progmem.c

void draw_character(font_t* font, uint8_t x, uint8_t y, char chr) {
  for (uint8_t cy=0; cy < 8; cy++) {
    for (uint8_t cx=0; cx < 8; cx++) {
      uint8_t d = (y + cy) % 8;
      uint8_t* b = &gfx_buffer[((y + cy) / 8 * 128) + x + cx];

      uint8_t** flash_data = pgm_read_word(&font->data);
      uint8_t* chr_data = pgm_read_word(&flash_data[chr]);

      if (pgm_read_byte(&chr_data[7 - cy]) & (0x01 << cx)) {
        *b |= 0x80 >> d;
      } else {
        *b &= ~(0x80 >> d);
      }
    }
  }
}