George Tsagkarakis
In Brief:
- Fenris Creations released CORTAO (Circular Occluder Ray-Traced Ambient Occlusion), an open-source rendering technique, on Nov. 12, 2026.
- Senior Rendering Engineer Daniel Isheden created it. It’s available through the Carbon engine and in a standalone GitHub repository under the MIT license.
- The studio optimized and tested the technique in EVE Frontier (official site). It calculates shading in real time without baked scene data, which suits worlds that players build and reshape.
Fenris Creations has released CORTAO, an open-source ambient occlusion technique that the studio says produces more accurate and stable shading at low rendering cost. It’s available now through Carbon, the engine framework Fenris open-sourced earlier this year.
The EVE Frontier account announced the release on X. “Introducing CORTAO,” a post from @EVE_Frontier read. “Created by Daniel Isheden at Fenris Creations, CORTAO is a new open-source rendering technique delivering more accurate, stable ambient occlusion at low rendering cost.”
Introducing CORTAO.
Created by Daniel Isheden at Fenris Creations, CORTAO is a new open-source rendering technique delivering more accurate, stable ambient occlusion at low rendering cost.
Developed through Carbon. Tested in EVE Frontier.
evefrontier.com/en/news/cortao…
The post added: “Developed through Carbon. Tested in EVE Frontier.”
Built for worlds that change
CORTAO calculates shading in real time and doesn’t need baked scene data. Fenris said that makes it a fit for EVE Frontier, where players keep building and reshaping structures.
The studio said the technique cuts down the dark halos and shifting shading that can show up around objects. Isheden, a senior rendering engineer at Fenris, said that problem is easy to spot in motion.
“Small errors in shading can make an otherwise convincing scene feel wrong, especially when they become visible as the camera moves,” Isheden said.
Fenris optimized and tested the implementation in EVE Frontier, its space survival MMO that is still in development. The testing covered a range of settings, from open space to enclosed interiors.
How it works
CORTAO is a new take on screen-space ambient occlusion. It uses information from the current view to represent nearby surfaces as circular occluders, then calculates how much ambient light they block.
The technique samples nearby depth information and throws out samples that fall outside the potential occlusion volume. The remaining samples become circular proxy occluders that approximate the 3D area around a pixel. A precomputed lookup table finds where rays hit those proxies, and the share of rays that get through sets the ambient light level.
It casts up to 32 rays per pixel. Isheden said the main challenge was making it fast enough to run in real time.
Fenris designed CORTAO to replace an engine’s existing screen-space ambient occlusion stage. That means developers can use it outside Carbon.
Benchmarks against GTAO
Fenris compared CORTAO with Ground Truth Ambient Occlusion (GTAO), a horizon-based SSAO technique. In a recreated San Miguel cafe scene, the company said four-sample CORTAO had a lower mean squared error against a ray-traced reference than every GTAO configuration it tested.
The studio said CORTAO also held a more consistent level of occlusion across sample counts. It was more conservative around depth discontinuities and produced fewer heavy halos and view-dependent artifacts, according to Fenris.
Started as side research
CORTAO began as Isheden’s independent research. Fenris gave him a production environment to test and refine it at scale.
“CORTAO was honestly born out of spite,” Isheden said. He started the work after running into problems with GTAO, especially on vegetation, which EVE Online has little of.
Ben Hunter, director of core technology at Fenris Creations, tied the project to the studio’s approach to research.
“Good rendering research needs room to develop, and a game that puts it under pressure,” Hunter said.
Release details
The code is under the MIT license. Fenris published both a standalone repository and a Carbon-optimized version on GitHub. Documentation and visual comparisons are on the EVE Frontier website, and the studio posted a video titled “CORTAO in EVE Frontier” on YouTube.
Hunter said open-sourcing the technique means “other teams can examine the decisions behind it and adapt it to challenges we haven’t encountered ourselves.”
