underline problem

[Kenichi Handa]

I recently installed some fix for incorrect underline
drawing, but I found another problem.

For instance, when you customize the default face to have
underline, visit the HELLO file, and move cursor on some
non-ASCII characters that is displayed by a font that has
different underline-position than the default face (in my
case, on Arabic characters), the underline is shown at the
different position even if Emacs has a code to draw
underline at the same position as the previous glyphs as
below.

          if (s->prev && s->prev->face->underline_p)
            {
              /* We use the same underline style as the previous one.  */
              thickness = s->prev->underline_thickness;
              position = s->prev->underline_position;
            }
          else

It seems that this problem is because that the redisplay
engine builds a glyph string only for the characters at the
cursor, thus the code mentioned above has no way to know the
underline style of previous glyphs.

For the moment, the only solution I can think of is to
decide the underline position (and thickness) for each frame
from the default font, and always use it for the frame.

Any better idea?

---
Kenichi Handa
address@hidden