Re: Issue with wbkgrnd and wide chars on ncurses 6.2

[Thomas Dickey]

On Sat, Jan 30, 2021 at 08:21:26PM +0100, Anton Vidovic wrote:
> Hello Thomas,
> 
> I contacted you last April [0] about a bug I encountered while working on
> a Common Lisp binding for ncurses.

thanks (I didn't forget this - it was one of two regressions that I'd
like to repair before ncurses 6.3)
 
> As far as I could, I tracked down the source of the bug to the following
> line 209 in ncurses/base/lib_bkgd.c

offhand, I'd have thought this was the issue (given the comments),

        /* SVr4 limits background character to printable 7-bits */
        if (!Charable(new_bkgd)) {
            new_char = old_char;
        }
> 
> for (y = 0; y <= win->_maxy; y++) {
>     int x;
>     for (x = 0; x <= win->_maxx; x++) {
>       NCURSES_CH_T *cp = &(win->_line[y].text[x]);
>       int tmp_pair = GetPair(*cp);
>       attr_t tmp_attr = AttrOf(*cp);
> 
>       if (CharEq(*cp, old_bkgd)) {
> >>>>      SetChar2(*cp, CharOf(new_char));    <<<<<<<
>       }
> 
> In ncurses 6.1, instead of the call to SetChar2, we directly set the
> character at y,x to the character set by the call to wbkgrndset.
> 
> win->_line[y].text[x] = win->_nc_bkgd;
> 
> In addition to the minimal example in Lisp [2] I provided last year,
> this would be equivalent minimal example in C:
> 
> #define _XOPEN_SOURCE_EXTENDED
> #include <locale.h>
> #include <ncurses.h>
> 
> int main()
> {
>     cchar_t cch;
>     const wchar_t wch[2] = {L'\u2591', L'\0'};
> 
>     setlocale(LC_ALL, "");
>     setcchar(&cch,
>              wch,
>              0,
>              0,
>              NULL);
> 
>     initscr();
>     bkgrnd(&cch);
>     refresh();
>     getch();
>     endwin();
>     printf("%lc\n", wch[0]);
>     return 0;
> }
> 
> This allows setting single-byte chars like 'A' as a background char,
> but if any wide char like L'\u2591' is passed, it is simply ignored.
> 
> Last year I did not have success replicating the bug in C, but in the
> meantime I have upgraded my machine, and now with a fresh install of
> Ubuntu 20.04 with a default install of ncurses 6.2.20200212, the C
> example replicates the behavior I encountered with Lisp.
> 
> I hope you will find an opportunity to address this issue.

I guess this (barring build-problems...) is next on my to-do list

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

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