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blitz3d-decomp

blitz3d-decomp

github.com/rehan-remadeOther9.2k26 installsUpdated 1d ago
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About blitz3d-decomp

A skill for studying Blitz3D games and porting their behavior, using B3DDecomp to recover Blitz source as a reference. It guides disassembly, system tracing, port implementation, and measured verification while setting limits for protected builds and redistribution.

Key features

  1. 01Build and run B3DDecomp
  2. 02Disassemble modules and recover Blitz source
  3. 03Trace game systems from strings and data
  4. 04Port behavior using runtime references
  5. 05Verify ports against measured values
  6. 06Follow decompilation and licensing safeguards

Use cases

  1. 01Studying an eligible Blitz3D game
  2. 02Tracing values before implementing a port
  3. 03Validating ported behavior against the original

Install

Copy the command and run it in a terminal.

$npx skills add https://github.com/rehan-remade/universal-modder --skill blitz3d-decomp

After installing, type/blitz3d-decompin Claude Code to confirm it loaded.

Bundled files

References and scripts installed along with SKILL.md.

references/
b3d-to-roblox.md
b3ddecomp-skip-failures.patch
blitz-runtime.md
scripts/roblox/
b3d_skin.py
vm_anim_data.py
vm_build.py
vm_render.py

Details

From the project README

Blitz3D decompile and port

Blitz3D games ship as one exe: the runtime in .text and the compiled game in a resource module that the runtime links at load. Ghidra on the exe shows only the runtime. The route that works: B3DDecomp disassembles the module and decompiles it to Blitz source. Then the source is the spec for the port, and the original game stays the oracle.

Keep every disassembly and decompile outside any repo (convention: ~/<game>-decomp/), and never publish them; the scripts here are fine to keep. Leave proprietary DLLs that forbid decompiling alone: their export names in the exe are enough. Journal in the mod's MODLOG.md.

Read the source when there is one: SCP: Containment Breach (Regalis11/scpcb) and its Ultimate Edition Reborn fork (Jabka666/scpcb-ue-my) are open source under CC BY-SA 3.0.

What a port may use. A port that re-expresses a game's logic, or converts its models, keyframes, textures or sounds, redistributes that game once it is published or uploaded (to Roblox too). Port only what the user has the rights to: their own game, or an openly licensed one on its terms (SCP: Containment Breach: credit it and keep the port under CC BY-SA 3.0, and check each asset's credits, since fan games mix licences). Anything else stays a private study: nothing from it is uploaded or published.

1. Tools

  • B3DDecomp (juanjp600/B3DDecomp, C#, GPL-3): clone outside the repo, then dotnet build Blitz3DDecomp.sln -c Release. It needs a .NET 8 SDK; a user-local one installs without admin (dotnet-install.ps1 -Channel 8.0 -InstallDir <dir>). Run with DOTNET_ROLL_FORWARD=Major and bin/Release/net8.0 on PATH: the decompiler starts Blitz3DDisasm by name.
  • If one function aborts the whole run, apply references/b3ddecomp-skip-failures.patch (git apply; made on commit 2b3148b): the decompiler then skips a function it can't finish, with a step5 failed line, instead of stopping.

Done when Blitz3DDecomp.exe and Blitz3DDisasm.exe build.

2. Disassemble and decompile

Blitz3DDecomp.exe <copy of game.exe> writes <game>_disasm/ (Code/ per function, Type/, Strings.txt, BuiltIn/, Libs/, BuiltInSymbols.txt), then decompiles it to <game>_decomp/. Games built from SCP: Containment Breach's code need the game's fmod.decls as a second argument (B3DDecomp's README: the shipped decls drop a parameter from FSOUND_Stream_Open).

When it still aborts, the exception names the construct. Never make a type setter silently ignore writes to get past one: the type propagation then loops forever with no output.

Protected builds: stop. Some builds are protected against this step: a modified compiler and runtime hash every function, type and builtin name (B3DDecomp stops with Unrecognized function: @_builtIn_f<garbled>; SCP: Containment Breach 2's client is built this way), or the module is encrypted. Those are protections the developer added against decompiling. Don't reverse them: tell the user and stop (skills/mod-any-game/references/safety.md). Current B3DDecomp undoes one of them by itself, without saying so: an XOR on a .b3dmod section. List the exe's sections first (objdump -h, or any PE viewer) and stop if it has one.

Done when <game>_decomp/ holds Main.bb, Functions/, Types/ and Decls/ and the run prints at most a handful of step5 failed lines.

3. Find the system

  • Strings first: an asset path or sound the system loads (grep -l StringConstant_<n> Code/*).
  • Data-driven templates: the init function stores constants into a template per item. If the game has an addon/JSON loader, it names every field.

Done when every number the port will use is traced to the line that sets it and the line that reads it.

4. Port

Read references/blitz-runtime.md before writing port code: Blitz3D's clock, Animate, CurveValue, Euler angles, Rnd and entity calls behave in ways a straight transcription gets wrong. For animated .b3d models (viewmodels, rigs, keyframes) into Roblox, follow references/b3d-to-roblox.md; its scripts are in scripts/roblox/.

Port step for step: same order, same constants, same tick. Mark every deviation in a comment with the reason. The rights rule above covers the code as much as the models.

5. Verify against the oracle

Measure the port against the decompiled numbers in the engine, not by eye: rates (shots per second at the fixed tick), durations (frames / speed / ticks per second), aim (the sight's dot on the screen centre), ammo on the server. Record each check and its result in the journal.

Done when every ported behaviour has a measured number next to the decompiled one.

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