[luatex] Bad skips with display math

[Hans Hagen]

On 1/12/2022 7:00 PM, Javier Bezos wrote:
> Hello,
> 
> Consider the following document, typeset with 1.13.2 (TeX Live 
> 2021/W32TeX):
> 
> ==================================
> 
> Lorem ipsum dolor sit amet, consectetur adipiscing elit,
> sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
> $$(a+b)^2 = a^2+2ab+b^2 \eqno (1.10)$$
> Lorem ipsum dolor sit amet, consectetur adipiscing elit,
> sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
> $$(a+b)^2 = a^2+2ab+b^2 \leqno (1.10)$$
> Lorem ipsum dolor sit amet, consectetur adipiscing elit,
> sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
> 
> \textdir TRT \pardir TRT \bodydir TRT \pagedir TRT
> 
> Lorem ipsum dolor sit amet, consectetur adipiscing elit,
> sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
> $$(a+b)^2 = a^2+2ab+b^2 \eqno (1.10)$$
> Lorem ipsum dolor sit amet, consectetur adipiscing elit,
> sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
> $$(a+b)^2 = a^2+2ab+b^2 \leqno (1.10)$$
> Lorem ipsum dolor sit amet, consectetur adipiscing elit,
> sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
> 
> \bye

\predisplaydirection=0 might help here (defaults to -1)

that code is very unlikely to be changed (already tricky enough)

> ===================================
> 
> The result is http://www.texnia.com/archive/luamathskip.pdf
> 
> As you can see, the labels are reversed, but the calculations for
> the vertical skips, based on the previous line, are not. Either
> the labels shouldn’t be reversed (which makes sense for me,
> because conceptually we are in math and not in a paragraph) or
> the calculations have to be fixed.
> 
> Please, fix also the long standing bug which misplaces the label
> with leqno when \pardir (but no other dirs) is set to TRT.
I'll look into it (in luatex maybe under some flag/mode control because 
we are frozen).

Hans

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------