From 74a684c269f97ab84ad7bac1d0966ab8dfa24338 Mon Sep 17 00:00:00 2001 From: funkpower Date: Thu, 22 Oct 2026 19:30:17 -0400 Subject: [PATCH] ansi: show ANSI art in a UTF-8 terminal, or as plain or shaded text Draws an .ans file into a grid the way an ANSI-BBS terminal would (cursor moves, the wrap at the SAUCE width, iCE colours) and writes it out as UTF-8: in colour, --plain, or --mono with coloured areas shaded by brightness. info prints the SAUCE record. One C99 file with no dependencies. --- .gitignore | 1 + LICENSE | 338 ++++++++++++++++++++++++++++++++++++++ Makefile | 18 ++ README.md | 38 +++++ ansi.1 | 69 ++++++++ ansi.c | 473 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 6 files changed, 937 insertions(+) create mode 100644 .gitignore create mode 100644 LICENSE create mode 100644 Makefile create mode 100644 README.md create mode 100644 ansi.1 create mode 100644 ansi.c diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..36c3479 --- /dev/null +++ b/.gitignore @@ -0,0 +1 @@ +ansi diff --git a/LICENSE b/LICENSE new file mode 100644 index 0000000..9efa6fb --- /dev/null +++ b/LICENSE @@ -0,0 +1,338 @@ + GNU GENERAL PUBLIC LICENSE + Version 2, June 1991 + + Copyright (C) 1989, 1991 Free Software Foundation, Inc., + + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + Preamble + + The licenses for most software are designed to take away your +freedom to share and change it. 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Of course, the commands you use may +be called something other than `show w' and `show c'; they could even be +mouse-clicks or menu items--whatever suits your program. + +You should also get your employer (if you work as a programmer) or your +school, if any, to sign a "copyright disclaimer" for the program, if +necessary. Here is a sample; alter the names: + + Yoyodyne, Inc., hereby disclaims all copyright interest in the program + `Gnomovision' (which makes passes at compilers) written by James Hacker. + + , 1 April 1989 + Moe Ghoul, President of Vice + +This General Public License does not permit incorporating your program into +proprietary programs. If your program is a subroutine library, you may +consider it more useful to permit linking proprietary applications with the +library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. diff --git a/Makefile b/Makefile new file mode 100644 index 0000000..f1a7224 --- /dev/null +++ b/Makefile @@ -0,0 +1,18 @@ +PREFIX ?= $(HOME) +BINDIR ?= $(PREFIX)/bin +MANDIR ?= $(PREFIX)/share/man/man1 +CFLAGS ?= -O2 +CFLAGS += -std=c99 -Wall -Wextra -pedantic + +ansi: ansi.c + $(CC) $(CFLAGS) $(LDFLAGS) -o $@ ansi.c + +install: ansi + install -d $(DESTDIR)$(BINDIR) $(DESTDIR)$(MANDIR) + install -m 755 ansi $(DESTDIR)$(BINDIR)/ansi + install -m 644 ansi.1 $(DESTDIR)$(MANDIR)/ansi.1 + +clean: + rm -f ansi + +.PHONY: install clean diff --git a/README.md b/README.md new file mode 100644 index 0000000..ca197af --- /dev/null +++ b/README.md @@ -0,0 +1,38 @@ +# ansi + +Show ANSI art in a modern terminal, or turn it into plain text. + +An `.ans` file is CP437 text with ANSI colour and cursor codes, laid out for an +80-column BBS terminal that wraps it. Converting it with `iconv` gets the +characters right but not the layout: a lot of art has no line breaks at all, and +much of it moves the cursor around. `ansi` draws the file into a grid the way