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REternal Daughter v 1.0.0


REternal Daughter is a reverse engineering project for a freeware video game Eternal Daughter. It attempts to fix issues with running the game on modern machines.

Eternal Daughter is a metroidvania (open world 2D platformer) by Blackeye Software (Derek Yu and Jon Perry). It was released as freeware in 2002. More information about the game can be found in [this article written by the author of REternal Daughter] (

REternal Daughter can run the game in a window. It is als able to run the game in a supported 640x480 resolution without upscaling (game as a 'window' within a black screen or surrounded by screen borders stored in img.bmp file). Experimental upscaling feature can be enabled by a -u command line switch, although it has issues with levels smaller than 640x480 (see below). Compared to the original game, it uses a newer version of Cncs232.dll which may fix some of the issues related to MIDI playback.

REternal Daughter also includes a save editor It's still incomplete but the most important features are there.

Issues with Eternal Daughter

Eternal Daughter runs natively in a 320x240 resolution which is too low for modern GPUs. It also has problems with its MIDI playback functions as if a music track changes while a sound effect is playing, the sound effect will loop endlessly and the game will become unplayably slow.

Usage: I just want to play the damn game already!

If you want a version of Eternal Daughter that will work on modern computers and can't be bothered with all that reverse engineering stuff, [just download that file and you're good to go] ( This is a collection of pre-patched binaries with an easy to use launcher that should work out of the box.

If you want to know more, customize the patches, edit savefiles or maybe even try a bit of reverse engineering yourself, read on. Keep in mind that while there are no prerequisites to running the pre-patched version, everything else requires you to have Python 3 with the following packages installed:

  • hy
  • bsdiff4


To use REternal Daughter, copy its files to your Eternal Daughter directory and run If you don't have the game, it can be freely downloaded from here.

usage: [-h] [-i INPUT] [-u] [-b] [-N] [-p PATCHFILE] [-n] [-r]

Unofficial Eternal Daughter patch. Default settings work if placed in the
game's folder.

optional arguments:
  -h, --help            show this help message and exit
  -i INPUT, --input INPUT
                        Input file (default: "Eternal Daughter.exe")
  -u, --upscale         Upscale the game (experimental)
  -b, --borders         High resolution with screen borders (experimental;
                        overrides -u)
  -N, --noborders       Just force higher resolution (overrides -u and -b)
  -p PATCHFILE, --patchfile PATCHFILE
                        Custom patchfile in BSDiff format (overrides -u, -b
                        and -N)
  -n, --nofix           Don't fix the game, just run it (overrides -u, -b,
                        --noborders and -p)
  -r, --replace         Permanently replace input file with a patched version
                        (overrides -n)
  -c, --cncs232         Fix Cncs232.dll (you should only run this once)

Without other arguments, the game will be started in windowed mode.


usage: [-h] [-p] [-l LIFE] [-g GEMS] [-G GEMS_MAX] [-L LOCATION]
                   [-a ATTACK_POWER] [-d {0,1}] [-e {0,1,2,3,4,5}] [-H {0,1}]
                   [-M {0,1}] [-O {0,1}] [-S {0,1}]
                   [-W {knife,hammer,mojak,ozar,sigil}]

Eternal Daughter save reader/editor. Part of the REternal Daughter project. To
use, place in the game's folder or any other folder containing ED savefiles
with slot{1-3}.sav.

positional arguments:
  {1,2,3}               Save slot number

optional arguments:
  -h, --help            show this help message and exit
  -p, --print           Print information about current savefile
  -l LIFE, --life LIFE  Set life to provided value
  -g GEMS, --gems GEMS  Set current number of gems (ammo)
  -G GEMS_MAX, --gems-max GEMS_MAX
                        Set maximum number of gems
  -L LOCATION, --location LOCATION
                        Teleport to chosen savespot
  -a ATTACK_POWER, --attack-power ATTACK_POWER
                        Set attack power
  -d {0,1}, --doublejump {0,1}
                        Enable/disable double jump
  -e {0,1,2,3,4,5}, --elanduru {0,1,2,3,4,5}
                        Pick Elanduru's form (0 - no Elanduru, 5 - adult
                        Elanduru with mask)
  -H {0,1}, --hammer {0,1}
                        Enable/disable hammer
  -M {0,1}, --mojak {0,1}
                        Enable/disable Mojak
  -O {0,1}, --ozar {0,1}
                        Enable/disable Ozar's Flame
  -S {0,1}, --sigil {0,1}
                        Enable/disable Sigil
  -W {knife,hammer,mojak,ozar,sigil}, --weapon {knife,hammer,mojak,ozar,sigil}
                        Current weapon

Reversing Eternal Daughter

Binary patches

Eternal Daughter was created with an old version of Multimedia Fusion, a game engine relatively popular among indie developers for its user-friendly 'no programming' approach.

