[luatex] CJK vertical typesetting

[Dohyun Kim]

Hi,

CJK vertical typesetting can be implemented thanks to the RTT mode
provided by luatex engine; at current development stage, however,
some round-about seems to be necessary.

Please compare the drawing of "*TT" in fontdir.pdf under manual directory
and the image at http://fontforge.sourceforge.net/charview.html#Vertical .
In the latter image, it seems that the height is the right side length
of baseline; depth is the left side length; and width is the "vertical
advance."

Perhaps the width of a glyph vertically typesetted should be the value of
vertical advance, that is "vwidth" as is returned by fontloader library.
But in current RTT mode we only have to reassign height and depth
instead of width.

So I have tried to do vertical typesetting by following procedure.
1.  assign height of vertical glyph = 0
2.  assign depth of vertical glyph = vwidth of this glyph
3.  in "pre_linebreak_filter," xoffset the glyph by the value of
"ascender" of font.

Then it works well now. But if luatex uses the width, instead of
height and depth, for glyph advancement in RTT mode,
the implementation could have been much simpler.
Is this possible? or should I stick to my round-about way?
or is there another more legitimate way?

Regards,
-- 
Dohyun Kim
College of Law, Dongguk University
Seoul, Republic of Korea