Computer Graphics - Global Illumination

Computer Graphics

Lecture 08 – Global Illumination

Edirlei Soares de Lima

<edirlei.lima@universidadeeuropeia.pt>

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

films).

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!

Lightmapping

•

Lightmapping is a technique used to store lighting information

into textures.

–

Lightmaps allows global illumination at a relatively low computational

cost.

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

offline:

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

space.

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

positioned.

–

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

information.

–

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

lighting.

–

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.

Limitations:

–

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

objects.

•

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.

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

1

) Add lights and configure global illumination for the morgue

room scene.

–

The scene must have:

•

Emissive ceiling lights;

Indirect lighting;

Shadows;

•

https://assetstore.unity.com/packages/3d/environments/morgue-room-pbr-65817

–

Base Scene: http://www.inf.puc-rio.br/~elima/cg/morgue_room.html