontal-panel%, vertical-panel%), and rather than 
writing the ideal code:

     (define a-frame (new frame% [label ""]))
     (define a-grid (new simple-grid% [parent a-frame]))
       (lambda (msg)
         (new message% [label msg] [parent a-grid]))
       '("this" "is" "a" "test" "hi" "mom"))

I'm instead writing:

     (define a-frame (new frame% [label ""]))
     (define a-grid (new simple-grid% [parent a-frame]))
       (lambda (msg)
         (send a-grid with-parent
               (lambda (p) (new message% [label msg] [parent p]))))
       '("this" "is" "a" "test" "hi" "mom"))

I'm trying to compose panels together, but the result isn't observing the 
closure property I want.

I've been reading through the MrEd documentation to see what I can do to 
make *simple-grid%* a real container, and I suppose I should just bite the 
bullet, inherit from *panel%*, and write *container-size* and 
*place-children* methods as described in:


I was wondering if there were anything else I could do to reuse the 
functionality that *horizontal-panel%* and *vertical-panel%* provide, or 
if I'll have to just recode their logic.

Just in case people are interested in really rough drafts, here's what 
I've written so far on a MrEd tutorial:


I'm not linking it to my main site yet because they are in a really rough 
state right now; I'm still fumbling toward proficiency.

Hope this helps!

Posted on the users mailing list.