IMGEditor: Building an Archive Editor for Rockstar 3D Era Games

What is IMGEditor?

IMGEditor is a desktop application for editing IMG archive files — the container format used by Rockstar's 3D era games. These archives hold textures, models, and other game assets.

The IMG Format

The IMG format is a simple archive structure:

• Header — contains metadata and file count
• File table — offsets and sizes of each entry
• Data — the actual file contents packed sequentially

struct IMGHeader {
    char magic[4];      // "VER2"
    uint32_t numEntries;
    uint32_t dirOffset;
    uint32_t dirSize;
};

Building the Editor

I chose C++ with ImGui for the UI because:

1. Native performance — large archives need fast I/O
2. Cross-platform potential — ImGui works on Windows, Linux, Mac
3. Familiar stack — I already knew C++ well
4. Clean UI — ImGui provides a professional look with minimal effort

Features

• Import/Export individual files or bulk operations
• Preview textures directly in the editor
• Drag and drop support for easy file management
• Batch replacement for modders updating multiple assets
• Backup system to prevent accidental data loss

Multi-Game Support

The biggest challenge was supporting multiple game variants. Each game uses slightly different versions of the format, so I implemented a version detection system:

enum class IMGVersion {
    GTA3,      // Original format
    VC,        // Vice City variant
    SA,        // San Andreas (most common)
    Bully,     // Bully Scholarship Edition
    Unknown
};

IMGVersion DetectVersion(const char* header) {
    // Analyze header structure to determine version
    // ...
}

Results

IMGEditor has been downloaded thousands of times and is used by modders worldwide. It's become an essential tool in the GTA modding toolkit.