.\"*************************************************************************** .\" Copyright 2018-2022,2023 Thomas E. Dickey * .\" Copyright 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. * .\"*************************************************************************** .\" .\" Author: Thomas E. Dickey .\" .\" $Id: new_pair.3x,v 1.44 2023/12/16 20:32:22 tom Exp $ .TH new_pair 3NCURSES 2023-12-16 "ncurses 6.4" "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\%alloc_pair\fP, \fB\%find_pair\fP, \fB\%free_pair\fP \- dynamically allocate \fIcurses\fR color pairs .SH SYNOPSIS .nf \fB#include .PP \fBint alloc_pair(int \fIfg\fP, int \fIbg\fP); \fBint find_pair(int \fIfg\fP, int \fIbg\fP); \fBint free_pair(int \fIpair\fP); .fi .SH DESCRIPTION These functions are an extension to the \fIcurses\fP library. They permit an application to dynamically allocate a color pair using the foreground/background colors rather than assign a fixed color pair number, and return an unused pair to the pool. .PP The number of colors may be related to the number of possible color pairs for a given terminal, or it may not: .bP While almost all terminals allow setting the color \fIattributes\fP independently, it is unlikely that your terminal allows you to modify the attributes of a given character cell without rewriting it. That is, the foreground and background colors are applied as a pair. .bP Color pairs are the \fIcurses\fP library's way of managing a color palette on a terminal. If the library does not keep track of the \fIcombinations\fP of colors which are displayed, it will be inefficient. .IP \(bu 4 For simple terminal emulators with only a few dozen color combinations, it is convenient to use the maximum number of combinations as the limit on color pairs: .PP .RS 8 .EX \fBCOLORS\fI * \fBCOLORS\fR .EE .RE .IP \(bu 4 Terminals which support \fIdefault colors\fP distinct from \*(``ANSI colors\*('' add to the possible combinations, producing this total: .PP .RS 8 .EX \fI( \fBCOLORS\fI + 1 ) * ( \fBCOLORS\fI + 1 )\fR .EE .RE .bP An application might use up to a few dozen color pairs to implement a predefined color scheme. .IP Beyond that lies in the realm of programs using the foreground and background colors for \*(``ASCII art\*('' (or some other non-textual application). .IP Also beyond those few dozen pairs, the required size for a table to represent the combinations grows rapidly with an increasing number of colors. .IP These functions allow a developer to let the screen library manage color pairs. .SS alloc_pair The \fBalloc_pair\fP function accepts parameters for foreground and background color, and checks if that color combination is already associated with a color pair. .bP If the combination already exists, \fBalloc_pair\fP returns the existing pair. .bP If the combination does not exist, \fBalloc_pair\fP allocates a new color pair and returns that. .bP If the table fills up, \fBalloc_pair\fP discards the least-recently allocated entry using \fBfree_pair\fP and allocates a new color pair. .PP All of the color pairs are allocated from a table of possible color pairs. The size of the table is determined by the terminfo \fBpairs\fP capability. The table is shared with \fBinit_pair\fP; in fact \fBalloc_pair\fP calls \fBinit_pair\fP after updating the \fI\%ncurses\fP library's fast index to the colors versus color pairs. .SS find_pair The \fBfind_pair\fP function accepts parameters for foreground and background color, and checks if that color combination is already associated with a color pair, returning the pair number if it has been allocated. Otherwise it returns \-1. .SS free_pair Marks the given color pair as unused, i.e., like color pair 0. .SH RETURN VALUE The \fBalloc_pair\fP function returns a color pair number in the range 1 through \fBCOLOR_PAIRS\fP\-1, unless it encounters an error updating its fast index to the color pair values, preventing it from allocating a color pair. In that case, it returns \-1. .PP The \fBfind_pair\fP function returns a color pair number if the given color combination has been associated with a color pair, or \-1 if not. .PP Likewise, \fBfree_pair\fP returns \fBOK\fP unless it encounters an error updating the fast index or if no such color pair is in use. .SH PORTABILITY These routines are specific to \fI\%ncurses\fP. They were not supported on Version 7, BSD or System V implementations. It is recommended that any code depending on them be conditioned using \fB\%NCURSES_VERSION\fP. .SH AUTHORS Thomas Dickey .SH SEE ALSO \fB\%color\fP(3NCURSES)