Curses and resizing windows

Discussion in 'Python' started by Nick !, Feb 28, 2007.

  1. Nick !

    Nick ! Guest

    > Chris Share <usenet at caesium.me.uk> wrote:
    > > I've been writing an application using curses, and have been trying to
    > > handle resizing the terminal, if running in xterm or similar. Increasing
    > > the window size is working perfectly, however shrinking it is not
    > > working at all. No matter how much I shrink the window, the size
    > > returned by getmaxyx() does not change. However as soon as I increase it
    > > again, it works fine.

    >
    > > I've tracked the problem down to the fact I have created a window
    > > derived from stdscr. A small script showing the effect is at the end of
    > > this post.

    >
    > odd (thanks for the example - I don't know if this is a problem in
    > ncurses or in the python interface to it, but will check/see).
    >
    > > Can anyone suggest how to solve this problem, that doesn't involve not
    > > making a derwin of stdscr?

    >
    > > I've been googling for hours, but found nothing to help.

    >
    > > Python version is 2.3.4 on debian testing.

    >
    > probably should report it as a bug (so it's not overlooked).
    >
    > --
    > Thomas E. Dickey
    > http://invisible-island.net
    > ftp://invisible-island.net


    http://web.cs.mun.ca/~rod/ncurses/ncurses.html#xterm says "The ncurses
    library does not catch [the SIGWINCH aka resizing] signal, because it
    cannot in general know how you want the screen re-painted". First, is
    this really true? When I make my xterms smaller they clip what is
    displayed--is that a function of curses or the xterm?
    Second, if true, it explains /what/ is going on--stdscr, only--, but
    isn't really satisfactory; it doesn't solve the original poster's bug.

    #!/usr/bin/env python
    """
    curses_resize.py -> run the program without hooking SIGWINCH
    curses_resize.py 1 -> run the program with hooking SIGWINCH
    """


    import sys, curses, signal, time

    def sigwinch_handler(n, frame):
    curses.endwin()
    curses.initscr()

    def main(stdscr):
    """just repeatedly redraw a long string to reveal the window boundaries"""
    while 1:
    stdscr.insstr(0,0,"abcd"*40)
    time.sleep(1)

    if __name__=='__main__':
    if len(sys.argv)==2 and sys.argv[1]=="1":
    signal.signal(signal.SIGWINCH, sigwinch_handler)
    curses.wrapper(main)

    If you run this without sigwinch then the line never gets resized, but
    if you do then it works fine. What we can glean from this is that
    stdscr only reads off it's size upon initialization. This behaviour
    may seem a bit strange, but 1) it's legacy and 2) avoids breaking the
    semantics of windows (which don't change size on their own).

    The "curses.initscr()" part is kind of unhappy though. It modifies the
    stdscr variable without us explicitly assigning anything (but I can't
    think of any other way to do it, beyond making stdscr a global, and
    that feels worse) and will break if initscr() ever returns a new
    Window structure instead of just updating and returning the old one.
    Does anyone have any tips for how to structure this so that the screen
    can actually be assigned to?

    In conclusion, it's not a bug, it's a feature. Joy! The workaround is
    to write a sigwinch_handler that at least does `endwin(); initscr()`.

    Sorry for reviving an old thread, but it doesn't seem the issue was
    ever resolved (the thread doesn't go anywhere and there's no warning
    about this in the docs that I noticed).

    (please CC: me if anyone cares, I'm not on the list)

    -Nick Guenther
     
    Nick !, Feb 28, 2007
    #1
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  2. Nick ! <> wrote:

    > http://web.cs.mun.ca/~rod/ncurses/ncurses.html#xterm says "The ncurses
    > library does not catch [the SIGWINCH aka resizing] signal, because it
    > cannot in general know how you want the screen re-painted". First, is
    > this really true? When I make my xterms smaller they clip what is


    no - given that particular url is a file dating from 1995, it's something
    that I overlooked in making corrections here:

    http://invisible-island.net/ncurses/ncurses-intro.html

    But also note where I link it from:

    http://invisible-island.net/ncurses/ncurses.faq.html#additional_reading

    > displayed--is that a function of curses or the xterm?


    both - xterm sends the signal, and curses receives it.

    > Second, if true, it explains /what/ is going on--stdscr, only--, but
    > isn't really satisfactory; it doesn't solve the original poster's bug.


    > #!/usr/bin/env python
    > """
    > curses_resize.py -> run the program without hooking SIGWINCH
    > curses_resize.py 1 -> run the program with hooking SIGWINCH
    > """



    > import sys, curses, signal, time


    > def sigwinch_handler(n, frame):
    > curses.endwin()
    > curses.initscr()


    Actually I'd expect to see curses.refresh() here - but that may be a quirk
    of the python code.

    In general, ncurses passes a KEY_RESIZE via the getch() call that the
    application (such as python) should process. If it's not reading from
    getch(), ncurses' repainting/resizing won't happen.

    Also, if you add your own signal handler, ncurses' SIGWINCH catcher won't
    work. (I'd recommend chaining the signal handlers, but don't know if
    python supports that ;-).

    > def main(stdscr):
    > """just repeatedly redraw a long string to reveal the window boundaries"""
    > while 1:
    > stdscr.insstr(0,0,"abcd"*40)
    > time.sleep(1)


    > if __name__=='__main__':
    > if len(sys.argv)==2 and sys.argv[1]=="1":
    > signal.signal(signal.SIGWINCH, sigwinch_handler)
    > curses.wrapper(main)


    --
    Thomas E. Dickey
    http://invisible-island.net
    ftp://invisible-island.net
     
    Thomas Dickey, Feb 28, 2007
    #2
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