Introduction to Precomputed Realtime GI

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In Unity, there are two distinct techniques available for precomputing global illumination (GI), or bounced lighting. These are Baked GI and Precomputed Realtime GI. This tutorial focuses on Precomputed Realtime GI.

When working with Precomputed Realtime GI, a lighting precompute is the process of calculating the bounce of light around the static geometry within a Scene in the Unity Editor and storing this data for use at run time. This process reduces the number of lighting calculations that must be performed at run time, allowing realtime bounced lighting while maintaining interactive framerates.

When using Baked GI, traditional lightmap textures are generated offline during the precompute process. These textures then exist as assets within the project and cannot be changed at run time. Precomputed Realtime GI does not create lightmap assets in the same way. Instead, lighting data is saved as a Lighting Data Asset which contains the information needed to generate and update a set of low resolution lightmaps interactively, at run time.

Unless our Scene has been properly prepared and optimized, the time it takes to complete these calculations can become excessive. In this tutorial, we will learn how to optimize a Scene for Enlighten (the backend for Unity’s Precomputed Realtime GI and Baked GI solutions) so that lighting precomputes take minutes rather than hours.

Over the course of the document we will cover:

  • How to determine an appropriate lighting resolution for our Scenes.

  • What Charts are and how they affect our precompute times.

  • How to start the precompute process.

  • Using probe lighting to reduce the complexity of our lighting solution.

  • Improving auto-unwrapped UVs generated by Unity’s Precomputed Realtime GI.

  • What Clusters are and how they are used to generate globally illuminated lighting.

  • Using Lightmap Parameters to fine-tune our lighting on a per-object basis.

Once we have learned and applied these techniques, we can leverage the benefits of using Precomputed Realtime GI: fast lighting iteration times, the ability to experiment more rapidly during the lighting process and realtime bounced lighting during gameplay.

Reducing precompute times from hours to minutes

In the Lighting Tutorial Scene used for this tutorial, precomputing the lighting with a default, non-optimized setup took around 7.5 hours on our test machine. For a Scene of this complexity, clearly this is unacceptable.


Default Scene: Precompute took 7.5 hours. Optimized Scene: Precompute took 2.25 minutes.

Following around 30 minutes of Scene preparation using the techniques covered in this tutorial, the precompute time was 2.25 minutes for a production-quality result. Considering that we can rapidly iterate on Scene lighting without needing to re-calculate GI and change GI lighting during gameplay, the attractive benefits of this technology are quickly apparent.

Downloading assets for this tutorial

Throughout this tutorial we will be referring to the Lighting Optimisation Tutorial project available from the Unity Asset Store.

In this written tutorial, we will be using the example Scenes contained within the Scenes/Article folder: LightingTutorialOptimal, LightingTutorialNonOptimal and LightingTutorialStart.

  • LightingTutorialOptimal has been set up according to this tutorial and is intended to represent an example of how production-ready lighting results can be achieved with minimal precompute time using Unity’s Precomputed Realtime GI.

  • LightingTutorialNonOptimal reflects a lot of the common problems we see in projects that either don’t finish baking, or take an unacceptably long time. This is a good reference for how Scenes should not be configured.

  • LightingTutorialStart will be the Scene which we are working with throughout this tutorial. As we follow the steps laid out in this tutorial, we will take this Scene to a completed, production-ready result.


  1. Introduction to Lighting and Rendering
  2. Choosing a Lighting Technique
  3. The Precompute Process
  4. Choosing a Rendering Path
  5. Choosing a Color Space
  6. High Dynamic Range (HDR)
  7. Reflections
  8. Ambient Lighting
  9. Light Types
  10. Emissive Materials
  11. Light Probes
  1. Introduction to Precomputed Realtime GI
  2. Realtime Resolution
  3. Understanding Charts
  4. Starting the precompute process
  5. Probe lighting
  6. Unwrapping and Chart reduction
  7. Optimizing Unity's auto unwrapping
  8. Understanding Clusters
  9. Fine tuning with Lightmap Parameters
  10. Summary - Precomputed Realtime GI
  1. Lighting Overview
  2. Lights
  3. Materials
  4. The Standard Shader
  5. Textures
  6. Using Skyboxes
  7. A Gentle Introduction to Shaders
  8. Using detail textures for extra realism close-up
  9. Frame Debugger
  1. Cameras
  2. Image Effects: Overview
  1. Meshes
  2. Mesh Renderers and Mesh Filters
  1. Where to Start?
  2. Preparing Unity Render Settings
  3. Lighting Strategy
  4. Modeling
  5. Standard Shader/Material PBS and texturing
  6. Lighting and Setup
  7. Understanding Post Process Features
  8. Dynamically Lit Objects
  9. Sample Project File
  1. Using Cameras
  2. Using Lights
  3. Fun with Lasers!
  4. The Particle System
  5. Cinematic Explosions - PIT
  6. Cinematic Composition - PIT
  7. Image Effects: Overview
  8. Fun with Explosions!
  9. Exploring the Blacksmith Environment
  1. Turning it up to 11: Making Unity 5 look Awesome!
  1. Substance - Introduction
  2. Substance - Understanding PBR
  3. Substance - Working with PBR in Unity
  4. Substance - Using Substance materials in Unity
  5. Substance - Optimization for Substance materials
  6. Substance - Creating rock shapes
  7. Substance - Creating rock material, Pt 1
  8. Substance - Creating rock material, Pt 2
  9. Substance - Creating the dirt ground material
  10. Substance - Creating the rock ground material, Pt 1
  11. Substance - Creating the rock ground material, Pt 2
  12. Substance - Publishing the Substance
  13. Substance - Creating a blocking scene
  14. Substance - Creating the ground model
  15. Substance - Modelling the rock assets
  16. Substance - Texturing the upper body
  17. Substance - Exporting textures from Substance Painter
  18. Substance - Creating a scene in Unity, Pt 1
  19. Substance - Creating a scene in Unity, Pt 2
  1. Introduction and Goals
  2. Flame Particles Overview
  3. Particle Emission and Color
  4. Adding Movement To Particles With Noise
  5. Creating The Ember Particles
  6. Adding Lighting To Particles
  7. Creating Sparks With Particle Trails
  8. Particle Question and Answers
  1. Introduction and Goals
  2. Adding a Second Camera
  3. Adding Minimap Icons
  4. Render Textures and UI
  5. Adding A UI Mask and Border Image
  6. Questions and Answers
  1. Session Introduction
  2. Rendering In Unity
  3. Anatomy Of An Unlit Shader
  4. The Vertex Function
  5. The Fragment Function and Color Tint
  6. Making A Transparent Shader
  7. Displacing Vertices and Clipping Pixels
  8. Questions and Answers
  1. Introduction and Session Goals
  2. The VideoPlayer Component
  3. Texturing Objects With Video
  4. Playing and Pausing
  5. Playing A New Clip
  6. Displaying Current Time and Clip
  7. Animated Playhead
  8. Questions and Answers
  1. Overview and Goals
  2. Tonemapping and Color Grading
  3. Camera Movement & Animation
  4. Post Processing Volumes
  5. Timeline & Cinemachine
  6. Questions and Answers