Real-time content creation with UE4 ray tracing

Real-time content creation
with UE4 ray tracing
Epic Games Japan / Technical Artist Developer Relations
Hiroyuki Kobayashi

#UE4 | @UNREALENGINE
Ray Tracing in UE4.25

Ray Tracing in UE4.25
Production Ready !

Are you sure it’s okay?

I tried to create real-time content
using evry ray tracing function of UE4!

Example:
Train

Ray tracing verification
● Ambient Occlusion
● Global Illumination
● Sky Light
● Reflection
● Translucency
Verification environment RTX 2080ti Full HD

Ray tracing veriﬁcation
Dynamic lighting is important because the train itself keeps moving.
Is it okay to move it in the ﬁrst place?
Does the noise increase?

Ambient
Occlusion

Ray Tracing Ambient Occlusion
Ray TracingSSAO

High quality and good performance.
l though it depends on the resolution, the diﬀerence from SSAO is about 1 to 2 ms.
Ray TracingSSAO

What happens when move the train?

When movedWhen stoped
What happens when
the train moves?
The noise increased a little.

Only AOLit
What happens when
move the train?
There is no problem because it is almost inconspicuous in the Lit mode.

Global
Illumination

Ray Tracing Global Illumination
Summer Winter

Looking at the processing load breakdown...

Sky Light Global Illumination Reﬂection

About 31ms!!

It was heavy...

Brute Force
Sample Per Pixel 4

Type of RTGI
● Brute Force
● Final Gather
We can change from post process volume.

How’s ﬁnal gather?

Final Gather
Sample Per Pixel 4

Final Gather
Sample Per Pixel 4
About 9ms!!

Final GatherBrute Force
What happens when
move the train?

Final GatherBrute Force
What happens when
move the train?
Final gather has problems with movemet

What happens when
move the train?
Sample Per Pixel 64Sample Per Pixel 4
It didn't change much even if I increased the number of samples.

Try lowering the brute force sample per pixel

Brute Force
Sample Per Pixel 1
About 7ms！！

Brute Force
Sample Per Pixel 1Sample Per Pixel 4
It's cleaner with a higher sample size.
But not by much.

Brute Force
The noise stands out when you move.
But not as much as Final Gather.

Final Gather
● Fast
● Not good at movement
Brute Force
● Slow
● not good at movement, but better than ﬁnal gather

Final Gather
● Fast
● Not good at movement
Brute Force
● Slow
● not good at movement, but better than ﬁnal gather
Neither of them are good at
movement!

What do we do then?

Let's adjust the denoiser.

Global Illumination Denoiser
Denoiser related console commands are also available
GI and Sky Light denoisers are common

r.GlobalIllumination.Denoiser.PreConvolution=2
● Increasing the value suppresses noise to some extent, but gives an overall vague
impression.
r.GlobalIllumination.Denoiser.ReconstructionSamples=1
● Noise jaggies can be suppressed by lowering the value

Adjust the denoiser
PreConvolution=2PreConvolution=1
ReconstructionSamples＝1ReconstructionSamples＝16
Even when you move it, it doesn't stand out much!

Sky Light

Ray Tracing Sky Light
Shadow related issues
● Masked material shadow ignores Opacity Mask
● Cast shadow for each material element does not work
● Sky Light looks diﬀerent in reﬂection

Avoid with r.RayTracing.SkyLight.EnableTwoSidedGeometry = 0
Whether to enable shadows for double-sided materials
Turn oﬀ because the shadows of plants etc. may become too dark
Masked material shadow ignores Opacity Mask

Avoid windowpanes that you do not want to cast shadows by making them separate objects
Cast shadow for each material element does not work

With shadowNo shadow
r.RayTracing.Reflections.RayTraceSkyLightContribution=1
Draw skylight shadows in ray tracing reflection
It doesn't look exactly the same without denoising, and it gets quite dark.
Sky Light looks different in reflection

What happens when
move the train?
Not as much as GI, but still stands out when moving

After adjustmentBefore adjustment
Adjust Denoiser
Just like GI, adjust the denoiser to solve the problem!

Reﬂection

What happens when
move the train?
There is a slight increase in noise, but there is almost no problem.

Ray Tracing Reﬂection
Many RT Reﬂections do not look right
● AO
● Denoised Sky Light and Soft Shadow
● SubSurface Scattering
etc

Many RT Reﬂections do not look right

The shadow of the Two Sided
material turns pink

The shadow of the Two Sided material turns pink
Solved by rewriting the shader code!
#if MATERIAL_SHADINGMODEL_SUBSURFACE || MATERIAL_SHADINGMODEL_TWOSIDED_FOLIAGE
uint ShadingModel = GetMaterialShadingModel(PixelMaterialInputs);
if ( ShadingModel == SHADINGMODELID_SUBSURFACE || ShadingModel == SHADINGMODELID_TWOSIDED_FOLIAGE )
{
Payload.CustomData = GetMaterialSubsurfaceData(PixelMaterialInputs);
}
#endif
EngineShadersPrivateRayTracingRayTracingMaterialHitShaders.usf Around line 385

AfterBefore
Scheduled to be ﬁxed in 4.26
Thank you Monsyo and Nori!

