[texhax] LuaLaTeX: increase font expansion in narrow columns
zappathustra at free.fr
Wed Oct 19 19:18:59 CEST 2011
Le 19/10/2011 14:23, Arno Trautmann a écrit :
> Paul Isambert wrote:
>> Alleged shepherd Philip TAYLOR wrote:
>>> "A man who would letter-space lower-case text
>>> would probably steal sheep" : F W Goudy.
>> Stealing sheep is better than starving to death. See attached file.
> Do you also have an example (font expansion) vs. (font expansion +
> stolen sheep)? I find it hard to judge what the effect of sheep is in
> that example.
Use the following when you want to steal sheep:
local g = node.new(node.id"glue")
local spec = node.new(node.id"glue_spec")
spec.width = tex.sp"0pt"
spec.stretch = tex.sp".5pt"
g.spec = spec
local p = node.new(node.id"penalty")
local function stealsheep (h)
for n in node.traverse_id(node.id"glyph", h) do
if n.prev and n.prev.id == node.id"glyph" then
local g = node.copy(g)
node.insert_before(h, n, g)
node.insert_before(h, g, node.copy(p))
The .5pt stretch (and null shrink) is totally arbitrary. Also, the code
isn't very good (it doesn't handle discretionary nodes, nor glyphs
separated by a font kern), but it's just to give an idea. It is easily
amended if you wish to do that.
> Sticking to font expansion, I wondered if the following could work in
> • as changing the expansion is not possible, change the font in narrow
> lines, i.e. load the font twice with different expansions.
> • in post_linebreak_filter, collect all subsequent narrow lines
> • pack them back into one hlist, change the font to the one with
> larger expansion, break this hlist into a paragraph with the same
> number of lines as before.
Which means create a paragraph with narrow lines and no \parfillskip
(obviously). Plus the same number of lines. Plus you have to remove
existing hyphenation. But that's doable :)
> • put that list of hlists back into the vertikal list.
> I don't have to mention that I am not able to even try to translate
> this into code, do I? …
You can do that, Arno. You said what needed to be done, translating it
into code is the easiest part.
> Also, related to this question: Is there any technical documentation
> on how pdfTeX (or, if it differs in that case, LuaTeX) breaks lines
> into paragraphs using font expansion and character protrusion? I mean
> something like the corresponding chapter in the TeXbook – I'd like to
> understand at which point and how font expansion is taken into account
> in the line breaking.
If you ever find that, I'll be glad to know.
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