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Modding Birthright: The Gorgon's Alliance
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October 11, 2024
In my last post, I mentioned that the main Doom map editors don’t have any way of loading Birthright textures. This can be fixed by creating a PWAD with all of the textures from TEXTURES.RES. As I shared in The Case of the Missing PCX Palettes, we’re able to submit PCX files to Birthright’s resource files, but we’re not able to get them back out in their original state. A lot of information is lost when RESUTIL or BRUT convert the PCX files into Birthright’s internal bitmap format.
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October 7, 2024
Implementing LZSS compression in BRUT is still on my task list. I’ve written out a first draft of the algorithm, which is giving me some trouble. I hope to get that implemented soon. Since I’ve been staring at assembly language far too much, I decided to dig deeper into what we know about Birthright’s adventures, especially how they’re defined, referenced, and loaded. In the future, I’ll build a reference page to make finding some of the technical information necessary for proper level building easier.
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September 15, 2024
The BRUT project is now nearing feature parity with the original RESUTIL application, which feels fantastic. So far, the changes made by BRUT are identical to those made by RESUTIL on a binary level. The only missing feature is LZSS compression. As the test below demonstrates, overriding resources without LZSS compression is still possible.
The video is a little choppy, but that really shouldn’t be related to the compression since the game would need to decompress the images to display them anyway.
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September 2, 2024
Today, I learned that I am not only much closer to a working decompression algorithm than I thought, but I also made a very bad assumption when starting this project—one that I could have avoided with a little more preparation.
When I start a project from scratch or start working on something at work, I plan things out beforehand. I make sure I understand the scope of the work as fully as I can before I write any code.
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August 29, 2024
I’ve made far less progress than I was hoping. Part of the delay is just being busy with life. The algorithm isn’t really that complicated. There are some technical things about assembly language that I’ve had to relearn, like how the EFLAGS register works with bitshifting. (Specifically, the carry flag (CF) is relevant to this algorithm.) I also watched a great lecture on LZSS to understand the basics of what the algorithm was likely to do.
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August 19, 2024
I’ve spent two or three days working on the Birthright Resource Utility (BRUt) and have managed to implement displaying the file index and exporting uncompressed files. Unfortunately, I’ve run into a bit of a problem with extracting compressed files.
For context, the resource files on the Birthright CD contain a total of 9427 files, of which 125 files (1.3%) are uncompressed. This leaves 98.7% of files unextractable. This makes the tool effectively useless.
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August 14, 2024
For several years there has been a thread on the Birthright.net forums talking about modding Birthright: The Gorgon’s Alliance. The posts have been few and far between, but there does seem to be some interest into adding new adventures to the game.
The work that’s been done there has discovered that Birthright adventures are pieced together through a combination of resource files (.RES) in the RESFILES directory, descriptions in the TEXT directory, and level information in the WADS directory.