[luatex] math display box structure

[David Carlisle]

On 15 March 2016 at 10:11, Hans Hagen <pragma at wxs.nl> wrote:
> On 3/15/2016 10:50 AM, David Carlisle wrote:
>
>> The output here is using 8bit cm fonts so I'm not sure how opentype is
>> relevant.
>
>
> Well, I assume that when you talk about comparable output you mean all kinds
> of math output and then fonts come into play. So, they are relevant in the
> sense that in order to support both, we have some places in the code where
> there code paths meet (unless we completely split math engines: old
> untouched vs new, adapted). So, if we can share bit of code (i didn't check
> the details) by replacing a shift by a kern (or whatever) so be it.
> Basically what happened was that the new code (already from years ago) was
> kind of guessing what solution was needed for what font, and that in the end
> became too fragile which then was changed into different code paths but not
> going back to old code, also because we have more parameters to deal with).
> So, even for 8 bit fonts and the old approach code path there can be
> differences. So ... maybe more wrapping (extra boxes) or different spacing
> models (kerns vs shifts).
>
> I assume that when you talk about classical tex output you refer to e.g.
> pdftex but maybe i misunderstand. Luatex will not be compatible at that
> level, also because for instance in the eqno case you mention related code
> has to deal with right to left math / numbers / placement and mixed cases
> and that gets reflected in how boxes come out. So again we don't aim at (or
> even care about) compatible output at the box level.
>
>
> Hans
>

It is useful to be able to get the same (or at least mechanically transformable)
log output as that helps in generating test files from existing test
files for other engines,
but note I did not ask for that, mainly I asked for any documentation of
what the output is supposed to be.

How is it possible to test a system if there are no test files and no
specification of the behaviour?

Recent releases have shown that you _really_ need such test files.

David