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vt100utils

A single-header C library for encoding, decoding, and doing useful things with ANSI graphics escape sequences.

This library is specifically targeted at graphics sequences because they are particularly useful for building terminal user interfaces, such as in my library tuibox.

By separating plain (visible) text from its formatting, previously-challenging tasks such as text wrapping, formatting changes, and truncation become relatively straightforward.

Demos

Content-aware text wrapping (overflow.c):

Text truncation with animation (hover.c):

Per-word interactivity (words.c):

Features

Decoder capable of parsing any arbitrary string and producing a list of text nodes
Encoder capable of producing a terminal-compatible string from a list of text nodes
Supports 8-color and 256-color palettes, as well as truecolor (16 million color) foreground and background
Supports special formatting such as bold, underline, italic, and blinking text
Fault-tolerant: Ignores unrecognized escape sequences (instead of aborting)

Basic Usage

A sample program is as follows:

#include "vt100utils.h"

int
main(void)
{
  struct vt100_node_t *head = vt100_decode("\x1b[32mHello world!\x1b[45;4mGoodbye."),
                      *tmp = head;

  while (tmp != NULL) {
    printf(
      "Text: %s\n  Foreground: %i\n  Background: %i\n  Mode: %i\n\n",
      tmp->str,
      tmp->fg.value,
      tmp->bg.value,
      tmp->mode
    );

    tmp = tmp->next;
  }

  vt100_free(head);

  return 0;
}

This code produces the following output:

Text:
  Foreground: 7
  Background: 0
  Mode: 0

Text: Hello world!
  Foreground: 2
  Background: 0
  Mode: 0

Text: Goodbye.
  Foreground: 2
  Background: 5
  Mode: 8

The `vt100_node_t` and `vt100_color_t` Structs

These two structs encode information about a given text node, and are defined as follows:

struct vt100_color_t {
  enum {
    palette_8,
    palette_8_bright,
    palette_256,
    truecolor
  } type;
  uint32_t value;
};

struct vt100_node_t {
  char    *str;
  int      len;
  struct vt100_color_t fg;
  struct vt100_color_t bg;
  uint8_t  mode;
  struct vt100_node_t *next;
};

When vt100_decode is called, a linked list consisting of vt100_node_t structs is built. Each of these contain the following information:

Their plain text content as a null-terminated string (as well as the length of the content)
The text's foreground and background colors as vt100_color_t structs:
- The type: 8-color palette, 8-color bright palette, 256-color palette, or truecolor
- The value: For palette-based color schemes, the index within the palette (e.g. 0 for color #30 in the 8-color standard palette). For truecolor, an RGB-encoded uint32_t.
The text's special formatting (its "mode"): Each bit represents one formatting type (e.g. bold, underline, italic, etc.).
- To check for any single formatting type, AND this value with 1 << (i - 1) where i is the ANSI code for enabling it (e.g. 1 for bold, 3 for italic, etc.)
The pointer to the next text node in the chain

As is standard for ANSI escape sequences, nodes inherit the formatting of prior nodes unless overwritten.

Along with this, calling vt100_encode does not produce an identical string to the one passed to vt100_decode. Instead, it should produce a string that looks identical when rendered in a terminal.