alloc_pair, find_pair, free_pair - new curses color-pair
functions
#include <ncurses/curses.h>
int alloc_pair(int fg, int bg);
int find_pair(int fg, int bg);
int free_pair(int pair);
These functions are an extension to the curses 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.
The number of colors may be related to the number of possible
color pairs for a given terminal, or it may not:
- Beyond that lies in the realm of programs using the foreground and
background colors for “ASCII art” (or some other non-textual
application).
- Also beyond those few dozen pairs, the required size for a table to
represent the combinations grows rapidly with an increasing number of
colors.
- These functions allow a developer to let the screen library manage color
pairs.
The alloc_pair function accepts parameters for foreground and background
color, and checks if that color combination is already associated with a color
pair.
- If the combination already exists, alloc_pair returns the existing
pair.
- If the combination does not exist, alloc_pair allocates a new color
pair and returns that.
- If the table fills up, alloc_pair discards the least-recently
allocated entry using free_pair and allocates a new color
pair.
All of the color pairs are allocated from a table of possible
color pairs. The size of the table is determined by the terminfo
pairs capability. The table is shared with init_pair; in fact
alloc_pair calls init_pair after updating the ncurses
library's fast index to the colors versus color pairs.
The find_pair 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.
Marks the given color pair as unused, i.e., like color pair 0.
The alloc_pair function returns a color pair number in the range 1
through COLOR_PAIRS-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.
The find_pair function returns a color pair number if the
given color combination has been associated with a color pair, or -1 if
not.
Likewise, free_pair returns OK unless it encounters
an error updating the fast index or if no such color pair is in use.
These routines are specific to ncurses. They were not supported on Version 7,
BSD or System V implementations. It is recommended that any code depending on
them be conditioned using NCURSES_VERSION.