Re: [NTG-context] underbraces get progressively more misaligned (w/ minimal example)

On 7/4/2014 11:34 AM, Sanjoy Mahajan wrote:

Wolfgang Schuster writes:

...

It does also depend on the width of the text because when I use 48pt in the example below the height of the brace is always the same but with 49pt the height increases after the first page.

An interesting bug. That's also consistent with my experiments, in which

\underbrace{\hbox{yyyy yyyy}}_{\rho}

triggers the problem, but

\underbrace{\hbox{yyyy}}_{\rho}

does not.

Hi Sanjoy, After a day of testing, tracing, wondering etc Luigi and I figured out what was the problem it tooks us lots of debug prints -). Indeed there is a bug in luatex. An extensible is made up of a sequence char skip 0pt- xpt char skip 0pt- xpt char skip 0pt- xpt char And the code that determines the height/depth took the dimensions of skips into the equation while in fact glue has no such dimensions (leaders that are a special kind of glue have dimensions). Not the first place one looks for such an issue. Probably a side effect of copying a function and patching part. So, some random value (not entirely random as it depends on what mem area the glue node is allocated from and that is kind of stable in a run) was added which results in the effects you noticed. Because it is stable within a run (same successive errors) it doesn't result in oscillating (too many runs due to differences in results) and this is probably why it went unnoticed so long. Interesting. (Normally the pseudo random ht/dp were small.) So, once this fix moves upstream you can check your suspicious cases. Luigi will push it in our experimental branch and I suppose that Taco will then push it into trunk and after that you can compile or wait till the garden carries it. Thanks for noticing! Hans ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | voip: 087 875 68 74 | www.pragma-ade.com | www.pragma-pod.nl -----------------------------------------------------------------