[dev-context] \lastxpos and \lastypos should behave like registers

[Henri Menke]

On 23/05/19 11:55 AM, Hans Hagen wrote:
> On 5/23/2019 1:47 AM, Henri Menke wrote:
>>
>>
>> On 23/05/19 11:36 AM, Hans Hagen wrote:
>>> On 5/23/2019 1:11 AM, Henri Menke wrote:
>>>> Dear devs,
>>>>
>>>> The two macros \lastxpos and \lastypos should behave like registers,
>>>> because that is what they are in LuaTeX.  The following MWE fails with
>>>>
>>>> ! You can't use `the character 0' after \the
>>>>
>>>> \starttext
>>>> \the\lastxpos
>>>> \the\lastypos
>>>> \stoptext
>>>>
>>>> A simple fix would be to wrap the macro in \numexpr like in the attached
>>>> patch.
>>>
>>> hm, i was actually about to drop them completely ... anyway, i have no
>>> problem with the fix but then it also need to be \unexpanded
>>>    (i'm reshuffling some code so probably no beta for a few days)
>>
>> Dropping \pdflastxpos and \pdflastypos would break TikZ, so it would be
>> good if at least the \lastxpos and \lastypos primitives would be
>> accessible.
> ok, but i assume that there is no need for the \pdf* ones (because i 
> decided to drop all those specific \pdf* aliases in the next beta ... 
> they were never meant to be persistent part of mkiv) ... i grepped tikz 
> and could not find usage of \pdf... apart from the official luatex ones
> 
> (actually, tikz is the only package i know that we need to keep an eye 
> on wrt downward compatibility; context modules use different interfaces)

You might be happy to hear that I am the current TikZ maintainer, so I
can shape it for best interoperability with ConTeXt.

Currently \pdflastpos is only used in one place
https://github.com/pgf-tikz/pgf/blob/07959624c5e4c50f80ddf31a3b271885237b37cc/tex/generic/pgf/systemlayer/pgfsys-common-pdf-via-dvi.def#L97-L102
but that can be abstracted.

Cheers, Henri

> 
> Hans
> 
> 
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