% notcurses_channels(3)
% nick black <nickblack@linux.com>
% v3.0.0

# NAME

notcurses_channels - operations on notcurses channels

# SYNOPSIS

**#include <notcurses/notcurses.h>**

```c
#define NCCHANNEL_INITIALIZER(r, g, b) \
  (((uint32_t)r << 16u) + ((uint32_t)g << 8u) + (b) + NC_BGDEFAULT_MASK)

#define NCCHANNELS_INITIALIZER(fr, fg, fb, br, bg, bb) \
  ((NCCHANNEL_INITIALIZER(fr, fg, fb) << 32ull) + \
   (NCCHANNEL_INITIALIZER(br, bg, bb)))
```

**uint32_t ncchannel_r(uint32_t ***channel***);**

**uint32_t ncchannel_g(uint32_t ***channel***);**

**uint32_t ncchannel_b(uint32_t ***channel***);**

**uint32_t ncchannel_rgb8(uint32_t ***channel***, uint32_t* restrict ***r***, uint32_t* restrict ***g***, uint32_t* restrict ***b***);**

**int ncchannel_set_rgb8(uint32_t* ***channel***, unsigned ***r***, unsigned ***g***, unsigned ***b***);**

**int ncchannel_set(uint32_t* ***channel***, uint32_t ***rgb***);**

**uint32_t ncchannel_alpha(uint32_t ***channel***);**

**int ncchannel_set_alpha(uint32_t* ***channel***, unsigned ***alpha***);**

**bool ncchannel_default_p(uint32_t ***channel***);**

**uint32_t ncchannel_set_default(uint32_t* ***channel***);**

**uint32_t ncchannels_fg_rgb(uint64_t ***channels***);**

**uint32_t ncchannels_bg_rgb(uint64_t ***channels***);**

**int ncchannels_set_fg_rgb(uint64_t* ***channels***, uint32_t ***rgb***);**

**int ncchannels_set_bg_rgb(uint64_t* ***channels***, uint32_t ***rgb***);**

**unsigned ncchannels_fg_alpha(uint64_t ***channels***);**

**unsigned ncchannels_bg_alpha(uint64_t ***channels***);**

**int ncchannels_set_fg_alpha(uint64_t* ***channels***, int ***alpha***);**

**int ncchannels_set_bg_alpha(uint64_t* ***channels***, int ***alpha***);**

**uint32_t ncchannels_fg_rgb8(uint64_t ***channels***, unsigned* ***r***, unsigned* ***g***, unsigned* ***b***);**

**uint32_t ncchannels_bg_rgb8(uint64_t ***channels***, unsigned* ***r***, unsigned* ***g***, unsigned* ***b***);**

**int ncchannels_set_fg_rgb8(uint64_t* ***channels***, unsigned ***r***, unsigned ***g***, unsigned ***b***);**

**int ncchannels_set_bg_rgb8(uint64_t* ***channels***, unsigned ***r***, unsigned ***g***, unsigned ***b***);**

**bool ncchannels_fg_default_p(uint64_t ***channels***);**

**bool ncchannels_bg_default_p(uint64_t ***channels***);**

**uint64_t ncchannels_set_fg_default(uint64_t* ***channels***);**

**uint64_t ncchannels_set_bg_default(uint64_t* ***channels***);**

**uint64_t ncchannels_reverse(uint64_t ***channels***);**

**unsigned ncchannel_palindex(uint32_t ***channel***);**

**bool ncchannel_palindex_p(uint32_t ***channel***);**

**int ncchannel_set_palindex(uint32_t* ***channel***, int ***idx***);**

**unsigned ncchannels_fg_palindex(uint64_t ***channels***);**

**unsigned ncchannels_bg_palindex(uint64_t ***channels***);**

**int ncchannels_set_fg_palindex(uint64_t* ***channels***, int ***idx***);**

**int ncchannels_set_bg_palindex(uint64_t* ***channels***, int ***idx***);**

**uint64_t ncchannels_combine(uint32_t ***fchan***, uint32_t ***bchan***);**

# DESCRIPTION

**ncchannel_palindex** extracts the palette index from a channel. The channel
must be palette-indexed, or the return value is meaningless. Verify palette
indexing with **ncchannel_palindex_p**. A channel can be set to palette
indexed mode (and have the index set) with **ncchannel_set_palindex**. The
index must be less than **NCPALETTESIZE**.

**ncchannels_combine** creates a new channel pair using ***fchan*** as the
foreground channel and ***bchan*** as the background channel.

# RETURN VALUES

Functions returning `int` return -1 on failure, or 0 on success. Failure is
always due to invalid inputs. Functions returning `bool` are predicates, and
return the requested value. Functions returning `unsigned` forms return the
input, modified as requested.

**ncchannels_reverse** inverts the color components of the two channels,
while holding all other elements constant. It's the Notcurses approximation
to reverse video.

# SEE ALSO

**notcurses(3)**,
**notcurses_cell(3)**,
**notcurses_plane(3)**,
**notcurses_output(3)**