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Re: CDK & Terminal Resizing

From: Marc Smith
Subject: Re: CDK & Terminal Resizing
Date: Sat, 9 Apr 2011 21:30:02 -0400

On Sat, Apr 9, 2011 at 8:58 PM, Thomas Dickey <address@hidden> wrote:
> On Sat, 9 Apr 2011, Marc Smith wrote:
>> Thanks for the quick reply.
>> So, for now, I'm not too worried about making the widgets look right
>> if the user resizes (to something smaller). However, I would like to
>> make my program able to "recover" if the user shrinks the terminal to
>> something smaller than the original.
>> I'm new to ncurses and CDK, so maybe this is something simple I'm
>> missing. Lets say on my screen I have all my widgets up and then the
>> user makes the terminal say 1x1 and then expands it back to the
>> original size (or greater). I've tried calling refreshCDKScreen()
>> after the screen is back to the original size, but that doesn't seem
>> to fix the widgets. Any ideas?
> yes - same issues, more details.  CDK doesn't know about resizable screens.
>  It could be modified to re-layout its widgets to fit in a smaller screen,
> or to increase a widget.  (I haven't done it - usual reason - time).
>  ncurses resizes some of the "easy" cases, to be helpful,
> but that doesn't give a complete solution - the application (CDK) has to
> do work.
> Supposing that it were modified to be resizable, it would have to ensure
> that the data would be presented in roughly the same way (for example, the
> same current line in a selection list).  It would also have to have some way
> to tell it that some widgets have limits on their intended size (and what
> part has to be visible on a 1x1 screen).

I will look at the CDK source and your ideas for implementing resizing
in CDK and maybe give it a stab -- I will have some extra time on my
hands this summer after school.

I still don't understand why refreshCDKScreen() doesn't fix the
screen/widgets after a resize. Eg, screen with widgets is displayed
with size of 20x70, a user then resizes the terminal to say 2x2 and
then back to 20x70.

The screen is back at the original size but the widgets are messed up
-- even after a refreshCDKScreen().

I was thinking refreshCDKScreen() would walk though all of the widgets
and redraw the screen, character by character.

>> --Marc
>> On Fri, Apr 8, 2011 at 8:29 PM, Thomas Dickey <address@hidden> wrote:
>>> On Fri, 8 Apr 2011, Marc Smith wrote:
>>>> Hi,
>>>> I didn't see a separate list for "ncurses user questions", so I'm
>>>> assuming this list is for that as well. If not, I'd appreciate it if
>>>> anyone could redirect me to the right place.
>>>> So, I'm using CDK (5.0.20081105) (ncurses 5.7) to develop a text user
>>>> interface. Resizing terminals doesn't seem to play nice with the CDK
>>>> widgets -- the text on the screen is messed up after resizing the
>>>> terminal to something smaller than what was started with and then back
>>>> to the original size (or bigger).
>>> yes - it doesn't do that...
>>> I'd done this more/less for dialog.  It was much simpler than CDK would
>>> be.
>>>> I've experimented with other ncurses related things (mc, dialog, etc.)
>>>> and they seem to resize correctly. I understand I can catch the
>>>> SIGWINCH via KEY_RESIZE / getch() and I am able to do that, but I'm
>>>> not sure how I can make the widgets resize "nicely". I've tried using
>>>> refreshCDKScreen() and others, but I can't get it.
>>> There's more than one thing which would have to be done.
>>> When the keypad() function is enabled (which it is), then
>>> the ncurses getch/wgetch returns KEY_RESIZE when it has updated
>>> stdscr/curscr to respond to the SIGWINCH.
>>> At that point, in dialog, I provided for a jump back to the
>>> initialization
>>> region of a widget, so it would then fall into the getch-loop.
>>> CDK wraps calls to wgetch in getchCDKObject.  Some are buried down a
>>> level
>>> or two, making it impractical to "jump back" (other than a setjmp).
>>> I think, that to make SIGWINCH work here, CDK would have to be
>>> reorganized
>>> to use some sort of event-loop (keeping the wgetch's at that level), and
>>> to
>>> add a list of the widgets, which the event-loop function could adjust in
>>> one
>>> place.
>>> Alternatively (closer to how CDK is done now), it could have a method
>>> added
>>> to each widget to tell it to resize.
>>>> I'm sure this is something that could be modified in CDK for the
>>>> widgets to resize nicely, but how can I do this in my own program
>>>> without modifying CDK? Any ideas?
>>> You'd have to (in effect) write your own resize functions and register
>>> them
>>> as callbacks.  It's probably doable (since the WINDOW's are exposed in
>>> the
>>> widget structures), but rather tedious to implement for the whole
>>> library.
>>> --
>>> Thomas E. Dickey
>>> http://invisible-island.net
>>> ftp://invisible-island.net
> --
> Thomas E. Dickey
> http://invisible-island.net
> ftp://invisible-island.net

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