Category / retrogaming

by ReWolf

Reverse engineering Mortal Kombat GRA file format (part 2)

Disclaimer: This post is aimed at retro-gaming preservation and code-archeology. All product names, trademarks, and registered trademarks are the property of their respective owners.

933 days, this is the amount of time that passed since part 1 of that blog post. I had almost all work done back in 2018, I was just missing one small detail about the palette applied to the rendered frames. Then life happened and I pretty much abandoned not only this blog but all of my side projects. Around the beginning of February  2021, I felt a sudden urge to finish that project and I dug up all of my notes and source codes and started moving forward. The sources, obviously,  didn’t meet my quality bar after all these years, but I took the time to modernize them a bit, so it is less of a shame to make them public.

Before I start, I encourage old and new readers to take a look at part 1, as this post is a continuation and it may be easier to follow along being familiar with the prior research.

One more thing that is worth mentioning that I didn’t know in 2018 is that MK1 and MK2 executables have embedded Watcom compiler symbols. I learned about it just recently when I was looking for some recent development with regard to MK reverse engineering efforts:

I didn’t use the wcdctool as the list of steps to make it work is quite long and I have most of the executable described in IDA anyway. The most important learning I took from wcdctool is the existence of wdump utility (Open Watcom Executable Image Dump Utility) that can dump all available symbols. I used that tool to apply original functions/symbols names in IDA (on top of my own naming), so I may sometimes refer to those original names, provided they are better than the one I came up with.

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by ReWolf

Reverse engineering Mortal Kombat GRA file format (part 1)

Disclaimer: This post is aimed at retro-gaming preservation and code-archeology. All product names, trademarks and registered trademarks are property of their respective owners.

GRA files are used by the PC DOS version of Mortal Kombat 1 and 2 (available on GOG) to store all kinds of graphics. There are two different types of GRA files:

  • compressed static images or animations – this is a well-defined self-contained file format that can be easily converted to the PNG/APNG/GIF, the only obstacle is compression which has to be reverse-engineered first. I’ll refer to it as cGRA and cover that format today.
  • not compressed sprites/fonts/graphic objects/UI elements – this format is kind of a mess, it just contains encoded pixel data without any metadata. All necessary information has to be scavenged from the Mortal Kombat executable (sprites offsets, width, height, palette). I’ll refer to it as uGRA and cover that format in part 2 of this blog post (still have to figure out a few things).

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by ReWolf

Reverse engineering Might and Magic III compression

I’m not quite sure how I ended up deep inside DOSBox debugger, going through 16bit assembly and recovering decompression routine used to handle MM3.CC file, but it was definitely fun. I got the game from one of the recent humble bundles and somehow (this is the part that I’m missing) I’ve found Jeff Ludwig’s page. I’ve read about his approach to modding Might and Magic III and problems related to compressed/encrypted MM3.CC data file. One of the phrases sounded like an invitation:

“It turns out that this algorithm has been a particularly tough nut to crack, and no one has come up with a viable way of decrypting the data.”

I recommend reading the whole story as his method of dealing with this problem is also great. In this post I’ll describe how I’ve handled it, in the end there will be link to the open source utility that can not only decompress, but also compress valid MM3.CC file.

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