Eternal Daughter.exe info

Game logic seems to reside completely inside Eternal Daughter.exe. The game also loads a dynamic library Cncs232.dll which contains multimedia-related functionality (presumably, this includes buggy MIDI/sound effects code).

Unfortunately, Eternal Daughter.exe also contains all the game data as there are no files containing sprites or sounds anywhere in the game folder. Even worse: all that data seems to be in custom formats as Resource Hacker is unable to extract any images or music. Even strings table doesn't contain the in-game text, just standard diagnostic messages. Opening Cncs232.dll with it is similarly fruitless: it has a few bitmaps but nothing similar to game content.

Eternal Daughter.exe in Resource Hacker

Cncs232.dll in Resource Hacker

As quick google search doesn't show any way of extracting data from compiled Multimedia Fusion games, the only thing left is disassembling the game and fixing what we can. The resolution is an obvious choice: I step through game startup in OllyDbg, find the place from which resolution data is pulled and write a simple fix. I hijack the game's execution early by calling to a code cave near the end of the application's text section. In that cave, I overwrite relevant data section fragments with 640x480 (values here presented in hex), call the function that should have been called instead of my hook and return to normal flow.

Fixing resolution

This appears to be working well: the whole game is drawn in higher resolution and it looks good. Unfortunately, there are problems here and there. The minor one is that triggers in cutscenes are visible. The bigger one is that if you come from a bigger level to a smaller one, those larger portions are not redrawn and it looks stupid. You can enable this option with -u command line switch in but it's not the default.

Everything seems fine

But it doesn't work the way it should

I change my strategy: the game will run in a higher resolution but it's not going to be upscaled. I modify the executable again, this time hardcoding 640x480 in two functions that draw the window and leaving the values from the data section intact for drawing game content.

Fixing resolution: another attempt

Of course, the game now isn't really in high resolution. It's still in 320x240, it's just that the game window is bigger so the GPUs don't go crazy. It also doesn't look as well as it should but it's far less annoying than the previous version.

Not optimal but works

I then turn my fixes into a Python/Hy (Python because rapid prototyping, Hy because I like Lisp-like syntax) program. There's a lot more that can be done but I think it's a decent start. In REternal Daughter, this behavior can be enabled with a --noborders command line switch.


Non-upscaling patch wastes a lot of screen real estate, with the game being played in a small rectangle in the middle of a black screen. The simplest solution here would be to do what the developers of shmups (and other games designed for vertically-aligned arcades) do: just draw the borders around everything. Because of the issues with upscaling mode, I assume it should be easy: just draw it once inside the game's window and nothing should overwrite it.

After trying and failing to this in assembly, I decide to write a library in C++ and just call a necessary function from assembly. I then try to add the function as an import using a variety of Portable Executable editing tools. They all fail miserably so I do what every good programmer/hacker/cracker/reverser would do in this situation: I harness the power of Google, enter a carefully chosen query ('reverse engineering games') and absorb the knowledge (I ask for help on the first site that pops up in results).

A very helpful user sends me some code which starts a process and injects a DLL into it. I modify my library to do everything in the DllMain function, inject it and fail. Strangely enough, Andoryuuta (the user who sent me the injector) is able to get it to work without issues. I try to educate myself about why this might be the case and discover some articles about session separation on different versions of Windows. I write my own injector which uses NtCreateThreadEx and therefore should bypass session separation. Unfortunately, the problem lies elsewhere ad this also doesn't work, and anything that uses NtCreateThreadEx pisses off antivirus software.

I manage to do a binary patch (not unlike the upscaling one) that hooks execution and calls LoadLibraryA. Unfortunately, the borders get overwritten for some reason so I adopt the strategy proposed by Andoryuuta: spawning a thread and drawing in a loop. This looks good on screenshots but in-game there's a lot of very annoying blinking. Still, I make the most of what I have and turn some old Eternal Daughter fanart into a suitable bitmap.

