Fenris Creations open-sources CORTAO real-time ambient occlusion technique

Fenris Creations, the studio behind EVE Online and EVE Frontier, has released CORTAO (Circular Occluder Ray-Traced Ambient Occlusion) as open source under the MIT license. This follows their earlier decision to open source the Carbon engine framework. CORTAO is a real-time rendering technique designed to improve ambient occlusion accuracy and stability while maintaining low computational cost, specifically addressing visual artifacts like dark halos and shading flicker during camera movement.

The technique operates without baked scene data, making it suitable for dynamic, player-modified environments such as those in EVE Frontier. Daniel Isheden, Senior Rendering Engineer at Fenris Creations, developed CORTAO and tested it in the demanding conditions of EVE Frontier. The open-source release allows other graphics developers to examine, adapt, and extend the implementation for their own rendering challenges.

How CORTAO handles real-time ambient occlusion

• Circular occluder model: CORTAO uses a circular occluder approach for ray-traced ambient occlusion rather than traditional point or line sampling methods, which contributes to its stability during camera motion.
• Real-time dynamic computation: The technique calculates shading without pre-baked scene data, enabling correct ambient occlusion in environments that change continuously through player construction and modification.
• Artifact reduction: CORTAO specifically targets dark halos and distracting shading shifts that commonly appear around objects as the camera moves, improving visual consistency in complex scenes.
• Performance-constrained design: The implementation was developed within the performance budgets typical of actual games, as emphasized by its creator, rather than as an unconstrained research prototype.
• MIT licensing and Carbon integration: CORTAO is available on GitHub under the MIT license and was developed within and released alongside the open-source Carbon engine framework.

Why it matters

For Linux and open-source game development, CORTAO provides a production-tested ambient occlusion implementation that can be integrated into existing engines without proprietary licensing barriers. The technique's suitability for dynamic, user-generated content environments aligns with growing interest in moddable and persistent-world games on Linux platforms, while its release through the Carbon framework continues Fenris Creations' pattern of contributing usable graphics research back to the broader development community.