notcurses/doc/man/man3/notcurses_cell.3.md

% notcurses_cell(3)
% nick black <nickblack@linux.com>
% v2.0.2

# NAME

notcurses_cell - operations on notcurses cells

# SYNOPSIS

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

```c
// See DESCRIPTION below for information on EGC encoding
typedef struct cell {
  uint32_t gcluster;          // 4B → 4B
  uint8_t gcluster_backstop;  // 1B → 5B (8 bits of zero)
  uint8_t reserved;           // 1B → 6B (8 reserved bits, ought be zero)
  uint16_t stylemask;         // 2B → 8B (16 bits of NCSTYLE_* attributes)
  uint64_t channels;
} cell;

#define CELL_TRIVIAL_INITIALIZER \
 { .gcluster = '\0', .stylemask = 0, .channels = 0, }
#define CELL_SIMPLE_INITIALIZER(c) \
 { .gcluster = (c), .stylemask = 0, .channels = 0, }
#define CELL_INITIALIZER(c, s, chan) \
 { .gcluster = (c), .stylemask = (s), .channels = (chan), }

#define CELL_WIDEASIAN_MASK     0x8000000080000000ull
#define CELL_BGDEFAULT_MASK     0x0000000040000000ull
#define CELL_FGDEFAULT_MASK     (CELL_BGDEFAULT_MASK << 32u)
#define CELL_BG_RGB_MASK        0x0000000000ffffffull
#define CELL_FG_RGB_MASK        (CELL_BG_MASK << 32u)
#define CELL_BG_PALETTE         0x0000000008000000ull
#define CELL_FG_PALETTE         (CELL_BG_PALETTE << 32u)
#define CHANNEL_ALPHA_MASK      0x30000000ull
#define CELL_ALPHA_HIGHCONTRAST 0x30000000ull
#define CELL_ALPHA_TRANSPARENT  0x2.0.2000ull
#define CELL_ALPHA_BLEND        0x10000000ull
#define CELL_ALPHA_OPAQUE       0x00000000ull
```

**void cell_init(cell* c);**

**int cell_load(struct ncplane* n, cell* c, const char* gcluster);**

**int cell_prime(struct ncplane* n, cell* c, const char* gcluster,
                 uint32_t stylemask, uint64_t channels);**

**int cell_duplicate(struct ncplane* n, cell* targ, const cell* c);**

**void cell_release(struct ncplane* n, cell* c);**

**void cell_styles_set(cell* c, unsigned stylebits);**

**unsigned cell_styles(const cell* c);**

**void cell_styles_on(cell* c, unsigned stylebits);**

**void cell_styles_off(cell* c, unsigned stylebits);**

**void cell_set_fg_default(cell* c);**

**void cell_set_bg_default(cell* c);**

**int cell_set_fg_alpha(cell* c, unsigned alpha);**

**int cell_set_bg_alpha(cell* c, unsigned alpha);**

**bool cell_double_wide_p(const cell* c);**

**const char* cell_extended_gcluster(const struct ncplane* n, const cell* c);**

**char* cell_strdup(const struct ncplane* n, const cell* c);**

**int cell_load_simple(struct ncplane* n, cell* c, char ch);**

**char* cell_extract(const struct ncplane* n, const cell* c, uint16_t* stylemask, uint64_t* channels);**

**uint32_t cell_bchannel(const cell* cl);**

**uint32_t cell_fchannel(const cell* cl);**

**uint64_t cell_set_bchannel(cell* cl, uint32_t channel);**

**uint64_t cell_set_fchannel(cell* cl, uint32_t channel);**

**uint32_t cell_fg_rgb(const cell* cl);**

**uint32_t cell_bg_rgb(const cell* cl);**

**unsigned cell_fg_alpha(const cell* cl);**

**unsigned cell_bg_alpha(const cell* cl);**

**unsigned cell_fg_rgb8(const cell* cl, unsigned* r, unsigned* g, unsigned* b);**

**unsigned cell_bg_rgb8(const cell* cl, unsigned* r, unsigned* g, unsigned* b);**

**int cell_set_fg_rgb8(cell* cl, int r, int g, int b);**

**int cell_set_bg_rgb8(cell* cl, int r, int g, int b);**

**void cell_set_fg_rgb8_clipped(cell* cl, int r, int g, int b);**

**void cell_set_bg_rgb8_clipped(cell* cl, int r, int g, int b);**

**int cell_set_fg_rgb(cell* c, uint32_t channel);**

**int cell_set_bg_rgb(cell* c, uint32_t channel);**

**bool cell_fg_default_p(const cell* cl);**

**bool cell_bg_default_p(const cell* cl);**

**int ncstrwidth(const char* text)**;

# DESCRIPTION

Cells make up the framebuffer associated with each plane, with one cell per
addressable coordinate. You should not usually need to interact directly
with cells.

Each **cell** contains exactly one extended grapheme cluster. If the EGC
is encoded in UTF-8 with four or fewer bytes (all Unicode codepoints as of
Unicode 13 can be encoded in no more than four UTF-8 bytes), it is encoded
directly into the **cell**'s **gcluster** field, and no additional storage
is necessary. Otherwise, the EGC is stored as a nul-terminated UTF-8 string in
some backing egcpool. Egcpools are associated with **ncplane**s, so **cell**s
must be considered associated with **ncplane**s. Indeed, **ncplane_erase()**
destroys the backing storage for all a plane's cells, invalidating them. This
association is formed at the time of **cell_load()**, **cell_prime()**, or
**cell_duplicate()**. All of these functions first call **cell_release()**, as
does **cell_load_simple()**. When done using a **cell** entirely, call
**cell_release()**. **ncplane_destroy()** will free up the memory used by the
**cell**, but the backing egcpool has a maximum size of 16MiB, and failure to
release **cell**s can eventually block new output.

**cell_extended_gcluster** provides a nul-terminated handle to the EGC. This
ought be considered invalidated by changes to the **cell** or **egcpool**.
The handle is **not** heap-allocated; do **not** attempt to **free(3)** it.
A heap-allocated copy can be acquired with **cell_strdup**.

# RETURN VALUES

**cell_load()** and similar functions return the number of bytes loaded from the
EGC, or -1 on failure. They can fail due to either an invalid UTF-8 input, or the
backing egcpool reaching its maximum size.

**cell_set_fg_rgb8()** and similar functions will return -1 if provided invalid
inputs, and 0 otherwise.

# SEE ALSO

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