a +BBS terminal would, then writes the grid out as UTF-8 lines. + +```console +$ ansi piece.ans | less -R # in colour +$ ansi --mono piece.ans > piece.txt # no colour, coloured areas as shading +$ ansi --plain piece.ans # the characters only +$ ansi info piece.ans # title, artist, group, date and size +$ curl -s https://16colo.rs/pack/dd26/raw/dd-cola.ans | ansi +``` + +`--mono` is for places that show no colour, like newsgroups and mail. Each +coloured area is redrawn by how bright its colour looks, so art built from +coloured spaces keeps its shape instead of going blank. + +It follows the SAUCE record for the width, shows blinking backgrounds bright +(iCE colour), and reads standard input when given no file or `-`. + +## Install + +One C99 file, no dependencies. + +```console +$ make +$ make install # into ~/bin and ~/share/man/man1 +$ make install PREFIX=/usr/local +``` + +## Licence + +GPL-2.0. See `LICENSE`. diff --git a/ansi.1 b/ansi.1 new file mode 100644 index 0000000..f9fe40d --- /dev/null +++ b/ansi.1 @@ -0,0 +1,69 @@ +.TH ANSI 1 "October 2026" "ansi 1.0.0" "User Commands" +.SH NAME +ansi \- show ANSI art in a UTF-8 terminal, or turn it into plain text +.SH SYNOPSIS +.B ansi +[\fB\-p\fR | \fB\-m\fR] [\fB\-w\fR \fIwidth\fR] [\fIfile\fR ...] +.br +.B ansi info +\fIfile\fR ... +.SH DESCRIPTION +ANSI art, the art of the BBS scene, is CP437 text with ANSI escape codes for +colour and cursor movement, laid out for a terminal of a fixed width, usually +80 columns, that wraps it. +.B ansi +draws each +.I file +into a grid the way an ANSI-BBS terminal would, following the cursor moves and +the wrap, and writes the grid out as UTF-8 lines a modern terminal shows as +the artist drew them. +.PP +The SAUCE record at the end of a file, when there is one, gives the width; a +background with the blink attribute is shown bright, as iCE colour. With no +.IR file , +or when +.I file +is +.BR \- , +.B ansi +reads standard input. +.SH OPTIONS +.TP +.BR \-p ", " \-\-plain +Write the characters only, without colour. +.TP +.BR \-m ", " \-\-mono +Write without colour, redrawing each coloured area as shading by how bright +its colour looks: bright areas as full blocks, dark ones as light shade or +space, and half blocks where the top and bottom of a cell differ. Art built +from coloured spaces keeps its shape this way, where +.B \-\-plain +would leave it blank. Useful for newsgroups and mail, which show no colour. +.TP +.BR \-w ", " \-\-width " " \fIwidth\fR +Lay the art out +.I width +columns wide instead of the SAUCE width (or 80). +.TP +.B info +Print each file's SAUCE record: title, artist, group, date and size. +.TP +.BR \-h ", " \-\-help +Show a summary of usage. +.TP +.BR \-V ", " \-\-version +Show the version. +.SH EXAMPLES +.nf +ansi piece.ans | less \-R +ansi \-\-mono piece.ans > piece.txt +ansi info *.ans +curl \-s https://16colo.rs/pack//raw/.ans | ansi +.fi +.SH EXIT STATUS +0 on success, 1 for a usage error, 2 when a file could not be read. +.SH SEE ALSO +.BR less (1), +.BR iconv (1) +.SH AUTHOR +funkpower diff --git a/ansi.c b/ansi.c new file mode 100644 index 0000000..992e1ee --- /dev/null +++ b/ansi.c @@ -0,0 +1,473 @@ +/* + * ansi - show ANSI art in a modern terminal, or turn it into plain text. + * + * An .ans file is CP437 text with ANSI escape codes, usually laid out for an + * 80-column terminal that wraps it. ansi draws it into a grid the way a BBS + * terminal would (cursor moves, wrapping, iCE colours, the SAUCE record), then + * writes the grid out as UTF-8: in colour, as plain characters, or in + * monochrome with coloured areas redrawn as shading. + */ +#define _POSIX_C_SOURCE 200809L + +#include +#include +#include +#include + +#define VERSION "1.0.0" +#define MAX_WIDTH 1000 +#define MAX_CELLS (1u << 24) /* about 80 MB of grid; art past it is dropped */ + +/* CP437 as UTF-8. 