GTAO
GTAO, or Ground Truth Ambient Occlusion, estimates how much nearby geometry blocks ambient illumination at each visible surface. It reads the camera's depth and surface information, searching the surrounding screen-space neighborhood for occluders. The result adds contact definition in corners, creases, and the spaces between close objects.
Because it works in screen space, it only knows about geometry represented in the current view. It is not a full-scene visibility solution and cannot replace baked indirect lighting or directional shadows. Large radii can expose missing off-screen information; excessive contrast can make surfaces look dirty rather than better grounded.
The controls in Features > GTAO balance sampling quality, spatial reach, contrast, and temporal stability. Start by choosing the physical size of the detail you want to emphasize, then adjust quality and filtering to resolve it.
Settings are saved with the level and update live. None of these controls requires a lighting rebake.
Spectral GTAO runs on the desktop SM5-or-higher deferred, non-stereo path. It is not the mobile, forward, or stereo AO solution. Native screen-space AO is suppressed when the Spectral path actually runs.
Core
Enabled
Default: enabled.
Turns Spectral GTAO on or off for a supported view. Disable it to separate AO darkening from baked lighting and shadows. An enabled checkbox does not make an unsupported render path run GTAO.
Quality
Default: Medium.
Controls how many directions and steps the AO search samples. More samples improve coverage at greater GPU cost.
| Choice | Slices | Steps |
|---|---|---|
| Low | 2 | 2 |
| Medium | 5 | 3 |
| High | 9 | 3 |
| Ultra | 12 | 3 |
A slice is a search direction through the view-space neighborhood. Quality does not change the world-space search radius or the render resolution.
Resolution Divisor
Default: 2. Range: 1 to 8.
Divides the AO render dimensions. 1 is full resolution, 2 is half resolution, and 4 is quarter resolution. Larger values reduce cost but lose fine details and can make small contacts less stable.
This is the opposite of a quality multiplier: a larger divisor means fewer AO pixels.
Occlusion
Radius
Default: 60 cm. Range: 1 to 500 cm.
World-space reach of the occlusion search. A small radius emphasizes close contact. A larger radius includes broader nearby forms and can darken larger areas.
Radius is not shadow darkness. Increasing it to make AO stronger also changes which geometry participates.
Shadow Power
Default: 2.2. Range: 0.1 to 4.
Contrast curve applied to the final AO. Higher values make contact darkening stronger. It changes the appearance of the result without extending the search.
If the scene looks dirty or overly outlined, reduce this before shrinking the search radius purely to reduce darkness.
Stability
Denoise Passes
Default: 2. Range: 0 to 4.
Number of edge-preserving smoothing passes. 0 disables this filtering. More passes reduce noise at additional cost, but excessive smoothing can make fine AO less distinct.
Temporal Stability
Default: enabled.
Accumulates information from previous frames to reduce noise. Evaluate it with moving objects and a moving camera, not only a still screenshot.
Temporal History Weight
Default: 0.82. Range: 0 to 0.95. Available when Temporal Stability is enabled.
Controls how much previous frames contribute. Higher values produce a steadier image but respond more slowly when the scene changes. Lower values respond sooner but expose more current-frame noise.
If AO trails a moving object, reduce history weight before adding more spatial denoise passes.
Advanced
Falloff Range
Default: 0.615. Range: 0.05 to 1.
Fraction of Radius over which distant occlusion fades away. Higher values spread the fade over more of the search radius; lower values concentrate it near the outer limit.
It changes the fade inside the existing search, not its maximum reach.
Thin-Occluder Compensation
Default: 0. Range: 0 to 1.
Reduces excessive darkening caused by thin objects. At 0 the compensation is off. Increase it when narrow geometry contributes too much AO, while checking that genuine contacts still remain visible.
Material exception
The GTAO Disable material node, in the Spectral material-node category, excludes the material's visible pixels from Spectral GTAO. Drop it into the graph without connecting a wire. It has no input to tune. Use the node where the material should not receive this AO rather than weakening the effect for the entire level.
Overrides
The saved level values are applied at game-setting priority. A higher-priority console or device-profile override can still win. If the displayed value seems ineffective, check the render path and active overrides before rebaking.
For an evaluation checklist, see Tuning GTAO.