3D Scene Hierarchy (.3dd files)

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This file is based on the Segments format

The purpose of this file format is to serialize the hierarchy (scene graph) of 3d models and referencing raw geometry data in 3dg files. Thus it most notably does not contain geometry data and one always additionally needs a 3dg file for that.

Segments

Hierarchy Segment

The hierarchy segment is the outermost segment, the one that needs to be inspected first. It is wrapped in a HIEA parent segment and the children are HIE..

struct HierarchySegment {
    uint Zero;
    // The offset (pointer) to the instance segment
    uint OffsetInstance;
    // "number in branch", whatever that means.
    ushort NumInBranch;
    ushort Unk1;
    // The offset (pointer) to the parent hierarchy segment
    uint OffsetParent;
}

In order to build a scene hierarchy, one needs to evaluate the OffsetParent. Hierarchy segments aren’t deeply nested in the file structure, instead they are all siblings in the HIEA segment. Thus, OffsetParent has to be compared to the Position of each segment, where OffsetParent = 0 denotes the root node.

When the hierarchy is done, hierarchy segments can be linked to instance segments by using OffsetInstance in a similar way.

Instance Segment

struct InstanceSegment {
    struct LOD
    {
        uint OffsetObj;
        // Range *within* the LoD is displayed. 0.0 => always
        float Range;
        uint Zeroes1;
        uint Zeroes2;
        uint Zeroes3;
    }

    byte[] Matrix; // 64 Bytes

    uint Zero1;
    uint OffsetMBNK;
    int Type; // 0 == dummy node, otherwise -1 (?)
    ushort Unk1;
    ushort NbOfLods;
    LOD[] Lods;
}

An instance of a geometry has a transform (Matrix), a type (dummy nodes don’t have geometry, they are purely for the transform hierarchy), an offset into the MBNK segment (material reference) and a hardcoded 4 level of detail layers (size-wise, but NbOfLods determines how many of the array elements are filled).

The Level of Detail has both, a Range ^[1] and an offset at which to find Object Segments that represent the relevant geomtry for the level of detail.

Do note, that the offset does not directly point to the object segment but instead point into an entry of the Hash Segment that is a child of OBJA. The same hash name can be used for the hash segment in the GEOA segment in the 3dg file.

Object Segment

struct ObjectSegment {
    uint Zero1;
    uint Zero2;
    uint Zero3;
    uint NbOfMaterials;
    float BoundX;
    float BoundY;
    float BoundZ;
    float BoundRadians;
}

The object segment mainly consits of a number of materials and a bounding box. ^[2]

Material Bank Segment

struct MBnkSegment {
    struct MBnkEntry {
        String8 Name;
        ulong Unk; // an offset?
    }

    MBnkEntry[] Entries;
}

1. Clarify if >= or ⇐

2. Clarify, what the radians bound means