Fallbacks

intermediate concepts

Radiant GI is a screen-space effect: only objects visible on screen can contribute indirect lighting. The fallback system compensates for this limitation by providing alternative data sources when rays miss.

Note: Radiant GI is 100% GPU-based, requires no pre-computation, and works with dynamic or procedural content. Fallbacks extend its reach without sacrificing these advantages.

Available Fallbacks

Reuse Rays

When a ray misses in the current frame, the system checks whether a ray from a previous frame — emitted from the same screen position — hit a surface. If so, that result is reused.

Cost	Very low
Pros	Smooth GI composition, almost free
Cons	Can introduce ghosting on fast-moving objects. Still limited to surfaces that were recently on screen.
Recommendation	Enable always unless ghosting is problematic. Use a low intensity value.

Reflection Probes

When rays miss, Radiant samples cubemaps from the two nearest reflection probes. This provides approximate off-screen color data.

Cost	Medium
Setup	Add the `Radiant Probe` script to any reflection probe in your scene. Radiant automatically selects the 2 nearest probes to the camera.
Probe modes	Baked (cheapest), Awake (updates once), or Real-time (most accurate but expensive). A real-time probe parented to the camera gives the best results.
Blending	Radiant uses each probe’s importance, intensity, blending distance, and box size to weight the cubemap sampling.
Recommendation	Place at least one probe at the center of each room with Bake mode set to Awake.

Reflective Shadow Maps (RSM)

Renders the scene from the directional light’s point of view, capturing flux, normals, and world positions to compute GI bounces for off-screen geometry.

Cost	High when updating; medium otherwise
Setup	Enable RSM in the Radiant inspector, then add the `Radiant Shadow Map` script to the main directional light.
Update triggers	RSM buffers are recomputed only when the directional light rotates or the camera moves more than 5 meters.
Best for	Outdoor scenes or large open areas where the sun is high, maximizing the RSM capture coverage.

Selection Priority

When multiple fallbacks are enabled, the system selects automatically in this order:

Reflection Probes — used first if available
Reflective Shadow Maps — used if no probes are available
Reuse Rays — used as final fallback

Recommendations

When to use fallbacks: Only enable fallbacks if lighting changes are distracting or affect gameplay. Radiant GI is designed to add subtle indirect lighting, and slight fluctuations when objects enter/leave the frustum are normal for screen-space techniques.

Always enable Reuse Rays — it is nearly free and smooths the result
Interiors: add reflection probes at room centers with Bake mode = Awake
Outdoors: reflective shadow maps work better than probes when the sun is high
Multiple volumes: use different fallback configurations per area for the best balance of quality and performance

Was this page helpful? |