D3DMESH Version 1 (ERTM) format spec — Tales of Monkey Island / BttF / S&M S3

[coccofresco]

Summary

I've reverse-engineered the D3DMESH Version 1 (ERTM) format, which is currently listed as UNSUPPORTED in the version table of TelltaleGames_D3DMesh.ms. This covers:

• Tales of Monkey Island (2009) — all 5 episodes
• Back to the Future: The Game (2010-2011)
• Sam & Max Season 3: The Devil's Playhouse (2010)
• CSI: Deadly Intent / Fatal Conspiracy (2009-2010)
• Poker Night at the Inventory (2010)
• Wallace & Gromit Episode 4 (2009)

The format sits between V0.5 (Strong Bad/W&G Ep. 1-3, EarlyGameFix 4-9) and V2 (Jurassic Park). It uses the MTRE header with version byte 0x01.

What's documented

I've written a complete format specification covering:

1. TriangleSet structure — CRC hash blocks, geometry fields (mStartIndex, mNumPrimitives, mMinVertIndex, mMaxVertIndex), bounding boxes, material block, multi-texture references
2. Face index delta compression — the bitstream algorithm for T3IndexBuffer::Decompress, cross-validated PC↔iOS on multiple meshes
3. Vertex buffer chain — 16-byte headers (count + stride + type + flags), 6 buffer types (positions, normals, weights, bone IDs, UVs, tangents), raw float32 on PC
4. Multi-texture materials — first texture = diffuse, subsequent textures classified by naming convention (bmap_bump → normal, mapspec → specular, adv_meshes → lightmap)
5. D3DTX textures — DXT1/DXT3/DXT5 + RGBA8 (for normal maps), mipmap count field, pixel data at end of file
6. Triangle strip/fan extras — mTriStrips field, extra indices beyond nprim*3 encoded as strip within the same submesh

Key differences from V0.5

Feature	V0.5 (Strong Bad/W&G)	V1 (ToMI/BttF/S&M3)
Submesh name blocks	String names or hashes by EarlyGameFix	Always CRC64 hashes (12 bytes × 3)
Material texture slots	5-7 conditional slots	Sequential name_len + name references
Vertex buffer headers	Flag byte + count + length + type	count(u32) + stride(u32) + type(u32) + flags(u32) = 16 bytes
Face data	Raw face point indices	Delta-compressed bitstream (always on PC)
Vertex compression	CompressionCheck + optional	None on PC (raw float32)

Verification

• 358/358 meshes from Tales of Monkey Island EP1 parse and export correctly
• 356/358 exact submesh count match with file header
• 70/70 triangle match between PC compressed and iOS raw indices (fx_bubble)
• Full vertex coverage (5639/5639 for sk20_guybrush, zero topological anomalies)

Resources

The full specification document (written in RTB script terminology), MaxScript pseudocode for the delta decompressor and bit reader, and a Python reference implementation are available here:

Format spec: CONTRIBUTION_RTB.md

Reference implementation (Python, pure stdlib):

• export_mesh_glb.py — self-contained D3DMESH parser + glTF exporter with embedded textures
• decode_d3dtx.py — DXT1/3/5 + RGBA8 texture decoder

Repository: https://github.com/coccofresco/telltale-explorer

Delta decompression pseudocode

The core algorithm that was missing — face index delta compression:

accumulator = ReadU16()  -- first index (seed)
bodySize = ReadU32()
body = ReadBytes(bodySize)

indices = [accumulator]
bitPos = 0

while bitPos + 11 <= bodySize * 8 AND #indices < FaceCount:
    deltaWidth = ReadBits(body, bitPos, 4);  bitPos += 4
    groupCount = ReadBits(body, bitPos, 7);  bitPos += 7
    if groupCount == 0: break

    for j = 1 to groupCount:
        sign = ReadBits(body, bitPos, 1);  bitPos += 1
        magnitude = ReadBits(body, bitPos, deltaWidth);  bitPos += deltaWidth
        delta = if sign then -magnitude else magnitude
        accumulator = (accumulator + delta) AND 0xFFFF
        append(indices, accumulator)

Bit reader is LSB-first within little-endian bytes.

---

Happy to help integrate this into the MaxScript if useful.

[Lilothestitch16]

Hi. How were you able to reverse engineer those? Also are those the only games not supported for the 3ds Max Script?

[coccofresco]

Hi :)
The main breakthrough was finding that the iOS build of ToMI ships with fully unstripped debug symbols — 175K symbols with complete function names, class layouts, and source file paths. That gave direct access to the engine internals, including the exact implementation of T3IndexBuffer::Decompress (the delta-compressed face index algorithm), BitBufferReadOffset, and the full D3DMesh::TriangleSet serialization logic.

From there:

• Used the V0.5 (Strong Bad/W&G) format from the exsisting script as the starting reference, since V1 is structurally close
• Disassembled the key functions from the iOS binary to get the delta compression algorithm (the main piece that was missing V0/V0.5 use raw indices, V1 introduces bitstream compression)
• Cross-validated by comparing PC compressed indices against iOS raw (uncompressed) indices for the same meshes — got a 70/70 triangle-level match
• Iterated the TriangleSet struct parser against all 358 meshes from EP1 until 356/358 matched the file's declared submesh count exactly

As for coverage — yes, Version 1 should be the only gap in the list, but I tested only on ToMI

[Lilothestitch16]

I see. Btw have you been able to reverse engineer the .ptable, .chore and .anm files from the Telltale Games?