Light, Shadows, and Global Illumination in Unity

Graphics Programming

Lecture 03 – Light, Shadows, and Global

Illumination

Edirlei Soares de Lima

<edirlei.lima@universidadeeuropeia.pt>

The Physics of Light

•

Light is electromagnetic radiation of a frequency that can be

detected by the human eye (visible light).

From the optics view, light can be seen as electromagnetic

rays that travel in a straight line from its source.

–

The light source emits rays of light.

When the light hits an object, some of the light bounces off the object.

If the reflected light hits our eyes (or the camera lens) – then we see

the object.

The Physics of Light

•

Regular Reflection occurs when the angle at which light

initially hits a surface is equal to the angle at which light

bounces off the same surface.

–

It occurs only when the rays fall on a highly smooth surface, such as a

mirror.

Irregular Reflection occurs when the rays fall on an irregular

surface and are scattered in different directions.

The Physics of Light

Surface Normals

•

When we simulate light in computer graphics, the object's

surface plays an important role. The surface normal vectors

define how light interacts with the surface.

To a surface at a point P, the normal is a vector that is

perpendicular to the tangent plane to that surface at P.

P

Diffuse Shading

•

Many objects in the world have a surface appearance that is

not at all shiny (e.g. newspaper, unfinished wood, and dry,

unpolished stones).

–

Such objects do not have a color change with a change in viewpoint.

•

These objects can be considered as behaving as Lambertian

objects.

Specular Shading

•

Some surfaces have highlights (e.g. polished tile floors, gloss

paint, whiteboards). These highlights have the color of the

light and move across the surface as the viewpoint moves.

Physically Based Shading

•

Physically Based Shading is a model that seeks to render

computer graphics in a way that more accurately simulates

the flow of light of the real world.

–

Phong has been used by the game industry for a long time, but

nowadays is being replaced by physically-based shading.

–

Unity introduced Physically Based Shading in Unity 5 (2015)

Light in Unity

•

Direct light:

–

Light that is emitted, hits a surface once, and is

then reflected directly into a sensor (a camera).

Indirect light:

–

All other light that is reflected into a sensor,

including light that hits surfaces several times.

•

Real-time lighting:

–

Light calculated at runtime.

Baked lighting:

–

Light calculations that are performed in advance,

saved, and then then applied at runtime.

•

Global illumination:

–

A group of techniques that model both direct and

indirect lighting to provide realistic lighting results.

Types of Light in Unity

•

Point Light:

–

A Light source that is located at a point in the scene and emits light in

all directions equally.

Spot Light:

–

A light source that is located at a point in the scene and emits light in a

cone shape.

Directional Light:

–

A light source that is located infinitely far away and emits light in one

direction only.

Area Light:

–

A light source that is defined by a rectangle in the scene, and emits

light all directions uniformly across its surface area.

Point Light

Spot Light

Directional Light

Area Light

Light in Unity

•

Directional Light:

–

Often used to represent the sun .

–

Has a significant effect on the look of the

scene.

Spot Light, Point Light and Area Light:

–

Usually represent artificial light sources .

–

Their positions are usually determined by

scene objects.

Shadows

•

Shadows appear when light rays are blocked: when an object

is between a light source and another object. It prevents the

light rays from reaching the other object.

–

The fist object casts a shadow on the second one.

Shadows in Computer Graphics

•

In ray tracing rendering, shadows can be added very easily:

–

Light comes from some direction l;

–

When computing the color of a point p on a surface, the point is in

shadow if we cast a ray in direction l and it hits an object. Otherwise,

the object is not in a shadow.

How to implement shadows in

rasterized renderings?

•

Shadow Mapping!

Shadow Mapping

•

Basic idea: if we looked our scene from the view point of the

light source, all of the objects that we can see would appear

in light. Anything behind those objects, however, would be in

shadow.

Shadow Mapping

•

Algorithm:

–

Step 1: render the scene from the light's point of view (without

calculating light, color or any other shading process).

–

Step 2: extract and save (usually in a texture) the depth buffer from

the rendering (z-buffer generated by the projection process).

•

This texture is called shadow map. If there are multiple lights, a separate

depth map must be used for each light.

–

Step 3: perform a normal rendering pass, and when evaluating

whether a fragment is visible to the light source, project its location in

the shadow map and compare the looked-up value d_m_a_p with the

actual distance d to the light source.

•

If the distances are the same, the fragment’s point is illuminated; if the d > d_m_a_p,

that implies there is a different surface closer to the source, so it is shadowed.

Shadow Mapping

Screen-Space Shadow Map

Shadow Map

Rendered Scene

Frame Debugger

•

Window->Frame Debugger

Shadow Mapping – Frame Debbuger

Shadow Map – Light 1

Shadow Map – Light 2

Unity Shadows Settings

•

Shadow quality settings: Edit -> Project Settings -> Quality

Shadow settings per light:

Unity Shadow Maps

•

By default, Unity renders the scene four times per light (cascade

technique). The shadow maps are split into four quadrants,

each being rendered from a different point of view.

Shadow Quality

•

Hard vs. Soft Shadows:

Hard Shadows

Soft Shadows

Shadow Quality

Shadow problems:

•

–

Numerical precision limitations (shadow acne):

No bias

With bias

–

Shadow map resolution:

No blur

With Blur

Shadow Quality

•

Cascades Bands:

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, shadows, and configure global illumination for the

morgue room scene.

–

The scene must have:

•

Emissive ceiling lights;

Indirect lighting;

Shadows;

•

Base Scene: https://edirlei.com/aulas/cg/morgue_room.zip