1curs_bkgd(3X)                                                    curs_bkgd(3X)
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NAME

6       bkgdset,  wbkgdset,  bkgd,  wbkgd,  getbkgd  - curses window background
7       manipulation routines
8

SYNOPSIS

10       #include <curses.h>
11
12       void bkgdset(chtype ch);
13       void wbkgdset(WINDOW *win, chtype ch);
14       int bkgd(chtype ch);
15       int wbkgd(WINDOW *win, chtype ch);
16       chtype getbkgd(WINDOW *win);
17

DESCRIPTION

19   bkgdset
20       The bkgdset and wbkgdset routines  manipulate  the  background  of  the
21       named window.  The window background is a chtype consisting of any com‐
22       bination  of  attributes  (i.e.,  rendition)  and  a  character.    The
23       attribute part of the background is combined (OR'ed) with all non-blank
24       characters that are written into the  window  with  waddch.   Both  the
25       character  and  attribute parts of the background are combined with the
26       blank characters.  The background becomes a property of  the  character
27       and  moves  with  the character through any scrolling and insert/delete
28       line/character operations.
29
30       To the extent possible on a particular terminal, the attribute part  of
31       the  background  is displayed as the graphic rendition of the character
32       put on the screen.
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34   bkgd
35       The bkgd and wbkgd functions set the background property of the current
36       or  specified  window  and  then  apply this setting to every character
37       position in that window.  According to  X/Open  Curses,  it  should  do
38       this:
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40       ·   The  rendition  of  every character on the screen is changed to the
41           new background rendition.
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43       ·   Wherever the former background character appears, it is changed  to
44           the new background character.
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46       Neither  X/Open Curses nor the SVr4 manual pages give details about the
47       way the rendition of characters on the screen is updated when  bkgd  or
48       wbkgd is used to change the background character.
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50       This  implementation,  like  SVr4 curses, does not store the background
51       and window attribute contributions to each cell separately.  It updates
52       the rendition by comparing the character, non-color attributes and col‐
53       ors contained in the background.  For each cell in the window,  whether
54       or not it is blank:
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56       ·   The  library  first  compares  the character, and if it matches the
57           current character part of the background, it replaces that with the
58           new background character.
59
60       ·   The  library  then  checks  if the cell uses color, i.e., its color
61           pair value is nonzero.  If not, it simply replaces  the  attributes
62           and color pair in the cell with those from the new background char‐
63           acter.
64
65       ·   If the cell uses color, and that matches the color in  the  current
66           background, the library removes attributes which may have come from
67           the current background and adds attributes from the new background.
68           It finishes by setting the cell to use the color from the new back‐
69           ground.
70
71       ·   If the cell uses color, and that does not match the  color  in  the
72           current   background,   the  library  updates  only  the  non-color
73           attributes, first removing those which may have come from the  cur‐
74           rent  background,  and  then  adding  attributes from the new back‐
75           ground.
76
77       If the background's character value is zero, a space is assumed.
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79       If the terminal does not support  color,  or  if  color  has  not  been
80       started   with   start_color,  the  new  background  character's  color
81       attribute will be ignored.
82
83   getbkgd
84       The getbkgd function returns  the  given  window's  current  background
85       character/attribute pair.
86

RETURN VALUE

88       These  functions are described in the XSI Curses standard, Issue 4.  It
89       specifies that bkgd and wbkgd return ERR on failure, but gives no fail‐
90       ure conditions.
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92       The  routines  bkgd and wbkgd return the integer OK, unless the library
93       has not been initialized.
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95       In contrast, the SVr4.0 manual says bkgd and wbkgd may return OK "or  a
96       non-negative  integer  if  immedok  is set", which refers to the return
97       value from wrefresh (used to implement the immediate repainting).   The
98       SVr4  curses  wrefresh  returns the number of characters written to the
99       screen during the refresh.  This implementation does not do that.
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NOTES

102       Note that bkgdset and bkgd may be macros.
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104       X/Open Curses mentions that the character part of the  background  must
105       be  a  single-byte  value.   This  implementation, like SVr4, checks to
106       ensure that, and will reuse the old background character if  the  check
107       fails.
108

PORTABILITY

110       These  functions  are  described  in  the  XSI Curses standard, Issue 4
111       (X/Open Curses).
112

SEE ALSO

114       curses(3X), curs_addch(3X), curs_attr(3X), curs_outopts(3X)
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118                                                                 curs_bkgd(3X)
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