.\"*************************************************************************** .\" Copyright 2018-2024,2025 Thomas E. Dickey * .\" Copyright 1998-2015,2017 Free Software Foundation, Inc. * .\" * .\" Permission is hereby granted, free of charge, to any person obtaining a * .\" copy of this software and associated documentation files (the * .\" "Software"), to deal in the Software without restriction, including * .\" without limitation the rights to use, copy, modify, merge, publish, * .\" distribute, distribute with modifications, sublicense, and/or sell * .\" copies of the Software, and to permit persons to whom the Software is * .\" furnished to do so, subject to the following conditions: * .\" * .\" The above copyright notice and this permission notice shall be included * .\" in all copies or substantial portions of the Software. * .\" * .\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS * .\" OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF * .\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. * .\" IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, * .\" DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR * .\" OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR * .\" THE USE OR OTHER DEALINGS IN THE SOFTWARE. * .\" * .\" Except as contained in this notice, the name(s) of the above copyright * .\" holders shall not be used in advertising or otherwise to promote the * .\" sale, use or other dealings in this Software without prior written * .\" authorization. * .\"*************************************************************************** .\" .\" $Id: curs_bkgd.3x,v 1.74 2025/01/19 00:49:39 tom Exp $ .TH curs_bkgd 3X 2025-01-18 "ncurses 6.5" "Library calls" .ie \n(.g \{\ .ds `` \(lq .ds '' \(rq .\} .el \{\ .ie t .ds `` `` .el .ds `` "" .ie t .ds '' '' .el .ds '' "" .\} . .de bP .ie n .IP \(bu 4 .el .IP \(bu 2 .. .SH NAME \fB\%bkgdset\fP, \fB\%wbkgdset\fP, \fB\%bkgd\fP, \fB\%wbkgd\fP, \fB\%getbkgd\fP \- manipulate background of a \fIcurses\fR window of characters .SH SYNOPSIS .nf \fB#include .PP \fBint bkgd(chtype \fIch\fP); \fBint wbkgd(WINDOW *\fIwin\fP, chtype \fIch\fP); .PP \fBvoid bkgdset(chtype \fIch\fP); \fBvoid wbkgdset(WINDOW *\fIwin\fP, chtype \fIch\fP); .PP \fBchtype getbkgd(WINDOW *\fIwin\fP); .fi .SH DESCRIPTION Every .I curses window has a .I "background character" property: in the library's non-wide configuration, it is a .I curses character .RI \%( chtype ) that combines a set of attributes (and, if colors are enabled, a color pair identifier) with a character code. When erasing (parts of) a window, .I curses replaces the erased cells with the background character. .PP .I curses also uses the background character when writing characters to a populated window. .bP The attribute part of the background character combines with all non-blank character cells in the window, as populated by the \fB\%waddch\fP(3X) and \fB\%winsch\fP(3X) families of functions (and those that call them). .bP Both the character code and attributes of the background character combine with blank character cells in the window. .PP The background character's set of attributes becomes a property of the character cell and move with it through any scrolling and insert/delete line/character operations. To the extent possible on the terminal type, .I curses displays the attributes of the background character as the graphic rendition of a character cell on the display. .SS "bkgd, wbkgd" .B \%bkgd and .B \%wbkgd set the background property of .B \%stdscr or the specified window and then apply this setting to every character cell in that window. .bP The rendition of every character in the window changes to the new background rendition. .bP Wherever the former background character appears, it changes to the new background character. .PP .I \%ncurses updates the rendition of each character cell by comparing the character, non-color attributes, and color pair selection. The library applies the following procedure to each cell in the window, whether or not it is blank. .bP .I \%ncurses first compares the cell's character to the previously specified background character; if they match, .I \%ncurses writes the new background character to the cell. .bP .I \%ncurses then checks whether the cell uses color; that is, its color pair value is nonzero. If not, it simply replaces the attributes and color pair in the cell with those from the new background character. .bP If the cell uses color, and its background color matches that of the current window background, .I \%ncurses removes attributes that may have come from the current background and adds those from the new background. It finishes by setting the cell's background to use the new window background color. .bP If the cell uses color, and its background color does not match that of the current window background, .I \%ncurses updates only the non-color attributes, first removing those that may have come from the current background, and then adding attributes from the new background. .PP If the new background's character is non-spacing (for example, if it is a control character), .I \%ncurses retains the existing background character, except for one special case: .I \%ncurses treats a background character code of zero (0) as a space. .PP If the terminal does not support color, or if color has not been initialized with \fB\%start_color\fP(3X), .I \%ncurses ignores the new background character's color pair selection. .SS "bkgdset, wbkgdset" .B \%bkgdset and .B \%wbkgdset manipulate the background of the applicable window, without updating the character cells as .B \%bkgd and .B \%wbkgd do; only future writes reflect the updated background. .SS getbkgd .B \%getbkgd returns the given window's background character, attributes, and color pair as a .IR \%chtype "." .SH RETURN VALUE .B \%bkgdset and .B \%wbkgdset do not return a value. .PP Functions returning an .I int return .B ERR upon failure and .B OK upon success. In .IR \%ncurses "," failure occurs if .bP the .I curses screen has not been initialized, or .bP .I win is .IR NULL "." .PP .BR \%getbkgd 's return value is as described above. .SH NOTES Unusually, there is no .B \%wgetbkgd function; .B \%getbkgd behaves as one would expect .B \%wgetbkgd to, accepting a .I \%WINDOW pointer argument. .PP .B \%bkgd and .B \%bkgdset may be implemented as macros. .PP X/Open Curses mentions that the character part of the background must be a single-byte value. .IR \%ncurses "," like SVr4 .IR curses "," checks to ensure that it is, and retains the existing background character if the check fails. .SH PORTABILITY X/Open Curses Issue\ 4 describes these functions. It indicates that .IR bkgd "," .IR wbkgd "," and .I getbkgd return .I ERR on failure (in the case of the last, this value is cast to .IR \%chtype ), but specifies no error conditions for them. .PP SVr4 documentation .\" SVID 4, vol. 3, p. 482 says that .I \%bkgd and .I \%wbkgd return .I OK \*(``or a non-negative integer if .I \%immedok() \" Courier roman in source is set\*('', referring to the return value from .IR \%wrefresh "," which in SVr4 returns a count of characters written to the window if its .I \%immedok property is set; .\" ...though its wrefresh() man page says nothing about immedok()... in .IR \%ncurses "," it does not. .PP Neither X/Open Curses nor the SVr4 manual pages detail how the rendition of characters in the window updates when .I \%bkgd or .I \%wbkgd changes the background character. .IR \%ncurses "," like SVr4 .IR curses "," does not (in its non-wide configuration) store the background and window attribute contributions to each character cell separately. .SH HISTORY SVr3.1 (1987) introduced these functions. .SH SEE ALSO \fB\%curs_bkgrnd\fP(3X) describes the corresponding functions in the wide configuration of .IR \%ncurses "." .PP \fB\%curses\fP(3X), \fB\%curs_addch\fP(3X), \fB\%curs_attr\fP(3X)