0x01-0x1F are the glyphs art uses them for, not controls. */ +static const char *const cp437[256] = { + " ", "☺", "☻", "♥", "♦", "♣", "♠", "•", + "◘", "○", "◙", "♂", "♀", "♪", "♫", "☼", + "►", "◄", "↕", "‼", "¶", "§", "▬", "↨", + "↑", "↓", "→", "←", "∟", "↔", "▲", "▼", + " ", "!", "\"", "#", "$", "%", "&", "'", + "(", ")", "*", "+", ",", "-", ".", "/", + "0", "1", "2", "3", "4", "5", "6", "7", + "8", "9", ":", ";", "<", "=", ">", "\?", + "@", "A", "B", "C", "D", "E", "F", "G", + "H", "I", "J", "K", "L", "M", "N", "O", + "P", "Q", "R", "S", "T", "U", "V", "W", + "X", "Y", "Z", "[", "\\", "]", "^", "_", + "`", "a", "b", "c", "d", "e", "f", "g", + "h", "i", "j", "k", "l", "m", "n", "o", + "p", "q", "r", "s", "t", "u", "v", "w", + "x", "y", "z", "{", "|", "}", "~", "⌂", + "Ç", "ü", "é", "â", "ä", "à", "å", "ç", + "ê", "ë", "è", "ï", "î", "ì", "Ä", "Å", + "É", "æ", "Æ", "ô", "ö", "ò", "û", "ù", + "ÿ", "Ö", "Ü", "¢", "£", "¥", "₧", "ƒ", + "á", "í", "ó", "ú", "ñ", "Ñ", "ª", "º", + "¿", "⌐", "¬", "½", "¼", "¡", "«", "»", + "░", "▒", "▓", "│", "┤", "╡", "╢", "╖", + "╕", "╣", "║", "╗", "╝", "╜", "╛", "┐", + "└", "┴", "┬", "├", "─", "┼", "╞", "╟", + "╚", "╔", "╩", "╦", "╠", "═", "╬", "╧", + "╨", "╤", "╥", "╙", "╘", "╒", "╓", "╫", + "╪", "┘", "┌", "█", "▄", "▌", "▐", "▀", + "α", "ß", "Γ", "π", "Σ", "σ", "µ", "τ", + "Φ", "Θ", "Ω", "δ", "∞", "φ", "ε", "∩", + "≡", "±", "≥", "≤", "⌠", "⌡", "÷", "≈", + "°", "∙", "·", "√", "ⁿ", "²", "■", " ", +}; + +/* How bright each of the 16 CGA colours looks (CIE L*, 0-100). */ +static const double lightness[16] = { + 0.0000, 35.0952, 60.5599, 45.6931, 19.6482, 40.3255, 63.0540, 69.6102, + 36.1459, 60.2599, 88.9731, 97.4042, 46.5096, 65.7308, 91.9852, 100.0000 +}; + +enum mode { COLOUR, PLAIN, MONO }; + +typedef struct { + unsigned char ch; /* CP437 byte; 0 is stored as a space */ + unsigned char fg, bg; /* 0-7 */ + unsigned char bold, blink; /* blink is iCE: the bright background */ +} cell; + +typedef struct { + char title[36], author[21], group[21], date[9]; + unsigned width, height, comments, flags; + unsigned char datatype, filetype; + int present; +} sauce; + +typedef struct { + cell *cells; + size_t rows, cap; + unsigned width; +} grid; + +static const char *progname = "ansi"; + +static void *xrealloc(void *p, size_t n) +{ + p = realloc(p, n); + if (!p) { + fprintf(stderr, "%s: out of memory\n", progname); + exit(2); + } + return p; +} + +static unsigned char *slurp(const char *path, size_t *len) +{ + FILE *f = strcmp(path, "-") ? fopen(path, "rb") : stdin; + if (!f) { + fprintf(stderr, "%s: %s: %s\n", progname, path, strerror(errno)); + return NULL; + } + size_t cap = 65536, n = 0; + unsigned char *buf = xrealloc(NULL, cap); + for (;;) { + size_t got = fread(buf + n, 1, cap - n, f); + n += got; + if (n < cap) + break; + buf = xrealloc(buf, cap *= 2); + } + if (ferror(f)) { + fprintf(stderr, "%s: %s: read