UE4 Lightmass for Large Console Games (UE4 Lightmass Deep Dive)

Lightmass Operation
for
Large Console Games
© 2016 SQUARE ENIX CO., LTD. All Rights Reserved.

Osamu Saito
SQUARE ENIX CO., LTD.
Environment Designer
Developing games
full of hopes and dreams

Large Console Game
We encountered various
issues in the
following 3 areas

Note:
This is not a “Success Story”
but rather a discussion of “ongoing” issues.
Because our team is still struggling to solve these issues,
our workflow may change in the future.
If you know of better approaches or methods,
Please let me know (right after this session).

Let’s start with Game

Recreation of a Lounge room

Photo
Unreal Engine4

PhotoDoes it seem like we got
the lighting right?
Unreal Engine4

Photo
Bad Lighting
Unreal Engine4

What’s the problem?

Let’s add a moving object
and you will see.

What is the cause? ?

PLV
Precomputed Lighting Volume

These black dots

PLV(Precomputed Lighting Volume) is
indirect lighting data
which is generated in the space
when using Lightmass

PLV is used to
light dynamic objects.

Errors in PLV
cause strange Lighting

Since most games use dynamic meshes
You should pay attention to PLV when building lighting

This is the cause of the lighting error in the
previous slide

This

Our team’s solution

Re-examine
sampling method
Re-examine
lighting method

We reproduced the lighting error
with static lights

Static Light and Emissive Light
are the most likely
causes of errors in PLV

Static Light
Direct light stored in PLV
Emissive Light
Very poor PLV accuracy

Emissive Light
Static Light
Therefore

Static Light
Emissive Light
Our team decided
to limit their usage

We decided to prohibit the use of
Both static light and Emissive light
with dynamic meshes.

This is unfortunate,
But we have no choice

ILCQ Settings

What is ILC?

ILC Indirect Lighting Cache
Indirect lighting caches
are created
for each dynamic mesh
by referencing the PLV

Point
Sampling: one point
(center of bounding box)
Volume
Sampling: 5×5×5 grid
(equal to bounding box size)
ILCQ
Indirect Lighting Cache Quality

ILCQ
Indirect Lighting Cache Quality
Point
Sampling: one point
(center of bounding box)
Volume
Sampling: 5×5×5 grid
(equal to bounding box size)

ILCQ set to “Point” causes errors

But ILCQ set to “Volume” is ok

As a result, draw cost goes up

As PLV is referenced more, the draw cost increases so
Be careful
when using “Volume” for large, fast-moving objects!

Let’s go back to the previous PLV error

Static Light
Stopped direct light from
being stored in PLV
(our customization)
Emissive Light
Improved PLV accuracy
(From UE4.13 onwards,
PLV uses Adaptive Sampling)

Let’s move on to
the next topic

Console

Console Development
always involves
strict limitations

For example, Memory

Texture pool of Unreal Engine is
1GB by default
1GB

Equal to
4K texture x 50 sheets

Out of this,
how much memory
can actually be used for lighting?

200 MB (1/5)
About 10 4K sheets

For this much area?

No. For this much area!

Our development team’s workaround

Only
“BLUE”
is allowed for Lightmap Density

How much resolution does Lightmap Density
“BLUE” represent?

1m ≈ 5 pixels

In extreme cases
we allow “GREEN”

1m ≈ 20 pixels

How about
“RED”?

No way!
1m ≈ 80 Pixels

We ran into this...

Completely red map was checked in
due to incorrect settings

4GB in Lightmaps alone

Too big to be stored in texture pool
Failed to visualize due to error

Overly large files
caused
server access errors

This upset some people...

If uploaded file size exceeds 1 GB,
our system would send a warning e-mail
1GB

So...

What if we use “BLUE”?

So many Lightmap errors

Intersection errors / UV seam errors
Padding errors / UV grid errors

Creating appropriate Lightmap UVs
helps to reduce errors

We had to compromise
to some extent

Folige lightmap error

Column Lightmap error
Intersection error

If you know of better solutions,
please let us know.
We welcome your advice
or suggestions.

One more difficult topic

Though we said 200MB for this scale...

We actually need to reduce it more

Assuming
we have 30 maps at this size...

Lightmaps alone are
200MB×30 = 6GB

This accounts for more than
1/4 of a Blu-ray disk

That’s too much

Today’s last topc

Large

In my opinion,
this is the most difficult issue

Large project = A large number of people
involved

involved
= simultaneous work

involved
= simultaneous work
= Number of people working on lighting
goes into double digits

Various methods
Different preferences

For consistency,
We needed a standard

We chose
“Illuminance-based Lighting”

What is Illuminance?

“In photometry, illuminance is the total luminous
flux incident on a surface, per unit area. It is a
measure of how much the incident light illuminates
the surface, wavelength-weighted by the luminosity
function to correlate with human brightness
perception. Similarly, luminous emittance is the
luminous flux per unit area emitted from a surface.
Luminous emittance is also known as luminous
exitance.”

