MDX Format (Vertex Data)

The .mdx format is a companion file that always pairs tightly with a .mdl model. While the .mdl file handles the complex math, skeletal hierarchy, and animation logic, the .mdx file acts as bulk storage; holding the massive lists of raw 3D coordinates (vertices) that make up the physical shape of the model.

Architecturally, the swkotor.exe engine treats these two files as a single combined asset: the .mdl dictates where and how the model moves, and the .mdx provides the points to physically draw on the screen.

At a Glance

Property	Value
Extension(s)	`.mdx`
Magic Signature	Raw binary stream (No explicit signature block)
Type	Interleaved Vertex Payload Array
Rust Reference	View `rakata_formats::Mdx` in Rustdocs

Data Model Structure

Rakata safely consumes the unindexed byte sequences into a typed geometry definition mapped within rakata_formats::Mdx.

At the raw binary level, .mdx data is strictly an interleaved buffer. Variables (like positional 3D XYZ vectors, Texture Parameter UV planes, and light-calculating Normals) are sequentially woven directly across the byte stream.

Engine Audits & Decompilation

Deep Dive: For an exhaustive archive of the Ghidra decompilation notes detailing the exact byte-level layout of the binary MDL/MDX format and engine loading pipeline, refer to the MDL & MDX Deep Dive.

The following documents the engine’s exact load sequence and structure for .mdx interleaved data pipelines mapped from swkotor.exe.

(Decompilation logic for this section was entirely audited and verified via native Ghidra pipeline against swkotor.exe, explicitly pulling from InputBinary::Read (0x004a1230) and InputBinary::ResetMdlNode (0x004a0900).)

Loading and Lifecycle

Pipeline Event	Ghidra Provenance & Engine Behavior
Memory Wrapping	Triggered immediately alongside the `.mdl`. The wrapper dynamically outlines the exact byte-count of `.mdx` data required (`wrapper + 0x08`).
Buffer Liberation	MDX arrays are entirely stateless. Once `InputBinary::ResetMdlNode` computes the geometry arrays and translates the buffer directly into the OpenGL hardware render-pools during loading, the engine immediately calls `free()` wiping the MDX byte arrays from physical memory entirely.

TriMesh Structural Addressing

The KOTOR Engine avoids parsing the MDX data by scanning through it block-for-block. Instead, traversing the actual MDL hierarchy drives vertex payload requests explicitly.

Mapped Property	Ghidra Provenance & Engine Behavior
Array Slicing	Every distinct `TriMesh` instantiated in the parent MDL tree explicitly registers an `mdx_data_offset` pointer (`TriMesh + 0x144`). This dictates exactly where the engine explicitly seeks within the interleaved `.mdx` payload array to fetch this mesh’s native points.
Node Alignment Constraints	Vanilla assets maintain extremely strict alignment formats. Meshes are dynamically sorted prior to hardware parsing: static rendering models fall to the top of the index chain, whereas dynamic procedural meshes (like character `.Skin` nodes) are specifically dumped sequentially to the rear of the `.mdx`.

Note

Ghost Payload Sentinels During memory extraction, the engine implicitly pads geometric mesh payloads out to distinct 16-byte aligned boundaries using Terminator Rows. Any mesh vertex iteration falling slightly out of stride will be explicitly back-filled with ghost/sentinel float arrays ([0.0, 0.0, 0.0]) to ensure OpenGL buffer calculations remain strictly uniform without overflowing pointer indexes during hardware streaming.

Proposed Linter Rules (Rakata-Lint)

Incorrectly calculated .mdx offset spans or payload array lengths can cause the engine to read misaligned bytes or overflow data bounds. Providing a linter rule to validate these payload alignments helps prevent geometry corruption and potential engine/gpu crashes.

While rakata-lint currently only evaluates GFF formats and does not yet parse .mdx buffers dynamically, the engine behaviors above hint at the foundational requirements for .mdx stability:

Planned Lint Diagnostics:

Mesh Slice Verification: Enforces explicit iteration seeking. Validates .mdx vector boundaries by explicitly jumping pointers down the file according to individual mdx_data_offset assignments mapped on explicitly bound TriMesh headers, rather than assuming unverified sequential payload lengths.

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