[Konsole-devel] Bug#41744: konsole Shows some Japanese FULLWIDTH chars as HALFWIDTH

[Waldo Bastian]

On Friday 26 April 2002 10:52 pm, asataku at osk3.3web.ne.jp wrote:
> Package: konsole
> Version: 1.2 Preview (using KDE 3.0.5 (CVS HEAD >= 20020412))
> Severity: normal
> Installed from:    compiled sources
> Compiler:          gcc version 2.95.3 20010315 (release)
> OS:                Linux (i686) release 2.4.18-0vl3
> OS/Compiler notes:
>
> Some of Japanese FULLWIDTH symbol chars shown as HALFWIDTH.
>
> I put example EUC-JP codec file on
> http://www.kde.gr.jp/~asaki/konsole-symbols.txt
>
> These chars are shown FULLWIDTH in kterm(Kanji-terminal).
> http://www.kde.gr.jp/~asaki/kterm.png
>
>
> And konsole shows HALFWIDTH.
> http://www.kde.gr.jp/~asaki/konsole.png
> But Japanese terminal application treats them as FULLWIDTH.
> So screen is broken.

Than you very much for your feedback. Anaysis of the problem follows.

It seems that the screen drawing methods used in konsole are inadequate for 
solving this. Our functions in konsole_wterm determine for each character 
whether it should be treated as half width or full width based on the 
unicode-value. However, this assumes that the font that is being used 
provides glyphs with corresponding half- or full width. If the width of the 
glyphs does not correspond with what we assume based on the results from the 
konsole_wterm functions then screen drawing will become a mess.

The characters from http://www.kde.gr.jp/~asaki/konsole-symbols.txt that are 
shown fullwidth in kterm, clearly only have halfwidth glyphs available in the 
selected font. I do not know how we could possibly obtain fullwidth glyphs.

A partial solution could be to change the screen-drawing from segment based to 
character based. That way we can ensure, even when a glyph has a size other 
than what we assume that it will have, that the next characters will be drawn 
on the correct position. This would also make it possible to use 
non-fixed-width fonts. Such a change would result in a loss of performance so 
we might want to detect the cases where such an approach would be beneficial 
(e.g. when using either non-fixed-width fonts or double-width characters)

I do not know whether konsole_wterm reports the mentioned characters as 
full-width or half-width. But that should be easy to find out.

Cheers,
Waldo
-- 
bastian at kde.org  |   SuSE Labs KDE Developer  |  bastian at suse.com