1curs_bkgd(3X) curs_bkgd(3X)
2
6 bkgdset, wbkgdset, bkgd, wbkgd, getbkgd - curses window background ma‐
7 nipulation routines
8
10 #include <curses.h>
11 void bkgdset(chtype ch);
13 void wbkgdset(WINDOW *win, chtype ch);
14 int bkgd(chtype ch);
16 int wbkgd(WINDOW *win, chtype ch);
17 chtype getbkgd(WINDOW *win);
19
21 bkgdset
22 The bkgdset and wbkgdset routines set the background for a window. A
23 window's background is a chtype consisting of any combination of at‐
24 tributes (i.e., rendition) and a character:
25 • The attribute part of the background is combined (OR'ed) with all
27 non-blank characters that are written into the window with waddch.
28 • Both the character and attribute parts of the background are com‐
30 bined with blank characters that are written into the window.
31 The background becomes a property of each character and moves with the
33 character through any scrolling and insert/delete line/character opera‐
34 tions.
35 To the extent possible on a particular terminal, the attribute part of
37 the background is displayed as the graphic rendition of the character
38 put on the screen.
39 bkgd
41 The bkgd and wbkgd functions set the background property of the current
42 or specified window and then apply this setting to every character po‐
43 sition in that window. According to X/Open Curses, it should do this:
44 • The rendition of every character on the screen is changed to the
46 new background rendition.
47 • Wherever the former background character appears, it is changed to
49 the new background character.
50 Neither X/Open Curses nor the SVr4 manual pages give details about the
52 way the rendition of characters on the screen is updated when bkgd or
53 wbkgd is used to change the background character.
54 This implementation, like SVr4 curses, does not store the background
56 and window attribute contributions to each cell separately. It updates
57 the rendition by comparing the character, non-color attributes and col‐
58 ors contained in the background. For each cell in the window, whether
59 or not it is blank:
60 • The library first compares the character, and if it matches the
62 current character part of the background, it replaces that with the
63 new background character.
64 When bkgdset is used to set the background character, that does not
66 update each cell in the window. A subsequent call to bkgd will
67 only modify the character in cells which match the current back‐
68 ground character.
69 • The library then checks if the cell uses color, i.e., its color
71 pair value is nonzero. If not, it simply replaces the attributes
72 and color pair in the cell with those from the new background char‐
73 acter.
74 • If the cell uses color, and that matches the color in the current
76 background, the library removes attributes which may have come from
77 the current background and adds attributes from the new background.
78 It finishes by setting the cell to use the color from the new back‐
79 ground.
80 • If the cell uses color, and that does not match the color in the
82 current background, the library updates only the non-color at‐
83 tributes, first removing those which may have come from the current
84 background, and then adding attributes from the new background.
85 If the background's character value is zero (0), a space is assumed.
87 If the terminal does not support color, or if color has not been
89 started with start_color, the new background character's color attri‐
90 bute will be ignored.
91 getbkgd
93 The getbkgd function returns the given window's current background
94 character/attribute pair.
95
97 These functions are described in the XSI Curses standard, Issue 4. It
98 specifies that bkgd and wbkgd return ERR on failure, but gives no fail‐
99 ure conditions.
100 The routines bkgd and wbkgd return the integer OK, unless the library
102 has not been initialized.
103 In contrast, the SVr4.0 manual says bkgd and wbkgd may return OK "or a
105 non-negative integer if immedok is set", which refers to the return
106 value from wrefresh (used to implement the immediate repainting). The
107 SVr4 curses wrefresh returns the number of characters written to the
108 screen during the refresh. This implementation does not do that.
109
111 Note that bkgdset and bkgd may be macros.
112 X/Open Curses mentions that the character part of the background must
114 be a single-byte value. This implementation, like SVr4, checks to en‐
115 sure that, and will reuse the old background character if the check
116 fails.
117
119 These functions are described in the XSI Curses standard, Issue 4
120 (X/Open Curses).
121
123 curses(3X), curs_addch(3X), curs_attr(3X), curs_outopts(3X)
124 curs_bkgd(3X)