Re: Off-screen panels/windows

[Thomas Dickey]

On Sat, Aug 08, 2020 at 03:52:09PM -0400, Bill Gray wrote:
> Hello all,
> 
>    I've been working for some years on a fork of PDCurses.  As a
> result,  I often refer to ncurses to get a sense of what the
> behavior "ought" to be.  (When there's a bug or poor behavior,
> it's almost always on the PDCurses side.  I don't think I've
> encountered a reportable ncurses issue.  This is my first post
> to this list,  and it's still not because ncurses is wrong.)
> 
>    Recently,  I investigated some issues in the PDCurses panels
> library.  I wrote a small demo to put three panels on-screen :
> 
> https://github.com/Bill-Gray/PDCursesMod/blob/master/demos/test_pan.c
> 
>    Run this in a terminal,  grab the lower right corner of the terminal
> and shrink it so that the windows stick off-screen,  and it all works
> if the program is compiled with ncurses.  To my knowledge,  this is
> the only way in ncurses or PDCurses to get a window to be partly or
> completely off-screen.  You can't call mvwin() to do it,  but if a
> user resizes the terminal,  ncurses handles the off-screen panel
> correctly.  (Are there other ways to get partially or fully off-screen

hmm - ncurses' resizeterm doesn't pay attention to panels (just windows).

I'd expect the windows associated with the panels to be resized/limited
to be on-screen (if not, a bug...)

> windows/panels in ncurses?)
> 
>    My fork of PDCurses crashed when required to handle off-screen
> panels/windows,  but that was easy to fix.
> 
>    I then tried commenting out lines 294-296 at
> 
> https://github.com/Bill-Gray/PDCursesMod/blob/126a8df8f33e64439a12e7ecbe0685804d0ef00c/pdcurses/window.c#L294
> 
>    ...i.e.,  "go ahead and allow mvwin() to put windows off-screen."
> Thus far,  I've seen no problems with this;  I can move panels
> partly or completely off-screen,  much as one can with windows in
> a traditional GUI.  Which seems as if it could be useful.
> 
>    Is there a reason ncurses requires windows/panels to be on-screen
> (with the exception of resized terminals)?  Out of caution,  I'm

iirc, it's for compatibility with SVr4 curses
though that X/Open Curses in general has that, because of mvwin:

https://pubs.opengroup.org/onlinepubs/7908799/xcurses/mvwin.html

(that is, you shouldn't be able to create a window in a place that you
can't move the window to).

-- 
Thomas E. Dickey <dickey@invisible-island.net>
https://invisible-island.net
ftp://ftp.invisible-island.net

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