This document discusses how DirectX 11 features were used in Unity to create the short film "Butterfly Effect". It describes technologies like compute shaders, tessellation, physically based shaders, hair rendering, skin rendering, volumetric explosions, and post-processing that enabled high-fidelity graphics. Examples are provided of using compute shaders for particle and fluid simulations, tessellation for hair and opacity mapping, and signed distance fields for fractal and morphed surface rendering. The project involved 25 CG artists and 5 programmers over 14 weeks to create 40 scenes using Unity and DirectX 11.

1. Butterfly Effect
DirectX 11 graphic features
Erland Körner, Technical Artist, Unity Sweden

2. Apr 12, 2013 Page
Who am I?!
• I am Erland Körner
• Unity Stockholm, Sweden
• Graphic Artist on demo-team
• 2 decades AAA background.
EA/DICE - Battlefield and
Mirrors Edge.
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Unity DirectX11
Butterfly Effect
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Unity DirectX11
Summed up
• Realtime shortfilm using Unity.
Research project.
• Unity, Passion Pictures and
Nvidia.
• ˜25 CG Artists (0 Unity
experience), ˜5 Programmers
during 14 weeks production time.
• 40GB Data, 40 scenes, 130 shots.
Using Unity CacheServer.
• DirectX 11 and 64bit Editor.
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Unity DirectX11
Usages in Butterfly effect
• DX11 = Collection of Windows multimedia API’s for games. Available
in Unity 4.x.
• DirectX 11 broadens visual (GPU) scope and fidelity. Eases efforts.
• Compute shaders, Tessellation and 3D Textures
• Enabling us to have Physically based, energy conservative shaders on
environment, skin and eyes
• ...Hair rendering and tessellation
• ...Full screen Post Processing
• ...Volumetric explosions
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Unity DirectX11
Compute shader example 1
• +1 million particles in Unity
• Fully simulated on the GPU,
hardly no pressure on CPU.
• GPU buffer position and
velocity.
• Each particle is a generated
billboard.
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Unity DirectX11
Compute shader example 2
• Fluid simulation.
• Works on 3D textures and
performs simulation.
• Texture describes the density and
velocity.
• To show the result the density 3D
texture is raymarched.
• A gradient texture is also
sampled to provide different color
depending on volume thickness.
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Unity DirectX11
Physically based shaders
• Inspired by Mental Ray
“Architectural” (MIA) shader
• High quality offline rendering
• Suitable for hard-surface materials
• Familiar and intuitive to CG /
non-game artists.
• THE shader for everything!!!
• Energy conserving - Material
follows laws of physics!
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Unity DirectX11
Skin Rendering
• Physically based shading.
• Mimics offline SSS rendering tools.
Top, epidermis and subdermal skin
layers.
• Renders lighting, then blurs, combines,
and adds top- and 2 spec layers.
• Back scatter, based on translucency
layers. Adds intensities into sublayer.
Indirect light from spherical
harmonics.
• Catmull-Clark Subdivision,
not directly Dx11 tessellation.
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Unity DirectX11
Hair and Tessellation
• System designed to be similar
to offline systems.
• Geometry shader. Rendered
using DirectX 11 tessellation.
• Hardware hair geometry
generation.
• Hair defined by Emitter mesh
and Guide hairs in 3d package.
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Unity DirectX11
Filmic Post-Effects breakdown
• Heavy amounts of Post-
processing in every shot!
• ...Motionblur (Velocity blur)
• ...Depth Of Field and Bokeh
shapes
• ...Photographic tonemapping
• ...Bloom (HDR, Specular
highlights and sun reflections)
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Unity DirectX11
Filmic Post-Effects breakdown
• ...Color correction (3D LUT)
• ...RGB channel Noise and grain
• ...Lens distortion
• ..HBAO (Horizon Based
Ambient Occlusion)
• Some already added to Unity
4.1...
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Unity DirectX11
Volumetric Explosions
• Fluid simulation expensive and
hard to control.
• Procedural techniques are practical
on current-gen hardware.
• Fast render volume renderer.
• Can calculate normal as gradient of
distance field, for lighting. Gives AO
approximations.
• Detail added by offset with
“pyroclastic” (Perlin) noise. Shade
based on displacement amount.
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Thanks and credits
• Renaldas Zioma, Aras Pranckevičius, Ole Ciliox, Paulius Liekis, Stefan Sandberg at
Unity
• Simon Green, Jon Jansen an everyone involved of Nvidia
• Passion Pictures
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15. More examples

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Unity DirectX11
Opacity Mapping example
• Fourier Opacity Mapping, for
rendering self-shadowing
effects.
• DX11 Tessellation, for
acceleration.
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Signed Distance Field example 1
• Similar approach as volumetric
explosions.
• Julia fractal. Distance Fields are
surfaces defined
mathematically.
• For each pixel touched is
raymarched a function that
describes the fractal.
• Cubemap and AO sampled with
the normal for added detail.
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Signed Distance Field example 2
• Describes whether camera is on the surface (value 0) or above or
below it.
• Morphed by other functions, like the wave (sin and cos).
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Signed Distance Field example 3
• Sample until reaching back of
the volume to figure out
thickness.
• Dim surface where the volume
is thicker.
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