[NTG-context] Re: Breakable tcolorbox in ConTeXt

[Hans Hagen via ntg-context <ntg-context@ntg.nl>]

On 8/11/2024 11:24 AM, Florent Michel wrote:
> Hi,
> 
> I am trying to reproduce the behaviour of the tcolorbox LaTeX package, 
> more specifically breakable boxes (as illustrated here: 
> https://tex.stackexchange.com/a/676607/123770 
> <https://tex.stackexchange.com/a/676607/123770>). It works nicely out of 
> the box (pun intended) using `\definetextbackground` and drawing the 
> frame with MetaPost, using counters to keep track of whether the current 
> text is at the top, middle, or bottom of the box. However, I'm having 
> issues when one box ends and another starts on the same page (see more 
> details below). From what I understand, the issue is that counters seem 
> to be updated on a page-wide basis, so each MPgraphic ‘sees’ the values 
> of counters at the end of the current page, which may not be right if 
> another box modifies them. Would anyone know how to resolve this?
> 
> Based on two answer on TeX StackExchange 
> (https://tex.stackexchange.com/a/486124/123770 
> <https://tex.stackexchange.com/a/486124/123770> , 
> https://tex.stackexchange.com/questions/377234/context-frame-problems/377261#377261 <https://tex.stackexchange.com/questions/377234/context-frame-problems/377261#377261>), the following code works well if there is no more than one box per page:
> 
> ```

You're missing a feature:

this is the original trick:

if     multilocs[i] == 1 :  % begin
elseif multilocs[i] == 2 :  % between
elseif multilocs[i] == 3 :  % end
fi ;

and in lmtx we have

if      multikind[i] = "single" :
elseif  multikind[i] = "first"  :
elseif  multikind[i] = "middle" :
elseif  multikind[i] = "last"   :

Also:

      path p;
       p := ( llcorner multipars[i]
              -- lrcorner multipars[i]
              -- urcorner multipars[i]
              -- ulcorner multipars[i]
              -- cycle )
              enlarged (EmWidth,EmWidth) ;
       fill p withcolor boxfillcolor ;

can be

fill multipars[i] enlarged (EmWidth,EmWidth) ...

Hans


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