python derwin() behavior with pdcurses library

[michael-lazar]

I'm starting an issue to investigate the observed broken behavior of python's curses.derwin() with pdcurses. There appears to be an issue with the two argument form of derwin (See https://github.com/michael-lazar/rtv/pull/31 for details from @peterpans01). This is not really an RTV issue, but I'm curious none the less.

[michael-lazar]

From cpython/Modules/_cursesmodule.c, line 1075

static PyObject *
PyCursesWindow_DerWin(PyCursesWindowObject *self, PyObject *args)
{
    WINDOW *win;
    int nlines, ncols, begin_y, begin_x;

    nlines = 0;
    ncols  = 0;
    switch (PyTuple_Size(args)) {
    case 2:
        if (!PyArg_ParseTuple(args,"ii;begin_y,begin_x",&begin_y,&begin_x))
            return NULL;
        break;
    case 4:
        if (!PyArg_ParseTuple(args, "iiii;nlines,ncols,begin_y,begin_x",
                              &nlines,&ncols,&begin_y,&begin_x))
            return NULL;
        break;
    default:
        PyErr_SetString(PyExc_TypeError, "derwin requires 2 or 4 arguments");
        return NULL;
    }

    win = derwin(self->win,nlines,ncols,begin_y,begin_x);

    if (win == NULL) {
        PyErr_SetString(PyCursesError, catchall_NULL);
        return NULL;
    }

    return (PyObject *)PyCursesWindow_New(win, NULL);
}

So the two argument form in Python sends derwin(0, 0, begin_y, begin_x) to the curses library.

From ncurses-5.9/ncurses/base, line 186

derwin(WINDOW *orig, int num_lines, int num_columns, int begy, int begx)
{
    WINDOW *win;
    int i;
    int flags = _SUBWIN;
#if NCURSES_SP_FUNCS
    SCREEN *sp = _nc_screen_of(orig);
#endif

    T((T_CALLED("derwin(%p,%d,%d,%d,%d)"), (void *) orig, num_lines, num_columns,
       begy, begx));

    /*
     * make sure window fits inside the original one
     */
    if (begy < 0 || begx < 0 || orig == 0 || num_lines < 0 || num_columns < 0)
        returnWin(0);
    if (begy + num_lines > orig->_maxy + 1
        || begx + num_columns > orig->_maxx + 1)
        returnWin(0);

    if (num_lines == 0)
        num_lines = orig->_maxy + 1 - begy;

    if (num_columns == 0)
        num_columns = orig->_maxx + 1 - begx;

    if (orig->_flags & _ISPAD)
        flags |= _ISPAD;

    win = NCURSES_SP_NAME(_nc_makenew) (NCURSES_SP_ARGx num_lines, num_columns,
                                        orig->_begy + begy,
                                        orig->_begx + begx, flags);
    if (win == 0)
        returnWin(0);

    win->_pary = begy;
    win->_parx = begx;
    WINDOW_ATTRS(win) = WINDOW_ATTRS(orig);
    win->_nc_bkgd = orig->_nc_bkgd;

    for (i = 0; i < num_lines; i++)
        win->_line[i].text = &orig->_line[begy++].text[begx];

    win->_parent = orig;

    returnWin(win);
}

and from PDCurses-3.4/pdcurses/window.c

line 341

WINDOW *derwin(WINDOW *orig, int nlines, int ncols, int begy, int begx)
{
    return subwin(orig, nlines, ncols, begy + orig->_begy, begx + orig->_begx);
}

line 294

WINDOW *subwin(WINDOW *orig, int nlines, int ncols, int begy, int begx)
{
    WINDOW *win;
    int i;
    int j = begy - orig->_begy;
    int k = begx - orig->_begx;

    PDC_LOG(("subwin() - called: lines %d cols %d begy %d begx %d\n",
             nlines, ncols, begy, begx));

    /* make sure window fits inside the original one */

    if (!orig || (begy < orig->_begy) || (begx < orig->_begx) ||
        (begy + nlines) > (orig->_begy + orig->_maxy) ||
        (begx + ncols) > (orig->_begx + orig->_maxx))
        return (WINDOW *)NULL;

    if (!nlines)
        nlines = orig->_maxy - 1 - j;
    if (!ncols)
        ncols  = orig->_maxx - 1 - k;

    if ( !(win = PDC_makenew(nlines, ncols, begy, begx)) )
        return (WINDOW *)NULL;

[michael-lazar]

Dropped all attempts at maintaining windows compatability a long time ago.

[Brobin]

:D #linuxmasterrace