Tutorial #3: ILGI
In this tutorial, you'll learn how Immersive Lighting Global Illumination (ILGI) improves the quality of Immersive Lighting and how you can best leverage it in scenes where Immersive Lighting is enabled.
Let's go over a quick primer on what Global Illumination is and how it improves Immersive Lighting
Global Illumination is a technique in computer graphics that models the physics of indirect light (or bounced light). Let's say for example you have an apple sitting on a piece of paper underneath a light. What you'll see is a little bit of red reflected onto the paper underneath the apple depending on how strong the light source is and its angle. That little bit of red reflected back onto the paper is indirect (or bounced) light. It's light that hits the apple and is slightly reflected off of it onto other surrounding surfaces. The light that hits the apple or paper within the line of sight of the light source is direct light.
In the case of Immersive Lighting, imagine your player is walking towards the exit of a cave where it's brightly lit outside. If occlusion detection is enabled, then light rays would not affect the user's lights until they had walked past the exit. With ILGI, you would have indirect light slowly illuminate your lights as you reached the exit as it would in the real world.
Configure ILGI (optional)
In order to use ILGI with Immersive Lighting, we'll need to enable it and set it up for our project. Let's take a look at the settings for Immersive Lighting and review what each does. The settings can be found under Project Settings -> Plugins -> Immersive Lighting.
ILGI Contribution Factor: The contribution factor to apply to each bounce of the Global Illumination
ILGI Ray Trace Tolerance: The tolerance of each ray used to validate the vector of the Directional Light when calculating the Global Illumination
ILGI Ray Trace Variance: How much to vary the rays vertical direction from their initial origin
ILGI Ray Trace Distance: The distance of each trace used to calculate the Global Illumination using the Directional Lights in the scene
ILGI Ray Trace Offset: If a trace collides with an object, this will be how much to back off the impact point by to avoid tracing inside geometry
ILGI Z-Factor: If Consistent Spread is enabled, this will set the static Z-Axis vector component from -1 to 1. 1 = up, -1 = down
ILGI Interpolation Speed: If > 0, this will interpolate ILGI samples at a set speed when sampling lighting for the Immersive Lighting System.
ILGI Max Falloff Distance: The maximum distance used when ILGI Sampling Falloff is enabled and Linear sampling is set as the default.
ILGI Ray Trace Count: The number of traces to used to calculate the Global Illumination using the Directional Lights in the scene
ILGI Bounces: The number of bounces to calculate from the Global Illumination using the Directional Lights in the scene
ILGI Consistent Spread: Whether or not the rays are initially spread evenly when gathering a sample for ILGI.
ILGI Sampling Falloff: Whether or not the bounced samples used are then processed using the specified 'Lighting Influence Method'.
ILGI Optimized Single Location: Whether or not to optimize the Global Illumination using only the origin of the Immersive Lighting system instead of each virtual light source location
Immersive Lighting GI: Whether or not to calculate a form of Global Illumination using only the Directional Lights in the scene if any are available
Evaluate ILGI Settings
If you'd like to test the various settings of ILGI or Surround Lighting, add an Immersive Lighting Sensor to your scene as long as a probe is present and enable ILGI Testing. The sensor is updated either with movement or if one of its properties changes.