Gamedev Hub

VFS (Virtual File Systems)

A Virtual File System (VFS) abstracts the physical storage of your computer. Instead of the engine looking for a specific path like C:/Games/Data/Textures/Grass.png, it looks for a “Virtual Path” like assets://textures/grass.

1. Why every engine needs a VFS

• Asset Packing: Opening 50,000 tiny files is slow. A VFS allows you to pack them into one large .pak or .wad file, which is much faster for the OS to read.
• Modding & Patching: You can “mount” a patch folder with higher priority than the base game. If the VFS finds grass.png in the patch folder, it ignores the base version.
• Encryption & Compression: The VFS can decrypt or decompress files on-the-fly, so the rest of your code doesn’t have to worry about it.

2. Mount Point Architecture

A VFS works by managing a list of Mount Points:

1. Priority 0 (Mod): C:/Users/Mods/CoolSword/
2. Priority 1 (Patch): C:/Game/Patches/v1.1/
3. Priority 2 (Base): C:/Game/Data/base.pak

When you call VFS.Open("textures/sword.png"), the system checks each mount point in order. The first one that contains the file wins.

3. Implementation (C++ Concept)

class VirtualFileSystem {
    std::vector<IMount*> mounts;

    FileHandle Open(string path) {
        for (auto* m : mounts) {
            if (m->Exists(path)) {
                return m->Open(path); // Returns a stream from Disk or PAK
            }
        }
        return nullptr; // 404 Not Found
    }
};

4. Async Streaming

In modern open-world games, the VFS is usually Thread-Safe. You request a file, and the VFS returns a “Future” or “Task.” The data is loaded on a background thread and delivered to you when it’s ready, preventing “hitch” during gameplay.

5. Summary

• Abstraction: Decouples logic from the file system.
• Performance: Minimizes file handles and disk seeks.
• Flexibility: Makes modding and patching a core engine feature.