[metapost] btex..etex debugging

[Laurent Méhats]

Le 13/03/2013 08:42, Stefan Witzel a écrit :
> Hi,
>
> this is just a remark, as I said, I'm not really interested in the
> bbox makro in this contex. However, I just noticed that the
> documentation mpman.pdf (as of October 26, 2010) states that:
>
> "If p is a picture, bbox p is equivalent to (llcorner p--lrcorner
> p--urcorner p--ulcorner p--cycle)."
>
> (page 27). So this is then just false, is it?
>
> Best,
> Stefan

Hello,

Actually, according to the manual, "If p is a picture, bbox p is 
equivalent to (llcorner p--lrcorner p--urcorner p--ulcorner p--cycle)", 
indeed, "except that it allows for a small amount of extra space around p 
as specified by the internal variable bboxmargin." So 'bbox p' is in fact 
equivalent to:
   llcorner pct shifted (-bboxmargin, -bboxmargin)--
   lrcorner pct shifted (+bboxmargin, -bboxmargin)--
   urcorner pct shifted (+bboxmargin, +bboxmargin)--
   ulcorner pct shifted (-bboxmargin, +bboxmargin)--
   cycle

Also, "Note that MetaPost computes the bounding box of a btex ... etex 
picture just the way TEX does. This is quite natural, but it has certain 
implications in view of the fact that TEX has features like \strut and 
\rlap that allow TEX users to lie about the dimensions of a box. [...] To 
get the true bounding box of such a picture, assign a positive value to 
the internal variable truecorners" Here is an example:

--%<-- test.mp
verbatimtex%&latex
\documentclass{article}
\begin{document}
etex

vardef auxbbox expr pct=
   llcorner pct shifted (-bboxmargin, -bboxmargin)--
   lrcorner pct shifted (+bboxmargin, -bboxmargin)--
   urcorner pct shifted (+bboxmargin, +bboxmargin)--
   ulcorner pct shifted (-bboxmargin, +bboxmargin)--
   cycle
enddef;

picture pct;
pct:=btex this is a \rlap{test} etex;

beginfig(0)
draw pct;
draw bbox pct withpen pencircle scaled 2;
draw auxbbox pct withcolor red;
interim bboxmargin:=0; % temporary modification
draw auxbbox pct withcolor green;
endfig;

truecorners:=1;

beginfig(1)
draw pct;
draw bbox pct withpen pencircle scaled 2;
draw auxbbox pct withcolor red;
interim bboxmargin:=0; % temporary modification
draw auxbbox pct withcolor green;
endfig;

end
--%<-- test.mp

In your example MetaPost behaves as it should; but as François Piétard 
noticed, 'gtpart.cls' lies about dimensions.

Regards,
Laurent Méhats

> 2013/3/13 Stefan Witzel <s.witzel at uni-muenster.de>:
>> Hi,
>>
>> ok, this is good to know, though bbox is such a suggestive name. But
>> maybe I should explain my problem. Actually no bounding box is
>> supposed to be there in the end. I just noticed that my labels are all
>> over the place when using this new document class and tried to figure
>> out why. As you can see in the attached image (with bbox and the
>> actual bounding box) something goes wrong in determining the
>> dimensions of the typeset text. But when I compile the debugging tex
>> file (I added a vrule to see the left boundary) I get the rather
>> reasonable looking pdf file attached.
>> I also attached the metapost source. The document class is available
>> at http://www.msp.warwick.ac.uk/agt/macros/gtpart.cls. I am grateful
>> for suggestions about what might cause this problem.
>>
>> Best,
>> Stefan
>>
>> 2013/3/13 Hans Hagen <pragma at wxs.nl>:
>>> On 3/12/2013 10:41 PM, Stefan Witzel wrote:
>>>>
>>>> Hi,
>>>>
>>>> thanks Taco and Hans for the quick replies!
>>>>
>>>> 2013/3/12 Hans Hagen <pragma at wxs.nl>:
>>>>>
>>>>> The bbox depends on the ht/dp of characters and lines and often the
>>>>> character boundingbox is not tight (and when you use type one fonts and
>>>>> traditional tex characters this is even more true due to limitation s of
>>>>> the
>>>>> machinery).
>>>>
>>>>
>>>> In my case it's actually very strange: the text exceeds the bounding
>>>> box by an apparently fixed amount to the left. For example if I do
>>>>
>>>> draw(btex this is a test etex)
>>>> draw(bbox(btex this is a test etex))
>>>>
>>>> the "th" wil stick out of the box. But hopefully the debugging will
>>>> bring clarification (I'll try tomorrow).
>>>
>>>
>>> ah .. youre not usinmg the boundingbox at all, but bbox which adds a margin
>>> of 1 pt by default (bbmargin or so)
>>>
>>> just look at the attached:
>>>
>>> page 1: boundingbox currentpicture overlaid
>>> page 2: bbox currentpicture overlaid
>>> page 3: both overlaid
>>>
>>>
>>> -----------------------------------------------------------------
>>>                                            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
>>> -----------------------------------------------------------------
>>
>>
>>
>> --
>> Dr. Stefan Witzel
>> Mathematisches Institut der Universität Münster
>> Einsteinstraße 62
>> 48149 Münster
>> http://wwwmath.uni-muenster.de/u/stefan.witzel
>
>
>