[luatex] CJK vertical typesetting

[Hartmut Henkel]

> The problem seems to occur because of the strange behavior
> of boxes under RTT dir.  Take a look at the following code;
> is this intended behavior?
> 
> \pagedir RTT \bodydir RTT
> \offinterlineskip
> \setbox0=\hbox{} \ht0=5pt \dp0=5pt
> \setbox2=\vbox{\copy0\box0}
> \showthe\ht2 \showthe\dp2 % prints 15pt, 5pt  (ok)
> \setbox4=\hbox{\box2}
> \showthe\ht4 \showthe\dp4 % prints 10pt, 10pt (??)
> \bye

it's so by design,the \vbox is "vertically" centered around the baseline of the enclosing \hbox.

Luatex inherited this behavior (no idea, if this really is a good thing, the (ht + dp) / 2 shift adjustment in the code looks a bit arbitrary imho, and there hasn't been much RTT activity yet). 

Regards, Hartmut
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