Buttefly

Butterfly Effect:Workflow, Rendering & Shading

Renaldas ZiomaUnity Technologies

@__ReJ__

Monday, April 29, 13

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What is it?Real-time animated shortCollaboration between Unity, Passion Pictures and NVIDIA


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Opportunity to Learn

• Passion Pictures• New world of RealTime• No prior experience with Unity

• Unity Technologies• CG Pipeline• Huge amounts of Data

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Project Outline

• 30GB of source Assets• 5GB of runtime Data• 137 shots• 40 “scenes” in Editor

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Project Organization• Team of ~10 - first month

• pre production• research / tools

• Team of ~30 - next 2 months• content• tools / engine modifications

• Team of 5 - last 3.5 months• polish• optimizations

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Previz• One Sequence• Goals

• Initial timings• Visualize Space

• Prime lenses • 10, 14, 18, 21, 24, 27, 35, 40, 50, 75, 100, 200

• Zoom lens • 18 to 150

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Pipeline

• Connect Passion pipeline with Unity Editor• Main Goal

Minimal changes to Artist workflow!

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Passion Pipeline

• No Change for Artists• Use Existing Asset Pipeline

• Sequences SB, BU• Shots SB_01_00, SB_02_00• Assets [Character/Camera/Layout]

• Export Models and Publish Shots as normal• Add Unity support

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Character Rig

• XSI Softimage Rig• Bones• Envelope• Face Shapes• Controls

• Unity Rig• Bones• Blend Shapes• Materials

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Facial Rig

• Bones• Head, neck, jaw, eyes

• Blend shapes • Face

• Mocap shoot• Face markers

• Cubic motion • Retarget facial animation onto XSI controls

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Non-linear time

• Treat Sequences as Live Shoot• Cover the action from different angles• Each sequence needs multiple cameras

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Non-linear time• Shot Description

• Final Cut edit• Export EDL as XML file• Camera in/out points

• Timeline in Unity

• Sequence Preview in RV• Using EDL from Final Cut• Play whole preview sequence in RV• Instant Feedback for Animators

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Timeline in Unity

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Timeline in Unity

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Non-linear Challenges

• Animation• Particles• Physics

• Rigid Body simulation

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Point Cache

• Per-vertex Deformations• Cloth• Hair

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Point Cache


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Tessellation

• CatmullClark• Now: on CPU• Future: OpenSubdiv library

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Hair

• Guide “strands” for modeling• GPU Tesselation and “Amplification”•

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Hair


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MentalRay Architectural (MIA) Shaders• Familiar• Small set of parameters• Physically Based• Micro facet• Energy conserving


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1 parameter for Diffuse


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2 parameters for Specular


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2 parameters for Reflectivity


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MIA Implementation

• Oren-Nayar• Diffuse

• Cook-Torrance• Specular• Geometric + Roughness + Fresnel term• Ward distribution for Roughness• I think... ;)

• Direct + Indirect illumination

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Unity Implementation

• Oren-Nayar• very expensive• OK approximations

• Cook-Torrance• Normalized Blinn-Phong instead of Ward• Roughness to Phong exponent (n):

• n = 2 / roughness2 - 2 • Tweaked to match MIA look:

• n = 2 / roughness4 - 2• Schlick approximation for Fresnel

• Only direct illumination at RunTime

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MentalRay Unity


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Indirect Illumination (GI)

• Point Clouds for Dynamic Geometry• Spherical Harmonics for Diffuse Bounce• Cube Textures for Reflections


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• Textures for Static Geometry• Diffuse Bounce• AO


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• Calculated offline with Autodesk Beast• Path Tracer + Final Gather

• IBL for Sky• Fake Caustics


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Real Time Shadows


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Baked Shadows• Of course baked only for static environments


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Ambient Occlusion• HBAO - Screen Space


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Ambient Occlusion• Too Dark & Dirty


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Ambient Occlusion• Applied ONLY to Indirect Illumination• Colored to match Sky better


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Skin

• Texture Space Diffusion• 3 Layers

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Back Scattering• Translucency Map• Adds intensity to sub-

dermal layer

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HDR

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2 Specular lobes


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HDR

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Depth Of Field

• Antialiasing aware• FXAA based

• With Splatted Bokeh Texture


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Thank you!


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References

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[Bavoil08] Image-Space Horizon-Based Ambient Occlusion. L. Bavoil, M. Sainz, 2008

[Catmull78] Recursively generated B-spline surfaces on arbitrary topological meshes. E. Catmull, J. Clark, 1978

[CookTorrance82] A Reflectance Graphics Model for Computer graphic. R. L. Cook, K. E. Torrance, 1982

[Hoffman10] Crafting Physically Motivated Shading Models for Game Development. N. Hoffman, 2010

[Lottes09] FXAA. T. Lottes, 2009

[Mental07] mental ray Architectural and Design Visualization Shader Library. mental images GmbH, 2007

http://www.mentalimages.com/fileadmin/user_upload/PDF/arch_and_design.pdf

[Mikkelsen09] Microfacet Based Bidirectional Reflectance Distribution Function. M. Mikkelsen, 2009

[Nießner12] Feature-Adaptive GPU Rendering of Catmull-Clark Subdivision Surfaces. M. Nießner, C. Loop, M. Meyer, T. Derose, 2012

[Olano10] LEAN Mapping. M. Olano, D. Baker, 2010

[Schüler11] The Blinn-Phong Normalization Zoo. C. Schüler, 2011

http://www.thetenthplanet.de/archives/255

[Zhukov98] An ambient light illumination model. S. Zhukov, A. Inoes, G. Kronin, 1998






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