Sky Light shadow is not drawn.
Too bright

Sky Light shadow is not drawn and it is too bright
RayTraceSkyLightContribution=1 or
AfterBefore

It gets pretty dark, but ...

It doesn't bother me so much in lit mode

Soft shadows can also be selected,
but they are rough without
denoising

Soft shadows can also be selected, but they are rough without denoising
Distorts normal or is inconspicuous if the material is rough to some extent
LitReﬂection

Soft shadows can also be selected, but they are rough without denoising
Distorts Normal or is inconspicuous if the material is rough to some extent
High RoughnessLow Roughness

I didn't use it this time, but there is also a reﬂection-related denoiser option

Translucency

Ray Tracing Translucency
Many RT Reﬂections and Refraction do not look right
● AO
● Denoised Sky Light and Soft Shadow
● SubSurface Scattering
etc

Refraction of RT Translucency
There is a lot of information that does not appear
accurately, and there is a lot of noise when moving it.

I didn't use Refraction
Turn oﬀ Refraction and operate with Max Refraction Rays 1

It may be usable if it is about Prop with a
small drawing area
I didn't use Refraction

Reﬂection of RT Translucency
Can be used even when Refraction is oﬀ

What happens when
move the train?
Like opaque reﬂection, it doesn't bother you much when you move

Nvidia RTX Branch　https://github.com/NvPhysX/UnrealEngine/tree/RTX-4.25
Translucent drawing is rasterized, and there is also Hybrid Translucency where only
the reﬂective part is ray-traced

Ray tracing veriﬁcation summary
● Sky Light
● Reﬂection
● Translucency

Ambient Occlusion
● Excellent quality and performance

Global Illumination
● Slow performance
● Weak to fast movements
● Real-time is also possible by adjusting the denoiser

Sky Light
● Beware of shadow-related issues
● Weak to fast movements, but improved by adjusting the denoiser like GI

Reflection
● Know what isn't exactly reflected in the reflection
● Adjust Normal and Roughness for areas where roughness is noticeable

Translucency
● Know what isn't exactly reflected in Reflection and Refraction
● It may be difficult to use Refraction in a large area
● We can also turn off Refraction and use only Reflection

A completely dynamic scene has been created!
RTX2080ti
1920 x 1080
About 30fps

Let's move the light

Lighting with
Sun and Sky

Sun and Sky
Simulate lighting from coordinates and time
Sun and Sky documentation
https://docs.unrealengine.com/ja/Engine/Rendering/LightingAndShadows/SunSky/index.html

Sun and Sky
Freely change the time and seasons!
* Winter assets are required to create a snowy landscape

Example:
Jelly Fish

Veriﬁcation content
● Sky Light
● Translucency
● Reﬂection

Veriﬁcation content
● Sky Light
● Translucency
● Reﬂection
Not used this time

Why did se reﬂection for jellyﬁsh?

Because I make jellyﬁsh ...
● I want to express a soft sheer feeling like frosted glass
● I want to use DoF

Because I make jellyﬁsh ...
The internal organs can be seenthrough vaguely
I want to reproduce this

Translucent verification
I want an effect like the Roughness of RT Reflection
Roughness 0.25Roughness 0.0

Unfortunately it is not possible with
ray tracing translucency

If you let the reﬂection ray penetrate, it
will look translucent ...?

How to get through Ray

Tweak normals in materials

Make it translucent using RT Reﬂection
By using the inverted camera vector as the normal ...

Tangent Space Normal needs to be turned oﬀ

Ray ﬂies almost in the opposite
direction

Roughness and Normal are devised
to make it look like frosted glass

It looks transparent, but it is actually treated as an opaque reﬂection
It is drawn ﬁrmly in Depth

It looks transparent, but it is actually treated as an opaque reﬂection
It is drawn ﬁrmly in Depth
DoF can be used!

I was able to express the transparency
and DoF I was aiming for!

Executable file
https://drive.google.com/file/d/1N7K9O1vj6ypwsAB_v6m5k4E2RzPmR5A9/view?usp=sharing
Project
https://drive.google.com/file/d/1nlYv0YoLzNXgeU1sN6BSt5CrB9FKO9M1/view?usp=sharing
Executable file & project is
open to the public

Is it possible to create real-time content
using evry ray tracing function of UE4?

Understand the advantages and disadvantages of
ray tracing and use it appropriately for each project

Advantages and disadvantages of creating ray tracing content with UE4
Advantages
● Dynamic change in lighting
You can easily simulate date and time and seasonal changes by combining with Sun and Sky
Can handle lighting on moving objects such as trains and airplanes
● Physical accuracy
Reﬂection and GI are now accurate and dynamic, enabling expressions that were previously diﬃcult
● Iteration speed
No need to bake, so of course no Light Map
From modeling to checking lighting is much faster

Advantages and disadvantages of creating ray tracing content with UE4
Disadvantages
● Processing load
It is considerably heavier than the conventional functions, including GI
Depending on the scene, even conventional expressions may be able to produce sufficient quality
● Unsupported part
There are parts that I am not good at, such as reflection and translucent reflection
● Noise basically increases when movement is added
I was moving it late this time, but the GI noise was still severe
If it moves faster, another response may be necessary

Thank you!

Real-time content creation with UE4 ray tracing

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