Light Propagation Volumes GI

From Epic Wiki 


Light Propagation Volumes (LPV) are currently implemented as a Work in Progress feature! Expect bugs and flaws while working with them!


Description

Light propagation volumes is a technique to approximately achieve global illumination (GI) in Real-time.
It uses lattices and spherical harmonics (SH) to represent the spatial and angular distribution of light in the scene.


How to enable it

The use of Light propagation volumes is disabled by default, since this feature is still under development by Epic.
To enable this feature you need to edit the "ConsoleVariables.ini" file, which is located in your engine config folder. The default location for it is as follows

C:\Program Files\Unreal Engine\4.0\Engine\Config\

Now you have to add r.LightPropagationVolume=1 at the bottom, right below the [Startup] category.
Now your file should look like this: 

; ConsoleVariables.ini
;
; This file allows to set console variables on engine startup (In undefined order).
; Console variables also can be set in engine ini files (e.g. BaseEngine.ini, DefaultEngine.ini) in the [SystemSettings] section.
; This file should be in the source control database (for the comments and to know where to find it)
; but kept empty from variables.
; A developer can change it locally to save time not having to type repetitive
; console variable settings. The variables need to be in the section called [Startup].
; Later on we might have multiple named sections referenced by the section name.
; This would allow platform specific or level specific overrides.
; The name comparison is not case sensitive and if the variable doesn't exists it's silently ignored.
;
; Example file content:
;
; [Startup]
; FogDensity = 0.9
; ImageGrain = 0.5
; FreezeAtPosition = 2819.5520 416.2633 75.1500 65378 -25879 0

[Startup]

; Uncomment to get detailed logs on shader compiles and the opportunity to retry on errors
;r.ShaderDevelopmentMode=1
r.LightPropagationVolume=1

Now you have to start/restart your Editor.

But before you can actually use this feature you need to change some settings inside the Editor.

DirLight.png
First of all you have to place a " Directional Light " in your scene.

By either clicking with your right mouse button in the viewport and selecting " Place Actor - Directional Light " or by dragging it from the left " Modes " tab into your scene.

As next you need to go into the properties of your newly created Light. You now need to check the " Affect Dynamic Indirect Lighting " option in order to activate the use of LPV.
In case you don't see this option, make sure that the " Show All Advanced Details " option is checked inside the Details panel. You can find this option under the little Eye icon Eye-ico.gif right next to the search bar.
As next scroll down to the " Cascaded Shadow Maps " category and increase the value of " Dynamic Shadow Distance StationaryLight " (Dynamic Shadow Distance Movable if it is a Movable light) to 10.000.

Now you have to disable the use of Lightmass, by going into your World Settings. WorldSet.gif
In here you have to look for an option called " Force No Precomputed Lighting " which is located under the Lightmass category, check the checkbox to disable the use of Lightmass. Now you can close the World Settings tab or window.

Once this is done you actually need to re/build your lighting to invalidate and delete all previous existing baked data.

Congratulations, now you have global illumination in real-time.

Tweaking

No matter that this feature is actually under development, there are already some option for you to tweak.
To get these options you have to place a " PostProcessVolume " in your scene. Once again simple drag & drop a " PostProcessVolume " from the " Volumes " list under the "Modes" tab into your scene.

Now in its properties scroll all the way down to the " PostProcessVolume " category and check the " Unbound " checkbox. This will make sure that your PP is used in the whole level and not just inside its boundaries.
Now scroll up until you see the "Light Propagation Volume" category and expand it.

Property Description
Intensity How strong the dynamic GI from the LPV should be. 0 is off, 1.0 is normal value and anything above it can be used to boost the effect.
(DISABLED) Grid Warp Intensity The strength of the warp offset for reducing light bleeding. 0 is off, 1.0 is normal value and anything above it can be used to boost the effect.
Light Injection Bias Bias applied to the light injected into the LPV in cell units ( not Unreal Units ). Increase this value to reduce bleeding through thin walls.
Size The size of the LPV volume, in Unreal Units.
Secondary Occlusion Intensity Secondary occlusion strength (bounce light shadows). Set to 0 to disable.
Geometry Volume Bias Bias applied to the geometry volume in cell units ( not Unreal Units ). Increase to reduce darkening due to secondary occlusion.
Emissive Injection Intensity No information is given at this time. But i guess it controls the injection of emissive materials.
Transmission Intensity How strong the light transmission from the LPV should be. 0 is off, 1.0 is normal value and anything above it can be used to boost the effect.


Thats it, folks! You probably have to play around with these settings a bit to get proper results out of it.
But it's a start.

Helpful things to get you started

  • This ZIP File contains the Cornell Box as a Map for the UE4. So that you can tweak the settings more easy.


References