Re: a way to implement \testcolumn in mixedcolumns

[Hans Hagen <pragma@wxs.nl>]

On 11/20/2013 10:47 PM, Lars Huttar wrote:
> Hello,
>
> On this list I've been advised that mixedcolumns is the latest and
> greatest implementation of columns; the one to use. We have switched
> over from columnsets to mixedcolumns, and have been very pleased with
> the column balancing (for some reason we couldn't get column balancing
> to work in columnsets).
>
> However one thing we do miss from columnsets is the control over widows
> & orphans in two ways: \testcolumn, and \setupcolumnsetlines.
> \testcolumn[n] allowed us to do a conditional column break, so when we
> were about to start a new subsection heading, we could prevent it being
> an orphan at the bottom of the column; and when starting a paragraph
> with a hangaround graphic framed flushright and bottom, we could
> similarly use \testcolumn to prevent the graphic from hanging down into
> the footer (which is what sometimes happened otherwise).
>
> So I'm wondering, is there some way to achieve the equivalent of
> \testcolumn in mixedcolumns?
>
> Is it theoretically impossible to implement this in mixedcolumns because
> the required information (how many lines are left in the current column)
> is not yet known?
> Or could that information be gleaned from somewhere?
>
> I see in page-brk.mkiv the following definition for \testcolumn:
>
> \def\testcolumn
>    {\dodoubleempty\page_tests_columns_test}
>
> \def\page_tests_columns_test[#1][#2]%
>    {\endgraf
>     \ifdim\pagegoal<\maxdimen
>       \ifdim\pagetotal<\pagegoal
>         \d_page_tests_test\dimexpr
>           \pagegoal
>          -\pagetotal
>           \ifdim\lastskip<\parskip+\parskip\fi
>           \ifsecondargument+#2\fi
>         \relax
>         \getrawnoflines\d_page_tests_test % (raw)
>         \ifnum#1>\noflines
>           \column
>         \fi
>       \else
>         \penalty-\plustenthousand % (untested)
>       \fi
>     \fi}
>
>
> I'm not a low-level TeX programmer, and I don't understand a lot of
> this, but it looks like
>    \getrawnoflines\d_page_tests_test
> puts the number of remaining lines into \noflines
>
> Any suggestions are appreciated.
> (And I should have a MWE soon.)

That macro was never meant for mixed columns. I made a variant that 
works ok in mixed columns which will be in the next beta.

\setuptolerance[verytolerant]

\starttext

\startmixedcolumns

     \dorecurse{4}{\input ward \par}

     \testcolumn[10][-1pt] % 10 lines - 1pt slack

     \dorecurse{2}{\input ward \par}

\stopmixedcolumns

\stoptext




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