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Introduction to Direct3D 10 Course

• Porting Game Engines to Direct3D 10 Crysis /
  CryEngine2Carsten Wenzel

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Overview

• Introduction
• D3D10 CryEngine2
• Porting, integration issues and optimizations
• Random bits
• Conclusion

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Introduction

• Early adaptation
• Spec reviews / discussions started in 2005
• Actual work began middle 2006
• Support from MS and IHVs was crucial

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D3D10 in context of a multi-platform engine (1/3)

• API redesign offers a more concise view on how
  modern graphics hardware works
• For the sake of performance it offloads a lot
  of responsibility to the API user

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D3D10 in context of a multi-platform engine (2/3)

• CryEngine2 is designed to be multi-platform
• Render implementations share one interface and a
  lot of common code
• State resource management
• Draw list processing
• Shader subsystem, etc.

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D3D10 in context of a multi-platform engine (3/3)

• Certain API changes required special
  consideration
• State objects
• Shader model 4.0
• Constant buffers
• Strict API validation (shader linkage, etc)
• Buffer updates
• Support for new features
• E.g. Geometry Shader, Stream Out, Texture Arrays

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Porting and making it work (1/2)

• Render code separates platform / API dependent
  parts from independent parts
• D3D10 renderer specializes base renderer
• Inherits interface and all common code

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Porting and making it work (2/2)

• Platform / API dependent parts wrapped and called
  from common code
• Provided stubs implemented one at a time
• ifdef where API characteristics were awkward to
  map to common code flow

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Special considerations (1/5) State objects

• Need fine grained control over render states!
• Wrap state manipulation
• Internally caches state objects
• Currently build state objects on demand
• Pre-warming cache might be worthwhile

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Special considerations (2/5) Shader model 4.0

• Use custom shader / effect system
• Updated to support new API features and enhanced
  HLSL syntax
• Query resource bindings via Shader Reflection
• Compile existing shaders as is (/Gec)
• Refactored to utilize load balancing
• Still use shader cache

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Special considerations (3/5) Constant buffers

• Group constants by frequency of update
• Each group maps to a unique CB index
• Constants bound via semantic which encodes group
  id
• Allows preprocessor to move constants into their
  appropriate CB scope
• Existing shaders automatically benefit from
  efficient binding
• Source shader scripts devoid of API specific
  annotations
• Shader authors dont have to worry about API

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Special considerations (4/5) Strict API
validation

• API rigorously checks how user drives it
• Simplifies lower API / driver levels
• Example Shader linkage
• Vertex layout / output signature has to match
  input signatures of following shader
• Dimension of each passed element has to match
  dimension expected in following shader
• Took some time to clean up / unify signatures
• Nice side effect Signature-fixed shaders run
  faster on DX9

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Special considerations (5/5) Buffer updates

• Update methods for truly static / dynamic buffers
  remain as in D3D9
• Occasional updates of static buffers can cause
  severe pipeline stalls(e.g. updating terrain)
• Staging resources as intermediate storage
• This way mesh update can be pipelined

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Random DX10 bits used in CryEngine2

• GS used for particles and shadows
• Viewports for texture atlas
• Filtered texture lookups in vertex shader (FFT
  water)
• Multi-sampled texture lookup(HDR
  post-processing)
• Sample depth from z buffer
• Render to volume texture

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Conclusion

• New D3D10 features are great
• Perf improvements are definitely there
• Expect several code revisions to drive the API in
  the most efficient way

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More details

• 1 Finding Next-Gen, Martin Mittring, SIGGRAPH
  2007
• Part of course 28, Advanced Real-time Rendering
  in 3D Graphics in Games
• Wed Aug 8th, Room 7AB, 830 am - 530 pm
• 2 Real-time Atmospheric Effects in Games
  Revisited, Carsten Wenzel, GDC 2007
• Slides and course notes available online

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Acknowledgements

• Crytek RD Graphics Group
• Many thanks to MS, NVIDIA and ATI for the support

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Questions?