EVE Frontier test bed yields CORTAO, an open-source ambient occlusion technique from Fenris Creations

In Brief:

• On Nov. 12, 2026, Fenris Creations released CORTAO (Circular Occluder Ray-Traced Ambient Occlusion), a rendering technique it has made open source.
• Senior Rendering Engineer Daniel Isheden built it. Developers can get it through the Carbon engine or from a standalone GitHub repository under the MIT license.
• The studio optimized and tested CORTAO in EVE Frontier (official site). Shading is calculated in real time with no baked scene data, so it suits worlds that players build and reshape.

CORTAO, a new ambient occlusion technique from Fenris Creations, is now open source. The studio says it gives more accurate and stable shading while keeping rendering cost low. Developers can get it today through Carbon, the engine framework Fenris open-sourced earlier this year.

The release was announced on X by the EVE Frontier account. A post from @EVE_Frontier read: “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.”

The same post went on: “Developed through Carbon. Tested in EVE Frontier.”

Shading for worlds players reshape

CORTAO works out shading in real time and has no need for baked scene data. According to Fenris, that suits EVE Frontier, a game where players are always building and reworking structures.

The studio said the technique reduces the dark halos and unstable shading that can appear around objects. Isheden, a senior rendering engineer at Fenris, said the issue stands out once things start moving.

“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 its implementation in EVE Frontier, the studio’s space survival MMO, which is still in development. Tests ran across varied environments, from open space to closed-in interiors.

Under the hood

CORTAO is a fresh approach to screen-space ambient occlusion. It takes data from the current view, treats nearby surfaces as circular occluders, and then works out how much ambient light those occluders block.

First, the technique samples depth information close to each pixel and discards any samples outside the potential occlusion volume. The samples that remain are turned into circular proxy occluders that approximate the 3D space around the pixel. A precomputed lookup table determines where rays strike those proxies, and the fraction of rays that pass through decides how much ambient light the pixel gets.

Each pixel can cast as many as 32 rays. Isheden said getting it to run fast enough for real time was the hardest part.

Fenris built CORTAO as a drop-in replacement for an engine’s existing screen-space ambient occlusion stage, so developers are not tied to Carbon to use it.

How it compares with GTAO

Fenris measured CORTAO against Ground Truth Ambient Occlusion (GTAO), a horizon-based SSAO technique. Using a recreated San Miguel cafe scene, the company said four-sample CORTAO scored a lower mean squared error against a ray-traced reference than any GTAO configuration it tried.

CORTAO also kept occlusion more consistent as sample counts changed, the studio said. Fenris reported that it was more conservative around depth discontinuities and showed fewer heavy halos and view-dependent artifacts.

From side project to release

The technique started as independent research by Isheden. Fenris then gave him a production environment where he could test and refine it at scale.

“CORTAO was honestly born out of spite,” Isheden said. He began the work after hitting problems with GTAO, particularly on vegetation, something EVE Online has little of.

Ben Hunter, director of core technology at Fenris Creations, linked the project to how the studio handles research.

“Good rendering research needs room to develop, and a game that puts it under pressure,” Hunter said.

Where to get it

CORTAO’s code is released under the MIT license. On GitHub, Fenris has published a standalone repository alongside a version optimized for Carbon. The EVE Frontier website hosts documentation and visual comparisons, and the studio has uploaded a YouTube video called “CORTAO in EVE Frontier.”

Hunter said making the technique open source lets “other teams can examine the decisions behind it and adapt it to challenges we haven’t encountered ourselves.”