/* This script os meant to convert a 256x256 pixel bitmap into an bitmap of
 * 8x8 pixel characters. When deciding upon the output format, i had the
 * video output of scanlines in mind. So there are 8 sections for each row
 * of pixels for a character cell, each secton containing the the pixel line
 * data of all 256 character codes. If you align this blob to 256-bytes, you
 * quickly fetch the data by pointing bx to the begin of the section for the
 * pixel line you are currently drawing, then set bl to the character value
 * you want to print and dereference [bx].
 */

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>

FILE* in;
FILE* out;
void *addr;

void copyline(int c) {
  uint8_t *ptr = addr + 0x82 + (128/8)*(127 - c);
  int i;
  for (i=0; i<16; i++) {
    fputc(*ptr++, out);
  }
}

int main(int argc, char** argv) {
  struct stat sbuf;

  in = fopen(argv[1], "r+");
  out = fopen(argv[2], "w");

  fstat(fileno(in), &sbuf);

  if (sbuf.st_size != 2178) {
    printf("File must be a 128x128 pixel 1 bit monochrome bmp\n");
    exit(1);
  }

  addr = mmap(NULL, sbuf.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fileno(in), 0);

  int i, j;
  for(j=0; j<8; j++) {
    for(i=0; i<16; i++) {
      copyline(j+i*8);
    }
  }
}