Open Game Engine Exchange

The Open Game Engine Exchange (OpenGEX) format is a text-based file format designed to facilitate the transfer of complex scene data between applications such as modeling tools and game engines. It is intended to be a graphics and animation pipeline format used during the game development process.

The OpenGEX format is built upon the data structure concepts defined by the Open Data Description Language (OpenDDL), a generic language for the storage of arbitrary data in human-readable format.

The OpenGEX format was created because Collada, the open standard that we all hoped would provide a well-supported asset exchange format, has proven to be an unreliable mess. The most common source of problems has been the poor quality of the Collada export plugins available for software such as 3D Studio Max and Maya, and we attribute this to Collada’s over-engineered design and its mutating under-specified format.

Compare OpenGEX, Collada, and glTF

OpenGEX Specification

The official specification for OpenGEX version 3.0 is available at the following location.
It is also available in print on Amazon.

Download OpenGEX Specification
(Last updated 8-Mar-2022)

OpenGEX Export Plugins and Import Template

Export plugins for 3ds Max and Maya are available on GitHub at the following location.

OpenGEX Reference Code

These exporters support the following features:

• Hierarchical scene organization (node trees).
• Factored node transforms where necessary (e.g., splitting into position, rotation, and scale).
• Object instancing (multiple nodes can reference the same object).
• Geometry objects, light objects, and camera objects.
• Multiple materials per mesh with independent binding per instance.
• Multiple vertex colors and texture coordinate sets per mesh.
• Skinned meshes (skeleton, bind-pose transforms, bone influence weighting data).
• Morphed meshes (also known as blend shapes or shape keys).
• Keyframe animation for all node transforms and morph weights.
• Linear, Bézier, and TCB animation curves.
• Material colors and textures (diffuse, specular, normal, emission, opacity, transparency).
• Texture coordinate transforms.

The GitHub repository also contains a reference importer. This is a template derived from the OpenGEX import plugin for the C4 Engine, with the engine-specific parts stripped out. It reads an OpenGEX file, validates it, and creates all of the structures necessary to construct a scene, but application-specific processing must be added in the appropriate places to support any other software.

About

OpenGEX was created in 2013 by Eric Lengyel and is implemented in the art pipeline of the C4 Engine.

The OpenGEX file format is registered with the Internet Assigned Numbers Authority (IANA) as the model/vnd.opengex media type.