[screen-devel] [bug #33756] Cursor positioning fails due to incorrect width assumptions

[Thomas Wolff]

URL:
  <http://savannah.gnu.org/bugs/?33756>

                 Summary: Cursor positioning fails due to incorrect width
assumptions
                 Project: GNU Screen
            Submitted by: towo
            Submitted on: Tue 12 Jul 2011 16:36:12 GMT
                Category: Program Logic
                Severity: 3 - Normal
                Priority: 5 - Normal
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.2
           Fixed Release: None
         Planned Release: None
           Work Required: None

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Details:

Apparently screen transforms absolute cursor positioning escape sequences
from the application into relative ones towards the host terminal.

This is fatal practice whenever screen's assumption of character width
does not reflect the actual width on the terminal.

This is particularly the case if screen is invoked with a locale environment
not matching the terminal character encoding, e.g. with LC_ALL=C in a
UTF-8 terminal, see screenshot menu1.png where screen fails miserably
to position the menu borders (which are properly placed by the application).
Note that this (arguably misconfigured) environment is not unlikely to
occur in a network after remote login.

The problem occurs, however, also if locale setup is proper, due to the
many different versions of Unicode character width data. So around
double-width characters the problem may still occur and spoil the
display layout, see screenshot menu2.png.

I don't think this transformation (probably to save a few bytes occasionally)
is a proper thing to do, it is not transparent handling of the application's
escape sequences in any case. Please change it.



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File Attachments:


-------------------------------------------------------
Date: Tue 12 Jul 2011 16:36:12 GMT  Name: menu1.png  Size: 26kB   By: towo

<http://savannah.gnu.org/bugs/download.php?file_id=23645>
-------------------------------------------------------
Date: Tue 12 Jul 2011 16:36:12 GMT  Name: menu2.png  Size: 25kB   By: towo

<http://savannah.gnu.org/bugs/download.php?file_id=23646>

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