[NTG-pdftex] character protrusion with the first letter in a paragraph

The Thanh Han hanthethanh at myrealbox.com
Wed Jan 19 12:47:57 CET 2005


On Tue, Jan 18, 2005 at 10:57:10PM +0100, Hartmut Henkel wrote:
> On Mon, 15 Nov 2004, Hans Hagen wrote:
> 
> > The Thanh Han wrote:
> > >
> > > I have been thinking of the question how to make char protrusion
> > > work with the first char of a paragraph. The simplest (and quite
> > > robust) solution can be as follows: when considering whether a
> > > marginal kern should be inserted, we skip certain kinds of
> > > `invisible' node (like adjust node, penalty node and the like). Now
> > > to make it work with the first char of a par, we also skip null
> > > boxes (box with zero dimen and empty contents) at the left margin.
> > > The question is whether such behaviour is ``correct'', and what
> > > surprises it can bring in certain situations.
> >
> > there are several solutions possible:
> >
> > <nothing><null box>text text text text
> >
> > here it looks safe to me to do as you suggest, it can of course be
> > made into an option, say \pdfprotrudeparstart=1 or so
> >
> > <something><null box>text text text text
> 
> these two cases i tried to handle in the experimental patch 257. At
> paragraph start the empty \hbox{} inserted by TeX is skipped, if
> \parindent=0pt. Else, inside the paragraph the discardable items at line
> start are skipped. Then the cp_skipable things are skipped, while diving
> in and out \hboxes, if any.
> 
> > is more tricky since one may use the box in order to prevent
> > protruding; on the other hand, if you ignore all null boxes, then it
> > maybe nice to have something
> >
> > \noprotrusion, which introduces a special node, which in itself may be
> > tricky, although pdftex introduces new nodes anyway
> 
> Also any empty or non-empty box with some height or depth does this, e.
> g. "\vphantom." Maybe that's enough?

definitively. How to *block* protrusion is trivial. How to make it work
is more tricky :)

> > I can also imagine something \pdfprotrudeleft (and right) that can be
> > inserted manually (or everypar'd; in that case it would be handy to
> > finally have \everyendpar available as well); imagine:
> >
> > \pdfprotrudeleft \hbox {somechar} some text
> >
> > \pdfprotrudeleft \hbox {\hbox {somechar}} some text
> 
> at least now it would find "somechar" inside the box if this is
> protrudable.

making char protrusion work with metarial inside boxes is already a bug
step and would solve a lot of problems.

> > how difficult is it to let pdftex in that case follow the list until
> > it finds a char (here 's'); this woudl permit things like
> >
> > \pdfprotrudeleft \hbox {x\hskip-2pt x} some text
> 
> To _hide_ the whole \hbox until "s" is found and active at the margin?
> 
> Or should one allow protrusion of "s" in things like \llap{foo}s?

I don't know what it can be good for. If there is a need to protrude
something that is not a character, using some virtual character may
solve the problem faster.

Thanh


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