Computer Graphics  
Lecture 08 Global Illumination  
Edirlei Soares de Lima  
Global Illumination  
Many surfaces in the real world receive most or all of their  
incident light from other reflective surfaces. This is often  
called indirect lighting or mutual illumination.  
Global Illumination  
Although accounting for the interreflection of light between  
surfaces is straightforward, it is potentially costly because all  
surfaces may reflect any given surface.  
Global Illumination  
Particle tracing process:  
Global Illumination in Games  
Traditionally, video games have been limited to direct lighting.  
The calculations required for indirect lighting were too slow so they  
could only be used in non-realtime situations (such as CG animated  
A solution to this limitation is to calculate indirect light in a  
pre-processing phase (only for static objects and surfaces):  
pre-calculated global illumination.  
Lightmapping is a technique used to store lighting information  
into textures.  
Lightmaps allows global illumination at a relatively low computational  
Instead of lighting the entire scene in  
real time, it pre-calculates all lighting  
information offline, render it into  
textures, and them use the textures  
in real-time.  
Lightmapping in Unity  
To create a lightmap, Unity computes the entire light path  
Lightmapping in Unity  
Test scene:  
Lightmapping in Unity  
Baked Light configuration:  
Static Geometry  
The objects of the scene must be static:  
Lightmapping in Unity  
Real-Time Lightning vs. Lightmapped Scene:  
There is no specular lighting in the lightmapped scene!  
Real-Time Lightning  
Lightmapped Scene  
Lightmapping in Unity  
Lightmapping Settings  
Default resolution  
Higher resolution  
Indirect Light  
With lightmapping we have indirect lighting.  
Real-Time Lightning without Environment Lightning  
Lightmapped Scene without Environment Lightning  
Indirect Light  
With lightmapping we have indirect lighting.  
Real-Time Lightning without Environment Lightning  
Lightmapped Scene without Environment Lightning  
Indirect Light  
With lightmapping we have indirect lighting.  
Real-Time Lightning Emissive Surface  
Lightmapped Scene Emissive Surface  
Light Probes  
Lightmaps only work for static objects. In order to apply the  
baked lighting to dynamic objects we can use light probes.  
A light probe is a point in space that stores information about  
the lighting at that location.  
While lightmaps store information about light hitting the surfaces,  
light probes store information about light passing through a empty  
Placing Light Probes  
Add a new group of light probes:  
GameObject -> Light -> Light Probe Group  
Unlike lightmaps, the resolution of the light probe information  
is entirely defined by how closely packed the probes are  
Usually you begins by involving the area that will contain dynamic  
objects with the probes:  
Placing Light Probes  
Then add more probes depending on how the lighting  
conditions change.  
Place as few light probes as possible. It is essential that you do not  
place them inside static geometry.  
Place then in a more condensed pattern around areas that have  
complex or contrasting light.  
Placing Light Probes  
Even if the gameplay takes place on a 2D plane (for example,  
cars driving around on a road surface), the light probes must  
form a 3D volume.  
Bad choice of light probe positions  
Good choice of light probe positions  
Placing Light Probes  
Light probe positions must take into account that the lighting  
will be interpolated between sets of probes.  
Mixed Lighting  
Lightmaps allow us to compute light offline.  
Limitations: no specular lighting, no real-time shadows, and we need  
light probes to influence dynamic objects.  
Indirect light is the one thing that baked lighting has that real-  
time lighting lacks, because it requires a lightmap.  
Mixed lights allow indirect light to be combine it with real-  
time lighting.  
Of course this means that shading becomes more expensive.  
Mixed Lighting  
To use mixed lighting, the light’s mode  
has to be set to Mixed.  
The lightmap will only store indirect light  
Dynamic objects use the light probes to  
compute indirect light.  
Full Lightmap  
Only indirect light  
Mixed Lighting  
With lightmapping we have indirect lighting.  
Dynamic Object  
Lightmapped Scene  
Mixed Lighting Scene  
Mixed Lighting  
Mixed lighting is as much expensive as real-time lighting (it  
adds lightmaps for indirect light).  
We can improve this by including shadows into lightmaps:  
Shadowmask Mode.  
In this mode, both the indirect lighting and the shadow  
attenuation for mixed lights are stored in lightmaps.  
Mixed Lighting  
Mixed lighting with shadowmask is not as cheap as fully baked  
Subtractive Mode provides the fast and lowest-quality results: it  
renders shadows of dynamic object in real time for only one light, and  
composites them with baked direct and indirect lighting.  
Only recommended for platforms that are unable to use any  
of the other modes.  
No specular lighting;  
Dynamic shadows only for one Directional Light  
Realtime Global Illumination  
Lightmapping works very well for static geometry, but it  
cannot deal with dynamic lights (like the sun traveling across  
the sky).  
To support real-time global illumination, Unity uses  
the Enlighten system (developed by SiliconStudio).  
It still requires a precomputation phase similar to the  
lightmapping process, and it is still limited to static  
It precomputes all possible light bounces in the scene  
and encodes this information for use at runtime.  
Realtime Global Illumination  
Enlighten System:  
Realtime Global Illumination  
Realtime global illumination can be enabled independent of  
baked lighting. In addition, the Light Mode must be set to  
Realtime Global Illumination  
Realtime Global Illumination can also be used for static  
objects that emit light. This makes it possible to vary their  
emission with matching realtime indirect light.  
Realtime Global Illumination  
Precomputed Realtime Global Illumination also has the  
limitation that only static objects can be included in the  
precomputation (moving objects cannot bounce light onto  
other objects).  
However, they can still pick up bounce light from static objects using  
Light Probes.  
Moving ambulance without indirect light  
Moving ambulance with indirect light from light probes  
Exercise 1  
) Add lights and configure global illumination for the morgue  
room scene.  
The scene must have:  
Emissive ceiling lights;  
Indirect lighting;  
Base Scene:  
Further Reading  
Marschner, S., et al. (2015). Fundamentals of Computer  
Graphics (4th ed.). A K Peters/CRC Press. ISBN: 978-  
Chapter 33: Global Illumination