printimage.c

/*bin/echo  ' -*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;coding:utf-8 -*-┤
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ To the extent possible under law, Justine Tunney has waived                  │
│ all copyright and related or neighboring rights to this file,                │
│ as it is written in the following disclaimers:                               │
│   • http://unlicense.org/                                                    │
│   • http://creativecommons.org/publicdomain/zero/1.0/                        │
╚────────────────────────────────────────────────────────────────────'>/dev/null
  if ! [ "${0%.*}.exe" -nt "$0" ]; then
    cc -O -o "${0%.*}.exe" "$0" || exit
  fi
  exec "${0%.*}.exe" "$@"
  exit

OVERVIEW

  Simple Terminal Image Printer

AUTHOR

  Justine Tunney <jtunney@gmail.com>

DESCRIPTION

  This program demonstrates a straightforward technique for displaying
  PNG/GIF/JPG/etc. files from the command line. This program supports
  xterm256 and 24-bit color w/ UNICODE half blocks. For example:

    apt install build-essential imagemagick
    ./printimage.c lemur.png

NOTES

  More advanced techniques exist for (1) gaining finer detail, as well
  as (2) reducing the number of bytes emitted; this program is here to
  get you started. */

#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <termios.h>
#include <unistd.h>

#define SQR(X) ((X) * (X))
#define UNCUBE(x) x < 48 ? 0 : x < 115 ? 1 : (x - 35) / 40
#define ORDIE(X)                   \
  do {                             \
    if (!(X)) perror(#X), exit(1); \
  } while (0)

static int want24bit_;

/**
 * Quantizes 24-bit RGB to xterm256 code range [16,256).
 */
int rgb2xterm256(int r, int g, int b) {
  unsigned char cube[] = {0, 0137, 0207, 0257, 0327, 0377};
  int av, ir, ig, ib, il, qr, qg, qb, ql;
  av = r * .299 + g * .587 + b * .114 + .5;
  ql = (il = av > 238 ? 23 : (av - 3) / 10) * 10 + 8;
  qr = cube[(ir = UNCUBE(r))];
  qg = cube[(ig = UNCUBE(g))];
  qb = cube[(ib = UNCUBE(b))];
  if (SQR(qr - r) + SQR(qg - g) + SQR(qb - b) <=
      SQR(ql - r) + SQR(ql - g) + SQR(ql - b)) {
    return ir * 36 + ig * 6 + ib + 020;
  } else {
    return il + 0350;
  }
}

/**
 * Prints raw packed 8-bit RGB data from memory.
 */
void PrintImage(int yn, int xn, unsigned char rgb[yn][xn][3]) {
  unsigned y, x;
  for (y = 0; y < yn; y += 2) {
    if (y) printf("\r\n");
    for (x = 0; x < xn; ++x) {
      if (want24bit_) {
        printf("\033[48;2;%hhu;%hhu;%hhu;38;2;%hhu;%hhu;%hhum▄",
               rgb[y + 0][x][0], rgb[y + 0][x][1], rgb[y + 0][x][2],
               rgb[y + 1][x][0], rgb[y + 1][x][1], rgb[y + 1][x][2]);
      } else {
        printf("\033[48;5;%hhu;38;5;%hhum▄",
               rgb2xterm256(rgb[y + 0][x][0],
                            rgb[y + 0][x][1],
                            rgb[y + 0][x][2]),
               rgb2xterm256(rgb[y + 1][x][0],
                            rgb[y + 1][x][1],
                            rgb[y + 1][x][2]));
      }
    }
  }
  printf("\033[0m\r");
}

/**
 * Determines dimensions of teletypewriter.
 */
void GetTermSize(int *out_rows, int *out_cols) {
  struct winsize ws;
  ws.ws_row = 20;
  ws.ws_col = 80;
  ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws);
  ioctl(STDIN_FILENO, TIOCGWINSZ, &ws);
  *out_rows = ws.ws_row;
  *out_cols = ws.ws_col;
}

void ReadAll(int fd, char *p, size_t n) {
  ssize_t rc;
  size_t got;
  do {
    ORDIE((rc = read(fd, p, n)) != -1);
    got = rc;
    if (!got && n) {
      fprintf(stderr, "error: expected eof\n");
      exit(EXIT_FAILURE);
    }
    p += got;
    n -= got;
  } while (n);
}

unsigned char *LoadImageOrDie(char *path, int yn, int xn) {
  size_t size;
  void *rgb;
  char dim[10 + 1 + 10 + 1 + 1];
  int pid, wstatus, readwrite[2];
  sprintf(dim, "%ux%u" /* jfc */ "!", xn, yn);
  pipe(readwrite);
  if (!(pid = fork())) {
    close(readwrite[0]);
    dup2(readwrite[1], STDOUT_FILENO);
    execvp("convert", /* apt install imagemagick */
           (char *const[]){"convert", path, "-resize", dim, "-colorspace",
                           "RGB", "-depth", "8", "rgb:-", NULL});
    _Exit(EXIT_FAILURE);
  }
  close(readwrite[1]);
  ORDIE((rgb = malloc((size = yn * xn * 3))));
  ReadAll(readwrite[0], rgb, size);
  ORDIE(close(readwrite[0]) != -1);
  ORDIE(waitpid(pid, &wstatus, 0) != -1);
  ORDIE(WEXITSTATUS(wstatus) == 0);
  return rgb;
}

int main(int argc, char *argv[]) {
  void *rgb;
  int i, yn, xn;
  setlocale(LC_ALL, "C.UTF-8");
  GetTermSize(&yn, &xn);
  yn *= 2;
  for (i = 1; i < argc; ++i) {
    if (strcmp(argv[i], "-t") == 0) {
      want24bit_ = 1;
    } else {
      rgb = LoadImageOrDie(argv[i], yn, xn);
      PrintImage(yn, xn, rgb);
      free(rgb);
    }
  }
  return 0;
}

How can the aspect ratio be preserved (while still fitting in the 'box' of the terminal?
Either by the width not going full so the height fits, or going full width while the top part of the image has scrolled off the terminal window..?