[luatex] line break reassigns font id with expansion

[Hans Hagen]

On 5/5/2013 2:15 PM, Philipp Gesang wrote:
> Hi all,
>
> with expansion enabled, line breaking assigns new font ids to
> glyph nodes. Example for luatex-plain:
>
> ·································································
> %\font\somefont=file:Iwona-Regular.otf
> \font\somefont=file:Iwona-Regular.otf:expansion=default;
> \somefont
> \pdfadjustspacing=2
> \catcode`\%=11
>
> \directlua{
>    local glyph_t    = node.id"glyph"
>    local hlist_t    = node.id"hlist"
>    local vlist_t    = node.id"vlist"
>    local sub_box_t  = node.id"sub_box"
>
>    local show_font_id
>    show_font_id = function (hd, when, nested)
>      for n in node.traverse(hd) do
>        local n_id = n.id
>        if n_id == glyph_t then
>          local n_font = n.font
>          local tfmdata = font.getfont(n_font)
>          print(string.format(
>                "(%s (rec %s) (byte %d) (chr %s) (font %s) (tfmdata %s))",
>                when,
>                nested,
>                n.char,
>                unicode.utf8.char(n.char),
>                n_font,
>                tfmdata))
>        elseif n_id == hlist_t or n_id == vlist_t or n_id == sub_box_t then
>          show_font_id(n.list, when, true)
>        end
>      end
>      return hd
>    end
>    callback.register(
>      "pre_linebreak_filter",
>      function (hd) return show_font_id(hd, "pre_line") end)
>    callback.register(
>      "post_linebreak_filter",
>      function (hd) return show_font_id(hd, "post_line") end)
>    callback.register(
>      "pre_output_filter",
>      function (hd) return show_font_id(hd, "pre_out") end)
> }
>
> \hsize 1cm
>
> foo bar
>
> \bye
> ·································································
>
> On my machine (version beta-0.76.0-2013040516), all glyphs have
> font 51 initially. During line breaking, those glyphs that are
> subject to expansion get reassigned font 53 or 54. I’m not sure
> whether this is caused by the font loader or the engine itself.
> Anyways, the font loader doesn’t create entries for font ids 53
> and 54 in fonts.hashes.identifiers.
>
> My question is thus: is there a way to get the original font id
> of an expanded glyph after line breaking, or at least to get the
> corresponding tfmdata?

As all my luatex mailing list mails get filtered through its own box 
(simply because most concerns latex issues) I never see such mails till 
I explicitly walk through that list. Anyhow, the answer to this is:

It's just the way it works, and we will not extend that interface.
In fact, I've done experiments with this already years ago and already 
cooked up a more efficient and clean method which will get implemented 
after this tex live freeze. It also gives a better separation between 
front and backend. I actually patched the engine while testing but 
Hartmut will do the final cleanup so we have to be patient. There is no 
need to waste time on intermediate hacking.

The current implementation is taken from pdftex and is also a research 
instrument and therefore inhits on-the-fly fontbuilding (as needed for 
bitmap fonts).

Hans


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