[luatex] math display box structure

[Hans Hagen]

On 3/14/2016 9:59 PM, David Carlisle wrote:
> Hi,
>
> luatex constructs boxes for display math differently to classic tex,
> typically adding kerns rather than shifting.
>
> In simple cases it makes the same visual output but it is easy to find
> cases where the typeset output is different
>
>
> \setbox0\vbox{$$ x \eqno (1)$$
> \par
> \unskip
> \unpenalty
> \global\setbox1\lastbox}
>
> \the\wd1
>
> \box1
>
> \bye
>
>
> However even when the typeset output looks the same the fact that the
> box log is so different makes regression testing quite hard. The
> recent bug reports about \choose
> and \thinmuskip only came to light after manually filtering out
> hundreds of lines of box differences due to the different box
> constructs.
>
> Accepted that luatex logging is never exactly the same as pdftex's, is
> there a particular new functionality that is gained by these changes,
> or failing that is there any documentation (other than the luatex
> source code) of the expected places where the box structure for
> mathematics will be different, so that we can try to automate
> filtering out these differences for regression testing?

the code paths for traditional tex and opentype math tex are different 
because the models are slightly different (things like italic correction 
and such are completely different which demands different code paths; 
also we have some extensions that demand a bit different approach)

as a consequence there are also possible differences between the 
rendered math and we don't aim at them being compatible (8 bit font 
based vs wide fonts)

in fact, probably after 1.0 i will experiment a hit with even less shift 
based in the opentype code path simply because it is a bit messy when in 
a viewer one selects (e.g for cut/paste) and so because there is much 
lying about dimensions that way

(in a similar fashion one cannot expect 8 bit font handling e.g. with 
ligatures to be compatible with opentype solutions)

so the answer is: no, they will not be made the same and might even 
divert more (and don't expect 8 bit font output to be the same as their 
opentype successors)

Hans

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                                           Hans Hagen | PRAGMA ADE
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