error\n", progname, path); + free(buf); + buf = NULL; + } + if (f != stdin) + fclose(f); + *len = n; + return buf; +} + +static void field(char *dst, const unsigned char *src, size_t n) +{ + memcpy(dst, src, n); + dst[n] = '\0'; + for (size_t i = n; i > 0 && (dst[i - 1] == ' ' || dst[i - 1] == '\0'); i--) + dst[i - 1] = '\0'; +} + +static unsigned u16(const unsigned char *p) { return p[0] | p[1] << 8; } + +/* Read the SAUCE record and shorten len to the art itself. */ +static void read_sauce(const unsigned char *data, size_t *len, sauce *s) +{ + memset(s, 0, sizeof *s); + s->width = 80; + if (*len >= 128 && !memcmp(data + *len - 128, "SAUCE00", 7)) { + const unsigned char *r = data + *len - 128; + s->present = 1; + field(s->title, r + 7, 35); + field(s->author, r + 42, 20); + field(s->group, r + 62, 20); + field(s->date, r + 82, 8); + s->datatype = r[94]; + s->filetype = r[95]; + s->comments = r[104]; + s->flags = r[105]; + s->height = u16(r + 98); + if (s->datatype == 1 && s->filetype <= 1 && u16(r + 96) && u16(r + 96) <= MAX_WIDTH) + s->width = u16(r + 96); + size_t trailer = 128 + (s->comments ? 5 + 64 * s->comments : 0); + *len = *len > trailer ? *len - trailer : 0; + } + const unsigned char *eof = memchr(data, 0x1A, *len); + if (eof) + *len = eof - data; +} + +/* The cell at x, y, growing the grid to reach it; NULL past MAX_CELLS. */ +static cell *at(grid *g, unsigned x, size_t y) +{ + if (y >= MAX_CELLS / g->width) + return NULL; + if (y >= g->rows) { + size_t want = y + 1; + if (want > g->cap) { + g->cap = want * 2; + g->cells = xrealloc(g->cells, g->cap * g->width * sizeof(cell)); + } + for (size_t r = g->rows; r < want; r++) + for (unsigned c = 0; c < g->width; c++) + g->cells[r * g->width + c] = (cell){' ', 7, 0, 0, 0}; + g->rows = want; + } + return &g->cells[y * g->width + x]; +} + +/* Lay the art out in a grid, the way an ANSI-BBS terminal of the given width would. */ +static void render(grid *g, const unsigned char *d, size_t n) +{ + unsigned x = 0, sx = 0, w = g->width; + size_t y = 0, sy = 0; + unsigned char fg = 7, bg = 0, bold = 0, blink = 0; + + for (size_t i = 0; i < n;) { + unsigned char b = d[i]; + if (b == 0x1B && i + 1 < n && d[i + 1] == '[') { + size_t j = i + 2, ps = j; + while (j < n && d[j] >= 0x30 && d[j] <= 0x3F) + j++; + size_t pe = j; + while (j < n && d[j] >= 0x20 && d[j] <= 0x2F) + j++; + if (j >= n || d[j] < 0x40 || d[j] > 0x7E) + break; /* a broken sequence ends the art */ + unsigned char cmd = d[j]; + i = j + 1; + if (pe > ps && d[ps] == '?') + continue; /* private modes, such as line wrap */ + unsigned p[16], np = 0; + if (pe > ps) { + p[0] = 0; + np = 1; + for (size_t k = ps; k < pe; k++) { + if (d[k] == ';') { + if (np < 16) + p[np++] = 0; + } else if (d[k] >= '0' && d[k] <= '9' && np <= 16) { + p[np - 1] = p[np - 1] * 10 + (d[k] - '0'); + } + } + } + unsigned arg = np && p[0] ? p[0] : 1; + switch (cmd) { + case 'm': + if (!np) + p[np++] = 0; + for (unsigned k = 0; k < np; k++) { + unsigned v = p[k]; + if (v == 0) + fg = 7, bg = 0, bold = 0, blink = 0; + else if (v == 1) + bold = 1; + else if (v == 5) + blink = 1; + else if (v == 22) + bold = 0; + else if (v == 25) + blink = 0; + else if (v >= 30 && v <= 37) + fg = v - 30; + else if (v == 39) + fg = 7; + else if (v >= 40 && v <= 47) + bg = v - 40; + else if (v == 49) + bg = 0; + } + break; + case 'C': x = x + arg < w ? x + arg : w; break; + case 'D': x = x > arg ? x - arg : 0; break; + case 'A': y = y > arg ? y - arg : 0; break; + case 'B': y += arg; break; + case 'H': + case 'f': + y = (np && p[0] ? p[0] : 1) - 1; + x = (np > 1 && p[1] ? p[1] : 1) - 1; + if (x > w - 1) + x = w - 1; + break; + case 's': sx = x, sy = y; break; + case 'u': x = sx, y = sy; break; + case 'J': + if (arg == 2) + g->rows = 0, x = 0, y = 0; + break; + } + continue; + } + i++; + if (b == '\r') { + x = 0; + } else if (b == '\n') { + x = 0, y++; + } else if (b == 0x1B) { + /* a lone escape */ + } else { + unsigned count = b == '\t' ? 8 - x % 8 : 1; + unsigned char ch = b == '\t' || b == 0 ? ' ' : b; + while (count--) { + if (x >= w) + x = 0, y++; /* wrap only when the next character arrives */ + cell *c = at(g, x, y); + if (c) + *c = (cell){ch, fg, bg, bold, blink}; + x++; + } + } + } +} + +static int same(const cell *a, const cell *b) +{ + return a->fg == b->fg && a->bg == b->bg && a->bold == b->bold && a->blink == b->blink; +} + +static int level(double l) +{ + return l < 15 ? 0 : l < 40 ? 1 : l < 60 ? 2 : l < 85 ? 3 : 4; +} + +/* How much of a cell the foreground covers, top half and bottom half; -1 if not a block. */ +static double cover(unsigned char ch, int half) +{ + switch (ch) { + case ' ': return 0; + case 0xDB: return 1; /* full block */ + case 0xDF: return half ? 0 : 1; /* upper half */ + case 0xDC: return half ? 1 : 0; /* lower half */ + case 0xDD: case 0xDE: return .5; /* left and right halves */ + case 0xB0: return .25; + case 0xB1: return .5; + case 0xB2: return .75; + default: return -1; + } +} + +/* One character standing in for a coloured cell: shading by brightness, half blocks for halves. */ +static const char *mono(const cell *c) +{ + static const char *const shade[5] = {" ", "░", "▒", "▓", "█"}; + if (cover(c->ch, 0) < 0) + return cp437[c->ch]; + double f = lightness[c->fg + 8 * c->bold], b = lightness[c->bg + 8 * c->blink]; + int top = level(cover(c->ch, 0) * f + (1 - cover(c->ch, 0)) * b); + int bot = level(cover(c->ch, 1) * f + (1 - cover(c->ch, 1)) * b); + if (top - bot >= 2) + return "▀"; + if (bot - top >= 2) + return "▄"; + return shade[top > bot ? top : bot]; +} + +static void emit(const grid *g, enum mode m, FILE *out) +{ + /* Lines are built first so that trailing blank ones can be dropped. */ + char **lines = xrealloc(NULL, (g->rows + 1) * sizeof *lines); + size_t nlines = 0; + for (size_t y = 0; y < g->rows; y++) { + const cell *row = &g->cells[y * g->width]; + unsigned len = g->width; + while (len && row[len - 1].ch == ' ' && !row[len - 1].bg && !row[len - 1].blink) + len--; + size_t cap = 64 + len * 24, n = 0; + char *s = xrealloc(NULL, cap); + const cell *last = NULL; + for (unsigned x = 0; x < len; x++) { + const cell *c = &row[x]; + const char *glyph = m == MONO ? mono(c) : cp437[c->ch]; + if (m == COLOUR) { + int keep = last && (same(c, last) || + (c->ch == ' ' && c->bg == last->bg && c->blink == last->blink)); + if (!keep) { + n += sprintf(s + n, "\033[0;%s%d;%dm", c->bold ? "1;" : "", + 30 + c->fg, (c->blink ? 100 : 40) + c->bg); + last = c; + } + } + size_t gl = strlen(glyph); + memcpy(s + n, glyph, gl); + n += gl; + } + if (m == COLOUR && len) + n += sprintf(s + n, "\033[0m"); + else + while (n && s[n - 1] == ' ') + n--; + s[n] = '\0'; + lines[nlines++] = s; + } + while (nlines && !