.3DS

Introduction

3DS is the scene format of 3D Studio, Autodesk’s modelling and animation program for MS-DOS, first released in 1990 and later replaced by 3ds Max. It holds triangle meshes with texture coordinates, materials, lights, cameras and keyframe animation. Long after the DOS program, it stayed a common way to swap models between programs, and many old model libraries are in this format.

The format has tight limits from its time: each mesh holds at most 65,535 vertices and faces, because the counts are 16-bit, and texture file names follow the short MS-DOS 8.3 pattern. Autodesk never published it; what is known comes from studying the files.

Structure

A 3DS file is binary and little-endian, built from nested chunks. Each chunk starts with a 16-bit ID and a 32-bit length that includes its own 6-byte header, so a reader can skip any chunk it does not know. The whole file is one main chunk, 0x4D4D. Inside it, the editor chunk 0x3D3D holds materials (0xAFFF) and named objects (0x4000). A triangle mesh (0x4100) contains the vertex list (0x4110), the face list (0x4120) and the texture coordinates (0x4140). Keyframe animation sits in a separate chunk, 0xB000.

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