[Dev-luatex] Modifying the LuaTeX Engine

Yue Wang yuleopen at gmail.com
Tue Dec 30 18:57:58 CET 2008


Hi:

WOW! This is very impressive! Thanks for your work.

 So I think we can add vertical CJK typesetting feature to LuaTeX/MKIV
next year?

[Wolfgang is busy writing the wishlist for cjk typesetting, so i think
he will be very interested in experimenting your results]

Yue Wang

On Tue, Dec 30, 2008 at 4:08 PM, Arthur Reutenauer
<arthur.reutenauer at normalesup.org> wrote:
>> Can you show me an example of vertical typesetting in LuaTeX?
>
>  Try the attached file.  It demonstrates vertical typesetting with LuaTeX in
> three steps; unfortunately it only works in DVI mode for the moment
> because the PDF output is completely buggy, I discussed with Taco about
> that.
>
>  1. At first, you simply need to switch to vertical directions, using the
> primitives inherited from Omega.  Here I used LTL as the general direction: the
> first letter indicates the first edge of the page is at the left (lines of text
> move globally from left to right); 'T' means the second edge of the page is at
> the top (inside a single line, text moves from the top downwards).  The last
> letter defines the notion of "top" for individual letters, I chose left, more
> or less randomly.  It has some influence, as we will see later, but not as much
> as the first two letters.
>
>  Then you can set English text vertically, with the columns running from left
> to right.  It's akward to use OpenType fonts in DVI mode, so I simply used
> Computer Modern Typewriter, stacking the letters on top of each other.  Of
> course it's weird to set English text vertically without rotating the letters,
> but it is possible.  There is a problem, though, because the text looks
> completely clumsy: the reason is the font's metrics are not designed for
> vertical typesetting, so you need to change them.  The way metrics work in
> Omega's directional model is that width runs along the direction of the line,
> here top-to-bottom; hence a glyph's width, in that example, is actually the sum
> of its height and its depth in the original font designed for horizontal
> typesetting. Its height and depth, in turn, need to be chosen so that their sum
> is equal to the horizontal width, and I think it's a good choice to make them
> equal to each other, so that each glyph is centered on the vertical base line.
>
>  2. On the second page I demonstrate a first way to do that, with Lua code:
> you can use the define_font callback to redefine width, height and depth for
> each glyph in the font, and LuaTeX will use these new metrics.
>
>  Note that the vertical width should, actually, be a little bit more than
> horizontal height + horizontal depth, because these dimensions are not meant to
> blend well with stacks of letters, unlike the horizontal width: the former are
> really more like the dimensions of a bounding box, whereas the latter is the
> distance by which you should advance the line of text in order for the text not
> to look to crowded.  Thus, I cheated a bit, by stretching the vertical width by
> 30% (chosen, again, at random by trial and error).
>
>  But that's still not enough: as you can see, letters with descender, like 'g'
> in the first line, sticks into the next letter.  That's because it has a
> horizontal depth, and its origin is thus too low with respect to its enclosing
> box: we need to raise those letters by their horizontal depth.
>
>  3.  We could do this by editing the font and modify every glyph so that it
> sits on the baseline, but we can do better by using virtual fonts.  In LuaTeX,
> there are two ways to use virtual fonts: you can use a .vf file, or you can
> define it with Lua commands in the font data.  Unfortunately, the latter
> doesn't work in DVI mode because your Lua code is lost once the DVI file is
> produced, and your DVI reader / driver doesn't know how to create the font, so
> we have to stick to the traditional method and produce a .vf file.  I wrote a
> small script to that effect which you will find in the attached zip, but the
> .vf and .tfm files are also attached anyway.  Now the text looks quite nice, in
> my opinion.  It's still hard to read, but that's of course because English is
> not supposed to be typeset that way.
>
>  The (figurative) bottom line of all this is that you need to typeset vertical
> text with fonts that have vertical metrics.  Once the problems with PDF mode
> are fixed, I can try and do that with Chinese or Japanese fonts; I expect it
> would be quite straightforward.
>
>        Arthur
>


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