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Re: ncurses 5.7 set_field_back problem

From: Thomas Dickey
Subject: Re: ncurses 5.7 set_field_back problem
Date: Sat, 03 Dec 2011 15:55:30 -0500
User-agent: Mutt/1.5.18 (2008-05-17)

On Fri, Dec 02, 2011 at 08:43:54PM -0500, Thomas Dickey wrote:
> The log works as expected for xterm.  At the moment (I'll have more time
> tomorrow), I have only the "pterm" (putty on Linux) program to check PuTTY. 
> That doesn't support blink, but uses colors to represent it.  With that, I see
> a difference in the way it is rendering the fields before text is written on
> them: the first field gets colored and the second does not.  This is before
> the text is written on the fields.

hmm - you said you were using Reflections (Friday's bad for thinking -
looks like I just recalled "Windows" client).

Today I tested with putty running on Windows 7 (putty 0.61).
Oddly, it doesn't have the same issue with blinking text as the pterm
0.60 on my Linux machine.  PuTTY's changelog isn't much help.

Still... it's the same symptom.

> \E[34X
> The "\E[34X" is an erase control, which is probably clearing the
> blinking attribute away from the field.  In the terminal description
> for putty, that is this chunk:
>       ech=\E[%p1%dX,

I have a manual for Reflections 7, and it says that it does support ECH
(as I would expect).

well... if ECH clears only the character, but not attributes, that could
be a bug that I'd have to fix.

However -

The VT420 reference manual says (of ECH - erase character)

        This control function erases one or more characters, from the cursor
        position to the right. ECH clears character attributes from erased
        character positions. ECH works inside or outside the scrolling margins.

"character attributes" (chapter 7) are:
        bold, underline, blinking, negative image, invisible.

Based on that, I think that xterm and ncurses are correct, and that there's
a bug in the older PuTTY version.  It's a puzzling bug since it seems to
have the effect of XOR'ing the attribute, so that reapplying the attribute
unsets it.  I've made a note to add some test screens to vttest (to be able
to compare results).

Suppressing the "ech" capability from your terminal description would
seem the best way to go - something that you could do.  Which $TERM
value is that?

Thomas E. Dickey <address@hidden>

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