Screen Space Global Illumination
The Screen Space Global Illumination (SSGI) override is a High Definition Render Pipeline (HDRP) feature that uses the depth and color buffer of the screen to calculate diffuse light bounces.
HDRP implements ray-traced global illumination (RTGI) on top of this override. This means that the properties visible in the Inspector change depending on whether or not you enable ray tracing.
SSGI and RTGI completely replace all lightmap and Light Probe data. If you enable this override and the Volume affects the Camera, Light Probes, and the ambient probe, stop contributing to lighting for GameObjects.
Enabling Screen Space Global Illumination
To use this feature in your Scene, you must first enable it for your project and then enable it for your Cameras. To enable features in your project, you use the HDRP Asset and to enable features for your Cameras, you use Frame Settings. You can enable features either for all Cameras, using the Default Frame Settings, or for specific Cameras, by overriding each Camera's individual Frame Settings.
For this feature: The property to enable in your HDRP Asset is: Lighting > Screen Space Global Illumination. The property to enable in your Frame Settings is: Lighting > Screen Space Global Illumination.
Using Screen Space Global Illumination
HDRP uses the Volume framework to calculate SSGI, so to enable and modify SSGI properties, you must add a Screen Space Global Illumination override to a Volume in your Scene. To add Screen Space Global Illumination to a Volume:
- In the Scene or Hierarchy view, select a GameObject that contains a Volume component to view it in the Inspector.
- In the Inspector, navigate to Add Override > Lighting and click Screen Space Global Illumination. HDRP now calculates SSGI for any Camera this Volume affects.
API
To access and control this override at runtime, use the Volume scripting API. Because of how the Volume system works, you edit properties in a different way to standard Unity components. There are also other nuances to be aware of too, such as each property has an overrideState. This indicates to the Volume system whether to use the property value you set, or use the default value stored in the Volume Profile. For information on how to use the API correctly, see Volume scripting API.
Properties
To edit properties in any Volume component override, enable the checkbox to the left of the property. This also tells HDRP to use the property value you specify for the Volume component rather than the default value. If you disable the checkbox, HDRP ignores the property you set and uses the Volume’s default value for that property instead.
The properties visible in the Inspector change depending on whether or not you enable ray tracing for this effect:
To not use ray tracing and instead use the screen-space global illumination solution, disable Ray Tracing in the Inspector and see Screen-space for the list of properties.
To use ray tracing, enable Ray Tracing in the Inspector and see Ray-traced for the list of properties.
Screen-space
| Property | Description |
|---|---|
| Enable | Indicates whether HDRP processes SSGI for Cameras in the influence of this effect's Volume. |
| Ray Tracing | Indicates whether HDRP uses ray tracing to calculate global illumination. If you enable this property, it completely changes the implementation for this Volume override and exposes a new set of properties to control the ray-traced global illumination. For information on ray-traced global illumination, see ray-traced global illumination. For information on the properties that control the ray-traced global illumination, see the Ray-traced properties section below. |
| Quality | Specifies the overall quality of the effect. The higher the quality, the more resource-intensive the effect is to process. |
| Full Resolution | Toggles whether HDRP calculates SSGI at full resolution. |
| Ray Steps | The number of ray steps to use to calculate SSGI. If you set this to a higher value, the quality of the effect improves, however it is more resource intensive to process. |
| Filter Radius | The size of the filter use to smooth the effect after raymarching. Higher value mean blurrier result and is more resource intensive. |
| Depth Tolerance | Use the slider to control the tolerance when comparing the depth of the GameObjects on screen and the depth buffer. Because the SSR algorithm can not distinguish thin GameObjects from thick ones, this property helps trace rays behind GameObjects. The algorithm applies this property to every GameObject uniformly. |
Ray-traced
| Property | Description |
|---|---|
| Ray Tracing | Enable this to make HDRP use ray tracing to evaluate indirect diffuse lighting. This makes extra properties available that you can use to adjust the quality of Ray-Traced Global Illumination. |
| LayerMask | Defines the layers that HDRP processes this ray-traced effect for. |
| Mode | Defines if HDRP should evaluate the effect in Performance or Quality mode. This property only appears if you select set Supported Ray Tracing Mode in your HDRP Asset to Both. |
| Quality | Specifies the preset HDRP uses to populate the values of the following nested properties. The options are: • Low: A preset that emphasizes performance over quality. • Medium: A preset that balances performance and quality. • High: A preset that emphasizes quality over performance. • Custom: Allows you to override each property individually. This property only appears if you set Mode to Performance. |
| Max Ray Length | Controls the maximal length of rays. The higher this value is, the more resource-intensive ray traced global illumination is. |
| Clamp Value | Set a value to control the threshold that HDRP uses to clamp the pre-exposed value. This reduces the range of values and makes the global illumination more stable to denoise, but reduces quality. |
| Full Resolution | Enable this feature to increase the ray budget to one ray per pixel, per frame. Disable this feature to decrease the ray budget to one ray per four pixels, per frame. This property only appears if you set Mode to Performance. |
| Upscale Radius | Controls the radius of the up-scaler that HDRP uses to build the GI. The larger the radius, the more neighbors HDRP uses to build the GI, the better the quality. This property only appears if you set Mode to Performance. |
| Sample Count | Controls the number of rays per pixel per frame. Increasing this value increases execution time linearly. This property only appears if you set Mode to Quality. |
| Bounce Count | Controls the number of bounces that global illumination rays can do. Increasing this value increases execution time exponentially. This property only appears if you set Mode to Quality. |
| Denoise | Enable this to enable the spatio-temporal filter that HDRP uses to remove noise from the Ray-Traced global illumination. |
| - Half Resolution Denoiser | Enable this feature to evaluate the spatio-temporal filter in half resolution. This decreases the resource intensity of denoising but reduces quality. |
| - Denoiser Radius | Set the radius of the spatio-temporal filter. |
| - Second Denoiser Pass | Enable this feature to process a second denoiser pass. This helps to remove noise from the effect. |
Limitations
Ray-traced global illumination
Currently, ray tracing in HDRP does not support decals. This means that ray-traced global illumination does not affect decals in your Scene. When rendering Reflection Probes screen space global illumination is not supported.