*lines[nlines - 1]) + free(lines[--nlines]); + for (size_t i = 0; i < nlines; i++) { + fputs(lines[i], out); + fputc('\n', out); + free(lines[i]); + } + free(lines); +} + +static void info(const char *path, const sauce *s, const grid *g, FILE *out) +{ + static const char *const types[] = {"ASCII", "ANSi", "ANSiMation"}; + fprintf(out, "%s\n", path); + if (!s->present) { + fprintf(out, " no SAUCE record; laid out at %u columns, %zu row%s\n", g->width, g->rows, + g->rows == 1 ? "" : "s"); + return; + } + if (*s->title) fprintf(out, " title %s\n", s->title); + if (*s->author) fprintf(out, " author %s\n", s->author); + if (*s->group) fprintf(out, " group %s\n", s->group); + if (strlen(s->date) == 8) + fprintf(out, " date %.4s-%.2s-%.2s\n", s->date, s->date + 4, s->date + 6); + fprintf(out, " size %ux%u", s->width, s->height ? s->height : (unsigned)g->rows); + if (s->datatype == 1 && s->filetype <= 2) + fprintf(out, ", %s", types[s->filetype]); + if (s->flags & 1) + fprintf(out, ", iCE colours"); + fputc('\n', out); +} + +static void usage(FILE *out) +{ + fprintf(out, + "usage: %s [-p | -m] [-w WIDTH] [FILE...]\n" + " %s info FILE...\n" + "\n" + "Show ANSI art (CP437 with ANSI colour codes, as .ans files are) in a UTF-8\n" + "terminal, laid out the way a BBS terminal would draw it. With no FILE, or\n" + "when FILE is -, it reads standard input.\n" + "\n" + " -p, --plain the characters only, no colour\n" + " -m, --mono no colour, with coloured areas redrawn as shading by\n" + " brightness (for newsgroups and mail that show no colour)\n" + " -w, --width N lay the art out N columns wide (default: SAUCE, else 80)\n" + " info print each file's SAUCE record: title, artist, size\n" + " -h, --help show this help\n" + " -V, --version show the version\n" + "\n" + "Examples:\n" + " %s piece.ans | less -R\n" + " %s --mono piece.ans > piece.txt\n", + progname, progname, progname, progname); +} + +int main(int argc, char **argv) +{ + enum mode m = COLOUR; + unsigned width = 0; + int show_info = 0, status = 0, files = 0; + + for (int i = 1; i < argc; i++) { + const char *a = argv[i]; + if (!strcmp(a, "-h") || !strcmp(a, "--help") || !strcmp(a, "help")) { + usage(stdout); + return 0; + } else if (!strcmp(a, "-V") || !strcmp(a, "--version")) { + printf("%s %s\n", progname, VERSION); + return 0; + } else if (!strcmp(a, "-p") || !strcmp(a, "--plain")) { + m = PLAIN; + } else if (!strcmp(a, "-m") || !strcmp(a, "--mono")) { + m = MONO; + } else if (!strcmp(a, "-w") || !strcmp(a, "--width")) { + if (++i >= argc || (width = (unsigned)strtoul(argv[i], NULL, 10)) < 1 || width > 1000) { + fprintf(stderr, "%s: --width needs a number from 1 to 1000\n", progname); + return 1; + } + } else if (!strcmp(a, "info") && files == 0 && !show_info) { + show_info = 1; + } else if (a[0] == '-' && a[1]) { + fprintf(stderr, "%s: unknown option %s\n", progname, a); + usage(stderr); + return 1; + } else { + argv[++files] = argv[i]; /* keep the file names at the front */ + } + } + if (!files) + argv[++files] = "-"; + + for (int f = 1; f <= files; f++) { + size_t len; + unsigned char *data = slurp(argv[f], &len); + if (!data) { + status = 2; + continue; + } + sauce s; + read_sauce(data, &len, &s); + grid g = {NULL, 0, 0, width ? width : s.width}; + render(&g, data, len); + if (show_info) + info(argv[f], &s, &g, stdout); + else + emit(&g, m, stdout); + free(g.cells); + free(data); + } + return status; +}