Cars: Race-O-Rama Shaders

A shader decompilation project for Cars: Race-O-Rama (Xbox 360).

Overview

This repository aims to decompile the Xenos shaders used in the Xbox 360 version of Cars: Race-O-Rama back into HLSL source code that matches 1:1 with the original game's logic. The shaders are compiled using the Xbox 360 version of the fxc shader compiler found in XDK 8276, to match the exact version used by the original developers. This project aims to produce byte-matching .vsh and .psh files.

The reason why this project exists is so that these shaders can later be refactored to work on Windows and ported into the PC version of Cars: Mater-National Championship, as currently, there are numerous issues with the way scenes ported from Cars: Race-O-Rama appear visually. Understanding the way this game's shaders work will help tremendously with modding Cars: Mater-National Championship.

- source/          # Contains the HLSL source files.
- compiled/        # Contains the compiled versions of the source .hlsl shaders in `.vsh`/`.psh` format.
- target/          # Contains the original game's target .vsh/.psh binaries.
- asm/generated/   # Dissasembly output for the non-matching shaders in compiled/.
- asm/reference/   # Dissasembly output for the originial games' shaders in target/.
- CompileAll.py    # Script to automatically compile all shaders in the source/ folder and output them to the compiled/ folder.
- Verify.py        # Script to automatically identify matched shaders and dump dissassembly output to asm/generated/ and asm/reference/ as needed.

Workflow

To decompile a shader, a specific .vsh/.psh file is chosen from the target folder, and it's .hlsl source file inside the source/ folder is modified and permuted until it matches the target binary after CompileAll.py is ran. More specifically:

• 1. Run Verify.py to gauge current progress and find a shader to decompile that isn't missing.
• 2. Find that shader's .hlsl file in source/, and the target assembly in asm/reference/.
• 3. Analyze the reference assembly and recover the original logic, then transplant it into the .hlsl file.
• 4. Run CompileAll.py, or manually compile the shader with fxc-xbox-8276 (with the proper arguments as outlined in CompileAll.py), then run Verify.py to check the results.
• 5. If the shader is now matched, you're done. If not, check the generated assembly in asm/generated/ and compare it against the target asm/reference/, permute the .hlsl source again, and repeat steps 3-5 until the shader is matched.

Requirements

• The Xbox 360 version of fxc, from XDK 8276. (fxc-xbox-8276)
• The Xbox Shader Disassembler from XDK 8276. (xsd)
• Python 3.x

Technical Details

Shader Model

• Vertex Shader Profile: vs_3_0
• Pixel Shader Profile: ps_3_0
• Platform: Xbox 360/Xenos ATI GPU