cc-stuff/cpi2png.c

// x-run: make test-cpi2png

#include <assert.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <stb/stb_image.h>
#include <stb/stb_image_write.h>
#include <string.h>

#include "cc-common.h"

bool read_varint(FILE *fp, unsigned int *out);

int main(int argc, char **argv) {
  if (argc < 3) {
    fprintf(stderr, "Usage: %s [input.cpi] [output.png]\n", argv[0]);
  }

  FILE *fp_in = fopen(argv[1], "rb");
  assert(fp_in != NULL && "Failed to open input file");

  unsigned char header[4];

  unsigned char version = 0;
  assert(fread(header, 1, 4, fp_in) == 4 && "Failed to read header: not enough bytes");
  if (0 == memcmp(header, "CCPI", 4)) { // Original CCPI (CPIv0)
    version = 0;
  } else if (0 == memcmp(header, "CPI", 3)) { // Newer CCPI (CPIvX)
    version = header[3];
  } else {
    assert(false && "Not a CPI/CCPI image: invalid header");
  }

  if (version & 0x80) {
    fprintf(stderr, "Draft version: 0x%02x may not be supported properly! Here be dragons!\n", version);
  }

  unsigned int width = 0, height = 0;

  if (version == 0) {
    width = fgetc(fp_in);
    height = fgetc(fp_in);
    (void)fgetc(fp_in); // XXX: ignore scale
  } else if (version == 1) {
    assert(read_varint(fp_in, &width) && "Failed to read width varint");
    assert(read_varint(fp_in, &height) && "Failed to read height varint");
  } else {
    assert(false && "Failed to read size: unsupported version");
  }

  union color *canvas = malloc(width * height * 8 * 11 * sizeof(union color));


  // XXX: may change in future when we introduce variable-size palettes
  // though, it may never change, if I'm being honest. Why would I choose
  // worse image quality with less colors when I can use all of them?
  union color *colors = calloc(16, sizeof(union color));

  // NOTE: our `union color` type is 4 bytes long, while palette stored in the
  // file itself uses 3 bytes per color, so we can't just `fread` them at once,
  // sadly.
  for (int i = 0; i < 16; i++) {
    colors[i].rgba.r = fgetc(fp_in);
    colors[i].rgba.g = fgetc(fp_in);
    colors[i].rgba.b = fgetc(fp_in);
    colors[i].rgba.a = 0xff;
  }

  for (int y = 0; y < height; y++) {
    for (int x = 0; x < width; x++) {
      unsigned char sym = fgetc(fp_in);
      unsigned char color = fgetc(fp_in);
      union color background = colors[color & 0xF];
      union color foreground = colors[color >> 4];
      for (int oy = 0; oy < 11; oy++) {
        for (int ox = 0; ox < 8; ox++) {
          union color pix = ((0x80 >> ox) & cc_font_atlas[sym][oy]) ? foreground : background;
          canvas[ox + (x + (y * 11 + oy) * width) * 8] = pix;
        }
      }
    }
  }

  stbi_write_png(argv[2], width * 8, height * 11, 4, canvas, 0);

  free(colors);
  free(canvas);
  fclose(fp_in);
  return EXIT_SUCCESS;
}

bool read_varint(FILE *fp, unsigned int *out) {
  int position = 0;

  while (true) {
    unsigned char curr = fgetc(fp);
    *out |= (curr & 0x7F) << position;

    if ((curr & 0x80) == 0) break;

    position += 7;

    if (position >= 32) return false;
  }

  return true;
}