Re: Confusion about NCURSES_PAIRS_T

[Thomas Dickey]

On Mon, Apr 15, 2019 at 02:57:56PM +0800, Chih-Hsuan Yen wrote:
> Hi NCurses experts,
> 
> Currently (v6_1_20190413) NCURSES_PAIRS_T is defined as `short`, and
> in function `pair_content()`, the first argument `pair` accepts
> 1~COLOR_PAIRS-1, which is 1~65535 in some terminal types (e.g.,
> xterm-256color, screen-256color). Does that mean NCURSES_PAIRS_T
> should be a type with a larger range?

no - that would make ncurses incompatible with X/Open Curses,
rather than being an extended implementation.

I introduced NCURSES_PAIRS_T in 2014:
https://invisible-island.net/ncurses/NEWS.html#t20140201

        + add/use symbol NCURSES_PAIRS_T like NCURSES_COLOR_T, to illustrate
          which "short" types are for color pairs and which are color values.

referring to this in curses.h:

/*
 * The standard type used for color values, and for color-pairs.  The latter
 * allows the curses library to enumerate the combinations of foreground and
 * background colors used by an application, and is normally the product of the
 * total foreground and background colors.
 *
 * X/Open uses "short" for both of these types, ultimately because they are
 * numbers from the SVr4 terminal database, which uses 16-bit signed values.
 */
#undef  NCURSES_COLOR_T
#define NCURSES_COLOR_T short

#undef  NCURSES_PAIRS_T
#define NCURSES_PAIRS_T short

X/Open Curses uses "short" in function-prototypes (but does not document
details of data structures).  It's not possible to change the function
prototypes to use "int" without being incompatible.

I added NCURSES_COLOR_T (and NCURSES_SIZE_T) in 2000 while considering
this problem:

https://invisible-island.net/ncurses/NEWS.html#t20000429

        + add symbol NCURSES_SIZE_T to use rather than explicit 'short' for
          internal window and pad sizes.  Note that since this is visible in
          the WINDOW struct, it would be an ABI change to make this an 'int'
          (prompted by a question by Bastian Trompetter

That is actually "configurable", but (currently) not worth the
trouble to extend it:

/*
 * The internal type used for window dimensions.
 */
#undef  NCURSES_SIZE_T
#define NCURSES_SIZE_T short

Sure: some newer/improved terminal descriptions cannot be represented
in a standard X/Open Curses implementation.  To do this, I used new
functions and an unused parameter in several functions to pass the
extended color values to the library.

I spent most of 2017 working on this, taking into account
binary compatibility:

https://invisible-island.net/ncurses/announce.html
https://invisible-island.net/ncurses/ncurses-slang.html

But what you're describing is a constraint within the python curses binding,
which I can only give advice about.

> Noticing this when debugging https://bugs.python.org/issue36630.

The basic problem there is that no one's gotten around to improving
the python curses binding to handle the newer terminal descriptions.

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

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