.X

Introduction

The X format is Microsoft’s model format for Direct3D, introduced with DirectX in the 1990s. The D3DX helper library in the DirectX SDK could load an X file straight into a mesh, so it was widely used in Windows games and samples of the DirectX 8 and 9 era. A file can hold meshes with normals, texture coordinates and materials, a hierarchy of frames, skin weights and animation.

Microsoft has since retired D3DX and the format with it, and newer engines use FBX or glTF instead. X files still turn up in older games and teaching material.

Structure

Every X file starts with a 16-byte header: the magic xof , a version such as 0302 or 0303, a format, and the size of floats, 0032 or 0064. The format is txt for text, bin for binary, or tzip and bzip for compressed text and binary.

The body is a list of data objects, each an instance of a template. Templates are declared types such as Frame, FrameTransformMatrix, Mesh, MeshNormals, MeshTextureCoords, MeshMaterialList, Material and AnimationSet. Objects nest, so a frame holds its transform, its meshes and its child frames.

xof 0303txt 0032
Mesh Triangle {
  3;
  0.0; 0.0; 0.0;,
  1.0; 0.0; 0.0;,
  0.0; 1.0; 0.0;;
  1;
  3; 0, 1, 2;;
}

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