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List:       vim-multibyte
Subject:    Re: Double width character is displayed as broken.
From:       Bram Moolenaar <Bram () moolenaar ! net>
Date:       2006-10-07 13:32:45
Message-ID: 200610071332.k97DWj78051996 () moolenaar ! net
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Yukihiro Nakadaira wrote:

> When using GUI and 'encoding' is utf-8, double width character is
> sometimes displayed as broken.  I wrote a patch.  Please check the
> following.
> 
> For example, please look this screenshot.
> 
>   http://yukihiro.nakadaira.googlepages.com/screenshot.png
> 
> There are single width character 'a' and multi-byte character 'A'.  And
> 'a' is highlighted.
> 
> After double width character 'B' is inserted, the second half of 'B' is
> same value of 'A' (ScreenLinesUC is not cleared.  It keeps old value).
> 
>           offset |0|1|2|3|4|5|
>                  |a| A |
>                     |
>                     | ScreenLinesUC is not cleared.
>                     v
>           offset |0|1|2|3|4|5|
>    insert 'B' -> | B |a| A |
>                     ^ ScreenLinesUC == 'A'
> 
> Then, insert NL.  Vim clear the line from 'a' to EOL.
> 
>                     +- ScreenLineUC == 'A'
>                     v
>           offset |0|1|2|3|4|5|
>                  | B |a| A |
>                      |-----------> to be cleared
> 
> If 'a' is highlighted, Vim redraw its previous character ('B').  But Vim
> doesn't care about double width character.  Then, wrong offset is used.
> 
>   First, redraw the previous character with wrong offset.
> 
>                   +----- the first half of 'B'
>                   | +--- ScreenLineUC[off - 1] == 'A' was drawn
>                   | | +- off
>                   v v v
>           offset |0|1|2|3|4|5|
>                  |B| A | A |
>                      |-----------> to be cleared
> 
>   Second, clear the rest of line.
> 
>                   +----- the first half of 'B'
>                   | +--- the first half of 'A'
>                   | | +- the second half of 'A' was cleared
>                   v v v
>           offset |0|1|2|3|4|5|
>                  |B|A|
> 
>   Result, double width character 'B' is displayed as broken.
> 
>          line 1: |0|1|2|3|4|5|
>          line 2: |B|A|
>          line 3: |a| A |

Thanks for the clear explanation and the patch!  I could reproduce the
problem, I'll include the patch.

-- 
Shift happens.
                -- Doppler

 /// Bram Moolenaar -- Bram@Moolenaar.net -- http://www.Moolenaar.net   \\\
///        sponsor Vim, vote for features -- http://www.Vim.org/sponsor/ \\\
\\\        download, build and distribute -- http://www.A-A-P.org        ///
 \\\            help me help AIDS victims -- http://ICCF-Holland.org    ///
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