Re: Blank page added after pagecolumns

[Wolfgang Schuster <wolfgang.schuster.lists@gmail.com>]

Joey McCollum schrieb am 16.05.2020 um 05:45:
> All right, I've found a tentative solution that appears to work in all 
> cases, but I'd like to know more about why the code I'm patching was 
> implemented in the first place, because I don't want to break anything 
> else. According to the code in page-pcl.mkiv, the \stoppagecolumns macro 
> has two implementations, \page_col_stop_yes and \page_col_stop_nop. The 
> choice of which implementation is used is determined by which of two 
> implementations of \startpagecolumns (\page_col_start_yes 
> and \page_col_start_nop) is used. That choice, in turn, is made in 
> the \page_col_start macro, in the following lines:
> 
> ```
> \c_page_col_n_of_columns\pagecolumnsparameter\c!n\relax
>     \ifnum\c_page_col_n_of_columns>\plusone
>       \expandafter\page_col_start_yes
>     \else
>       \expandafter\page_col_start_nop
>     \fi
> ```
> 
> so if the number of columns (i.e., the n option for the 
> pagecolumns environment) is more than one, the "yes" implementation of 
> the start and stop commands is used.
> 
> But this seems wrong. The naming convention for the two implementations 
> ("yes" and "nop") suggests that they should be related the parameters 
> "page=yes" and "page=no" (hence, no page, which is what I think "nop" 
> abbreviates), but the choice of which implementation to use is 
> determined not by the page parameter, but by the n parameter. Is this an 
> error in the code, or am I just understanding this incorrectly? Is there 
> some reason why a layout with more than one column would need special 
> instructions to add a blank page after stopping the environment?

Why do you think "yes" and "nop" are related to the page-key?

> In any event, I was able to solve the problem by patching the 
> \page_col_start_yes macro to invoke the \page_col_start_nop macro as 
> follows:
> 
> ```
> 
> \unprotect
> 
> \def\page_col_stop_yes
> {\page_col_stop_nop}
> 
> \protect
> 
> ```
> 
> With this fix, the MWE I provided works regardless of which column the 
> text ends in. I'm content to consider the problem solved, but I would 
> certainly appreciate any feedback on my thoughts and questions about 
> page-pcl.mkiv.

You broke now now normal single columns text after the pagecolumns 
environment. A better fix is to add a check for the \column command at 
the end of the environment and add it only when we aren't in the last 
column.

\unexpanded\def\page_col_stop_yes
   {%\column % \page_otr_eject_page
    \ifnum\c_page_col_current<\c_page_col_n_of_columns
      \column
    \fi
    \page
    \endgroup
  % \setupoutputroutine[\s!singlecolumn]%
    \page_otr_command_set_vsize
    \page_otr_command_set_hsize
    \page
    \endgroup}

Wolfgang
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