“In SI derived units these are measured in lux (lx) or lumens per square
metre (cd·sr·m−2). In the CGS system, the unit of illuminance is
the phot, which is equal to 10000 lux. The foot-candle is a non-metric
unit of illuminance that is used in photography.
Illuminance was formerly often called brightness, but this leads to
confusion with other uses of the word, such as to mean luminance.
"Brightness" should never be used for quantitative description, but only
for nonquantitative references to physiological sensations and
perceptions of light.
The human eye is capable of seeing somewhat more than a 2 trillion-
fold range: The presence of white objects is somewhat discernible
under starlight, at 5×10−5 lux, while at the bright end, it is possible to
read large text at 108 lux, or about 1000 times that of direct sunlight,
although this can be very uncomfortable and cause long-
lasting afterimages.”
Excerpt from Wikipedia
https://en.wikipedia.org/wiki/Illuminance

“It is an index literally for measure of how much the incident light
illuminates the object and used to indicate brightness. If the lit object is
not vertical to the ray as shown in right image, illuminance of the lit
object decreases, so in order to interporate this. The difference
between illuminance and light flux is how to consider the dimension of
the lit object. For example, a book which is closer is darker than the
book which is far away. This phenomane is reffere to as low
illuminance. This is why lux is used to indicate how much the light
illuminates the surface of a desk While candela is used as a unit for an
electric light which is a light source.
The brightness per unit perceived by eyes does not depend on
distance but is directly proportional to illuminance of the object.
However, the brightness per unit perceived by eyes attenuates as the
object gets further if dimension is too small even for the object with
same dimension and illuminance.
Extraction form Wikipedia
https: //ja.wikipedia.org/wiki/%E7%85%A7%E5%BA%A6

In other words, “Brightness”

Illuminance is a unit of human
“brightness perception”
Sunny
100,000 Lux
Cloudy
5,000 Lux
Office
500 Lux
Underground
Parking
30 Lux
Street light
5 Lux
Moon light
0.1 Lux

Why use “Illuminance”?

We were often asked:
“What is the sun’s intensity
in terms of a directional light?”

.... I have no idea

How could we find the answer to this?

This brought us to
“Illuminance”

UE4 uses
various intensity standards for
the 4 respective light types
Unknown value
Unknown value
Lumens
Looks like lumens but
actually unknown value

“Illuminance” is not affected by
the type of light source
because it is a unit for received light

Using “Illuminance”,
the intensity of the sun can be
calculated for either a
Point light or Directional light

Using “Illuminance”
allows lighting in one standard
regardless of light type or material

Now let’s calculate the brightness of
the sun
in terms of Directional light
intensity

This part might be a bit boring
but...

First, create a perfectly diffuse surface
by placing a plane with the following settings:
BaseColor＝1.0 Roughness=1.0
Metal=0.0 Specular=0.0

Then
place a Point light 1m above the surface

Increase intensity until the L value
in HDRVisualize mode reaches 1.0

At this point, the Lumen value of
the Point light is about 1966 lm
1966/4π ≈ 156.45lx
L value of 1.0 is equal to illuminance of
about 156 lx

Next, place a Directional light
pointing directly downwards

We get an L value of 1.0
when the intensity is about 3.15
So a Directional light with intensity of 3.15
corresponds to Illluminance of about 156 lx

Illuminance on a sunny day is 100,000 Lux
Sunny
100,000 Lux
Cloudy
5,000 Lux
Office
500 Lux
Underground
Parking
30 Lux
Street light
5 Lux
Moon light
0.1 Lux

100000/156*3.14 ≈ 2012.8
is the Illuminance value of a Directional Light
for a sunny day

2012.8

Adjust Exposure as necessary

“illuminance” is a standard
which can be applied to
different light types
Unknown value
Unknown value
Lumen
Looks like lumens,
but Unknown value Illuminance

Using “Illuminance” as a standard
makes it easier to use the real world
as a reference

Our team measured illuminance and IBL at
regular intervals from sunrise to high noon

We gathered data on
Sun elevation, sun elevation angle, color
temperature, light volume, and IBL

Lighting environment of each time period was
reproduced on UE4 and checked for accuracy...

We built a standardized light rig

This allowed us to standardize the
various lighting methods and
approaches that were being used

Initial lighting design cost
was reduced

However

Using “Illuminance” as a
standard
caused some errors

16 bit limitation

UE4 GBuffer is limited to
16 bits per channel

Maximum value of 16 bit is “65535”

What happens if we use our previous
2012.8 value Directional Light to light
a sphere with Roughness set at 0.0?

Scene color brightness is blown out
at the highlight point shown above
Infinity!

Conversely, with the value set to 0.001,
debug view and gizmo display are blown out

“Illuminance” as a standard
=
“Reality” as a standard

HDR data of the real world
is too big for 16 bit

What should we do?

Are there better lighting workflows?
Please let us know. We are happy to
hear your suggestions.

Wrap up

Large
CS
Game
Watch out for lighting on dynamic
objects!
Save us, Shinoyama-san!
Limitations are very strict
Somebody please help us with light bake errors!
We are proud of creating our
Illuminance standard!
But the Gizmo burns our eyes ;)

Thank you for listening to
our presentation

Please feel free to ask
questions
UnrealEngine4 is a trade mark or a registered trade mark of Epic
Games.
PARAGON is a trade mark or a registered trade mark of Epic Games.
Blu-ray is a trade mark or a registered trade mark of Blu-ray Disc
Association.
Any other company names and product names used in this document
are trade marks or registered trade marks of the individual companies.

UE4 Lightmass for Large Console Games (UE4 Lightmass Deep Dive)

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