.CSO

Introduction

A .cso file is a compiled shader object: an HLSL shader compiled ahead of time for Microsoft’s Direct3D. Visual Studio writes one per shader when it builds a project, and a program reads the file and passes its bytes to Direct3D, which hands them to the graphics driver to turn into code for the particular GPU.

Shaders for shader model 5 and earlier, compiled with fxc, hold DXBC bytecode. Shader model 6 shaders, compiled with dxc, hold DXIL, a form of LLVM bitcode. Both use the same container.

Structure

The file starts with the four characters DXBC, a 16-byte checksum of the rest of the file, a version number, the total size and the number of chunks, followed by a table of offsets to each chunk. Every chunk has a four-character name and a size. Typical chunks are RDEF (resources the shader uses), ISGN and OSGN (input and output signatures), SHDR or SHEX (DXBC bytecode), DXIL (DXIL bytecode) and STAT (statistics). All numbers are little-endian.

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