Hi there,

I'm posting here for the first time, so let me know if I mess anything up!

I'm really interested in learning how to understand some of the binary representations of the sims 4 packages. Of special interest is the MLOD chunk. Over on this forum a treasure snippet was posted by the simgurumodsquad in response to Cmarinetti's request for a .bt file of the new MLOD chunk.

https://forums.thesims.com/en_US/di...mlod-0x01d10f34 (snippet follows)
```

//
// MLOD block
//

typedef struct
{
UINT32 mState;
UINT32 mStartIndex;
UINT32 mMinVertexIndex;
UINT32 mVertexCount;
UINT32 mPrimitiveCount;
} PrimitiveInfoForState;

typedef struct
{
FLOAT min[3];
FLOAT max[3];
} BoundingBox;

typedef struct(int version)
{
UINT32 mMeshLength;
local int nextBlock = FTell() + mMeshLength;

UINT32 mHashedName <format=hex>;
UINT32 mMaterialRef <format=hex>;
UINT32 mVertexFormatRef <format=hex>;
UINT32 mVertexBufferRef <format=hex>;
UINT32 mIndexBufferRef <format=hex>;
UINT32 mPrimitiveType : 8 <format=hex>;
UINT32 mMeshFlags : 24 <format=hex>;
UINT32 mStreamOffset;
UINT32 mStartVertex;
UINT32 mStartIndex;
UINT32 mMinVertexIndex;
UINT32 mVertexCount;
UINT32 mPrimitiveCount;
BoundingBox mBoundingBox;
INT32 mSkinRef;
UINT32 mBoneCount;

if (mBoneCount>0)
{
UINT32 mBoneHash[mBoneCount];
}

UINT32 mMeshMaterial <format=hex>;

UINT32 mNumPrimInfo;
if ( mNumPrimInfo > 0 )
{
PrimitiveInfoForState mPrimitiveInfoForState[mNumPrimInfo];
}
UINT32 mParentBone <format=hex>;
float mMirrorPlane[4];
UINT32 mSortOrderHint;

if (version >= 0x206 && (mMeshFlags & 0x4000) && mBoneCount > 0)
{
// Bone local bounding boxes
BoundingBox mBoundingBoxBones[mBoneCount];
}

if (FTell()!= nextBlock)
{
Warning("Not all data read from MLOD.");
return -1;
}

} MeshDiskFormat;

typedef struct
{
BlockSignature mMLODSignature; // MLOD
UINT32 mVersion <format=hex>;
UINT32 mMeshCount;
MeshDiskFormat mMeshData(mVersion)[mMeshCount] <optimize=false>;
} MLOD;
```
Almost everything works for me, except that they include this thing ` BlockSignature mMLODSignature; // MLOD` towards the bottom which doesn't appear to be defined anywhere in the file.

I followed as much of this as I could understand (https://modthesims.info/wiki.php?title=Sims_4:RCOL), but I think my imhex pattern showed I didn't have it quite right (see the imhex screenshot), and some things that should have non-zero chunksize were still 0 which was a pretty good indication I was on the wrong track.


Can anyone help me understand how the MLOD chunk header/signature is defined?

Thanks for any info that can be shared!