IO#erase_screen

static VALUE
console_erase_screen(VALUE io, VALUE val)
{
    rb_io_t *fptr;
    HANDLE h;
    rb_console_size_t ws;
    COORD *pos = &ws.dwCursorPosition;
    DWORD w;
    int mode = mode_in_range(val, 3, "screen erase");

    GetOpenFile(io, fptr);
    h = (HANDLE)rb_w32_get_osfhandle(GetWriteFD(fptr));
    if (!GetConsoleScreenBufferInfo(h, &ws)) {
        rb_syserr_fail(LAST_ERROR, 0);
    }
    w = winsize_col(&ws);
    switch (mode) {
      case 0:   /* erase after cursor */
        w = (w * (ws.srWindow.Bottom - pos->Y + 1) - pos->X);
        break;
      case 1:   /* erase before *and* cursor */
        w = (w * (pos->Y - ws.srWindow.Top) + pos->X + 1);
        pos->X = 0;
        pos->Y = ws.srWindow.Top;
        break;
      case 2:   /* erase entire screen */
        w = (w * winsize_row(&ws));
        pos->X = 0;
        pos->Y = ws.srWindow.Top;
        break;
      case 3:   /* erase entire screen */
        w = (w * ws.dwSize.Y);
        pos->X = 0;
        pos->Y = 0;
        break;
    }
    constat_clear(h, ws.wAttributes, w, *pos);
    return io;
}