GDC 2005

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(No Transcript)
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Postmortem Deferred Shading in Tabula Rasa
Rusty Koonce NCsoft September 15, 2008
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Topics Covered

• Introduction
• Background
• Technical Highlights
• Performance
• Player Metrics
• Demonstration
• Questions and Answers

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Introduction

• What is deferred shading?

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Introduction

• What is deferred shading?
• Deferred shading is a technique for lighting a
  scene as a post process. Typically forward
  shading is used, where lighting is applied to
  each vertex or pixel as it is rendered. With
  deferred shading, material properties about each
  pixel are rendered and per-pixel lighting is
  applied as a post process after the scene has
  been rendered.

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Introduction

• What is Tabula Rasa?

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Introduction

• What is Tabula Rasa?
• Tabula Rasa is a massively multiplayer online
  role-playing game. It is set in a near future
  sci-fi setting, taking the player to alien
  worlds. The pace of the game is fast and similar
  to a 3rd person shooter.

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Background

• Engine features wanted by art/design

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Background

• Engine features wanted by art/design
• Shadows and ability to create dramatic lighting
  (not necessarily in real-time -- lightmaps were
  acceptable)?
• Dynamic light support
• Interior and exterior settings -- with support
  for mixing both within the same map
• Support for many objects (players/creatures/NPCs)
  moving into view at once

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Background

• Constraints

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Background

• Constraints
• Pre-existing forward shading engine that
  supported basic dynamic lighting only
• A lot of art and many shaders already created for
  existing engine
• Minimum system requirements of NVidia FX or ATI
  9600 class hardware

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Background

• Decision

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Background

• Decision
• The existing DX9 based engine would be
  retrofitted to support both forward and deferred
  shading. Forward shading would be the fallback
  for lower end hardware, with deferred shading
  being the preferred render pipeline on higher end
  hardware. All existing art assets could be
  leveraged as-is, without the need to update them.

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Technical Highlights

• Benefits of deferred shading

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Technical Highlights

• Benefits of deferred shading
• Lighting cost is proportional to the number of
  lights and is not proportional to the geometric
  complexity of the scene
• Only visible pixels have lighting computations
  executed on them
• Shaders can have lighting computations cleanly
  separated from the material rendering
• Depth and material properties such as surface
  normals become accessible from shaders
• All lighting is done in real-time. No time
  required to build precomputed light data in the
  map build process designers can see their
  changes in real-time.

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Technical Highlights

• Issues with deferred shading

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Technical Highlights

• Issues with deferred shading
• High GPU memory bandwidth utilization
• High VRAM utilization
• No hardware FSAA support (DX9)?
• Very limited hardware alpha blending support

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Technical Highlights

• Implementation Detail (Deferred)?

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Technical Highlights

• Implementation Detail (Deferred)?
• Material MRT Layout

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Technical Highlights

• Implementation Detail (Deferred)?
• FSAA
• 1) Fake Detect edges and blur them
• 2) Emulation Super-sample by rendering to a
  larger render target and then use the hardware to
  filter the final image down to the desired size

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Technical Highlights

• Implementation Detail (Deferred)?
• Alpha Blending
• 1) Flora/ground cover rendered with alpha test
  scaling is used to transition it in and out
• 2) Hair is alpha tested helmets are common place
  in game
• 3) Alpha blended geometry is rendered after
  deferred shading of opaque geometry completes
  this blended geometry typically does not receive
  lighting and if it does it is not exactly the
  same

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Technical Highlights

• Implementation Detail (Deferred)?
• Shadows
• 1) All shadows use shadowmaps every shadow is a
  true volumetric shadow
• 2) All lights can cast shadows
• 3) Artists control if a light casts a shadow if
  if that shadow updates in real-time or not
• 4) Shadowmap rendering is throttled and done
  based on light priority
• 5) The number of shadows active within a single
  frame is capped

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Technical Highlights

• Implementation Detail (Deferred)?
• Video Memory Management
• 1) All render targets are allocated before most
  other resources
• 2) A shadowmap cache is used a fixed number of
  shadowmaps are allocated for the duration of play
• 3) A render target and depth buffer cache is used

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Performance

• Compatibility

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Performance

• Compatibility
• Deferred Shading (Our Min Requirements)?
• 256MB VRAM
• Pixel Shader 3.0
• MRT Support (4 simultaneous)?
• Deferred Shading (Recommended Requirements)?
• 320MB VRAM
• 50 GB/s GPU Memory Bandwidth (8800 GT, X1900)?

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Performance

• Scalability

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Performance

• Scalability
• Deferred lighting performance is most closely
  tied to the GPU memory bandwidth. The more
  bandwidth, the better the performance.
• Unlike forward shading, deferred shading
  performance is significantly tied to the
  resolution at which the game is played.
• Fortunately, today's GPUs are catching up.
  Sub-200 video cards are offered now by ATI and
  NVidia that well exceed 50GB/s in memory
  bandwidth.

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Performance

• NV Perf HUD Profile
• 8800 GTS (64 GB/s Memory Bandwidth)?
• Max Graphics Settings (FSAA off)?
• 1680 x 1050 Approximate Resolution

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Performance
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Performance
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Player Metrics

• Hardware

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Player Metrics

• Hardware

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Player Metrics

• Graphics Settings

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Demonstration

• Hardware
• NVidia 9600 GT 512MB (120, 57.6 GB/s)?
• Intel Core2 Quad Q6600 _at_ 2.40 GHz
• Vista 64
• 4GB RAM

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Questions and Answers

• Contact Info
• Rusty Koonce
• jrkoonce_at_yahoo.com