Imagine this but with blinking

This behavior can be enable with -b command line switch.

Binary patching 2: Windowed Daughter

In Mastigophoran's Let's Play, he claimed to have found a way to enable windowed mode by hex editing the game's executable. While I wasn't able to get in touch with him, I contacted Azurinel, a prominent Eternal Daughter speedrunner and world record holder (spoilers, obviously). Azurinel knew the details of Mastigophoran's modifications, which are described here. With this patch, I've been able to get the game to run in windowed mode.

Eternal Window

This patch didn't enable windowed mode by default, it only fixed the non-implemented /NOF command line switch. To make my patch more standalone, I also replaced the call to GetCommandLineA with my fake function which returns a hardcoded string ending with /NOF.

Because strcat in assembly is too much work

This is the default behavior as it's the least problematic one (no additional glitches, no unused screen real estate, no blinking).

Based on the informations from Mastigophoran's pastebin, I also made a patch which upgrades Cncs232.dll to a new version. I haven't done enough testing to confirm whether it fixes all MIDI issues but if it doesn't, the project still has a lot to do.

Reversing save files

Eternal Daughter uses slotX.sav for holding saved games, where X is a number between 1 and 3. They store binary data and opening them with a hex editor gives us a hint about what to do next: the first 8 bytes contain a magic number which is a representation of ASCII string 'CNC ARRAY'.

Savefile in hex editor

'CNC Array' is the format used by Multimedia Fusion to store the engine's array objects. According to a post by Dines, user of Clickteam forums, the format works as follows:

offset  type    details
0000    ascii   "CNC ARRAY"
0009    byte    Null
000A    dword   Always '2' for some reason. Maybe version number?
000E    dword   X dimension size
0012    dword   Y dimension size
0016    dword   Z dimension size
001A    dword   Settings (see note 1)
001E    (Data chunks follow from here)

  - DATA CHUNK (number array) -
0000    dword   value of this item in the array.

This repeats for every element in the array, until it reaches
the end of the file. There is one dword per element.

  - DATA CHUNK (text array) -
0000    dword   Length of text
0004    ascii   Stored text

  - Note 1 (Flags/Settings) -
This shows the meaning of the various bits in the flag byte:

-------- -------- -------- ----gbtn
g = Global Array (1 = yes)
b = 1-Based Array (1 = yes)
t = Text Array (1 = yes)
n = Number Array (1 = yes)
- = Bit is not used.

Do note that in hex editor, byte 000A stores the value '1' while the post claims it's always '2'. This seems to confirm the poster's theory that this is a version information variable. Looking further into the file, its settings variable (001A) stores the value of 5. In binary, a DWORD representing 5 is 29 0s followed by 101. Therefore, each save is a 1-indexed array of 32-bit integers.

Through trial and error, I discovered the meanings behind some of the variables in savefile:

Offst Variable Comments -
0x1e Health -
0x22 Double jump True/false
0x3a Current gems (ammo) Can be larger than max
0x42 Hammer True/false
0x56 Max gems Can be lower than current
0x5e Mojak True/false
0x72 Current weapon 1 - knife, 2 - hammer, 3 - Mojak, 4 - Ozar, 5 - Sigil
0x76 Ozar's Flame True/false
0x7a Elanduru save icon True/false
0x8e Elanduru's form 0 - none, 1 -3 - young, 4 - adult, 5 - adult with mask
0x96 Sigil True/false
0xaa Attack power -
0xc6 Current location -

I use that knowledge to write a save editor/analyzer.


  • better upscaling (draw empty window after switching stages?)
  • find a way to stop the border image from blinking
  • add missing features to save editor


REternal Daughter was written by Maciej Miszczyk. Andoryuuta provided a lot of help with DLL injection and fixed a bug in the third patch so the border-drawing function probably wouldn't happen without him. Most of the fourth patch was made following Mastigophoran's instructions provided indirectly by Azurinel so they too deserve a mention - there wouldn't be windowed mode without them.

The picutre currently used as a border taken from a fanart gallery in this Let's Play but I don't know anything about the author beside the fact that his name is Igor. If you're the author and don't want it used here, feel free to contact me.


This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
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