Global Illumination is the ultimate component of your scene that will make it look natural and, therefore, realistic. Unfortunately, achieving the perfect setup for Global Illumination might be tricky. In many cases, the result will not pay for the work that had to be done to achieve the effect.

Understanding GI may sound more complex to understand than it is. In a short description of it, it is a process that involves a lighting source that will directly affect different game objects’ surfaces. The bounce of the light on that surface will cause a soft copy of its color which will bloom on close objects. This light will not have the same strength as the one that came directly from the source, and it will cause the scene not only to be affected by the direct light but also by the bounced light from the objects. That’s the natural behavior in our world. If you want a professional look for your game, you should strive to achieve the best Global Illumination setup in order to go one step further toward achieving perfection.

We’ve been working on a brand new asset called Radiant GI. This asset works for URP and has an easy integration into the final post-processing of your game. You can use Radiant GI in a global volume or a volume that will affect a specific scene area. The second case will give you more control over the behavior of the Global Illumination allowing it to be rendered only in some regions of the scene.

The inspector of Radiant GI was designed specifically to help the user understand its features right away. Divided into five categories, each of them will offer different settings that will guarantee the best result. Radiant GI starts with the General settings section. This category will determine the indirect intensity of the global illumination and other parameters relative to its behavior. The next section is “Quality,” As the name indicates, this category is composed of values that allow users to choose the best balance of quality for their scene in particular. Don’t be afraid to take these values to their higher potential; in the next section, “Performance,” you can adjust Raytracer Accuracy & Downsampling to have the best quality of global illumination while not affecting the performance of your game. Debugging is the last section of Radiant GI, where you can choose whether to see the effect applied on scene view, choose the view mode to clearly understand how global illumination affects that scene in particular, and enable compare mode to get an instant visual comparison.

Radiant GI works with both global and local volumes. This means you can adapt the illumination effect to specific zones on the scene or allow the illumination to render globally.

How to use Radiant GI with Global Volumes

You only need to create a custom global volume and add the Radiant GI component. Every value that you would edit now will affect illumination globally. Usually, applying Radiant GI on a global volume creates a beautiful effect without needing further editing. However, sometimes your scene will require certain zones to be excluded, as the intensity for that zones should be different. That’s why Radiant GI includes a specific option to apply the effect to particular areas on the scene.

How to use Radiant GI with Local Volumes

First, create a local volume that covers the space inside of which you want the illumination to be rendered. Add the Radiant GI component to that local volume and adjust the proper setting until you reach the desired result. Finally, activate the “Limit to Volume Bounds” option. Now the illumination will only affect that zone particularly; see the example bellow…

There’re some ways to add global illumination in real-time. One of the most performant, dynamic and accurate is screen space global illumination. Radiant GI uses this approach for instant global illumination feedback. Global Illumination is challenging though and each technique has some pros and cons. In the case of Radiant GI, since it’s a screen space effect, objects not visible won’t be able to emit light thus when rotating the camera, you can sometimes notice a slight variance in scene illumination.

To compensate this effect, Radiant GI includes 3 fallbacks that can be combined:

1. Reuse Rays. During the raytracing phase, when a ray misses a surface, Radiant GI is capable of reusing successful rays from previous frames.

2. Reflection Probes. Radiant GI can automatically gather the light data stored in the two nearest reflection probes to the camera, making use of blending distance to smooth any transition when camera moves.

3. Reflective Shadow Maps. Finally, Radiant GI can also compute RSM data from the directional light, filling with global illumination coming from objects lit by the main light regardless of their orientation or position.