Maximizing the User Experience

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Maximizing the User Experience A comprehensive
suite of level-of-detail (LOD) techniques for
modern high-end F2P games ?????????????(LOD)????
???????F2P???
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Speaker Introduction

• Christopher Pfeiffer
• Balanced Worlds, CEO
• 14 years in the games industry
• University of Michigan, BSE in Computer
  Engineering

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Games Created????




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Balanced Worlds????????
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LOD BasicsLOD????
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What is LOD?

• Level of Detail
• The goal is to make highly interactive
  experiences while using less resources
• The reduction in complexity comes from graphical
  reductions, algorithmic simplifications, and
  heuristic process culling

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Why is LOD important?

• One reason Quality
• The same game will provide completely different
  player experiences depending on whether its
  running at 15, 30, or 60 FPS
• Greater complexity results in more immersion
• As a game developer, you will never be able to do
  everything that you want to do

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Performance

• All team members must care about the frame rate
• Games are entertainment its ok to deceive the
  player

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Accountability

• Accountability is critical
• Good performance does not happen naturally
• Everyone must know who is reasonable for making
  sure that the frame rate is good

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Budgets

• Performance Budgets MUST be maintained
• If you dont know how much time a system is
  taking during a frame, you dont know if it is
  complete
• Need in-game profiling tools
• Provide testers with tools
• Target your games trouble spots

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2 Common Issues

• Pops!
• Flip- Flop

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Pops!

• Why avoid pops?
• They distract players from the game experience
  
• Types of pops
• Graphical
• Simulation

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Flip-Flop

• Rapid switching between states causes many
  problems
• 2 Methods to resolve it
• Use separate test criteria for entering and
  exiting a state
• Smooth out the metric across frames

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LOD Control MechanismsLOD????
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LOD Selection

• How does the game decide which LOD to use?
• Static methods
• Algorithm selection and fixed parameter values
• Adaptive methods
• Reactive and predictive

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Perception Based LOD

• Trigger LOD changes based on the objects state on
  screen
• Distance squared
• 2d relative speed on screen
• 2d distance from players focal point (the
  reticule)
• 3d depth order
• Drawn or not drawn

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Performance Based LOD

• Metrics
• Simple metrics
• More complex
• The point is that there lot of options available

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User Selected LOD

• Game players want control
• Users often have divergent desires
• Still need to group options to make them
  intuitive

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Specific LOD Types

• Graphical LOD
• Skeletal LOD
• Simulation LOD
• AI LOD

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Graphical LOD??LOD
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Resolution

• Resolution can be thought of a static LOD
• Pixel fill rate
• LODing one feature sometimes affects other
  features LOD requirements

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Shaders

• Shaders
• Pixel pop
• Shader swap often done at model swap time
• Depending on your requirements, there are a
  myriad of possible LOD options

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Model Swapping

• Method
• Assign each LOD of a model a distance range
• Calculate distance from the camera and select the
  LOD
• Improvements
• LOD distances per mesh
• Cross-fade technique

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Model Swapping

• Production
• Artists need to make all of the LOD models for
  each asset
• Artists must adjust both shader and model LODs
  together in-game

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Precomputed Lighting

• 3 Stage Example
• Highest detail-level stores global illumination
  information
• Medium detail-level just stores a color per texel
• Low detail-level is vertex lit faces without a
  texture

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Precomputed Lighting

• To enable blending actually requires 5 shaders!
• Blend between high and medium
• Blend between medium and low

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View-dependant Dynamic Mesh LOD

• Can be used for continuous terrains and other
  models
• Implementing this type of technology represents a
  serious development risk and commitment
• Morphing looks better than switching LOD levels
  instantly
• Obscure it

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Visual Effects LOD

• Visual effects rely on particles and alpha
  blending
• Effects have an interesting cost function
• Which LOD method is best to use depends heavily
  on the type of special effect
• Very time consuming to get it right

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Skeletal LOD??LOD
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Skeletal LOD

• 3 types of bones
• Bones that are manipulated or queried in the AI
• Bones that animate a collision model
• Bones that skin the rendered geometry

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Skeletal LOD

• Sample Update Loop
• Determine the desired movement for all objects
• Compute the actual movements based on collision
• Animate based on actual movement results
• Update physics objects within the scene
• Do post-physics update on each object

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Skeletal LOD

• Production
• Effects model construction
• Limits model fidelity
• Requires testing to verify utilization

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Simulation LOD????LOD
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Physics

• Often physics isnt necessary
• Most physics in games is used for graphical
  flourish
• Simulation fidelity needs to vary by distance,
  view, and the complexity of the scene
• Carefully determine what actually matters

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Artificial Intelligence LOD????LOD
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AI LOD

• AI has many features which can individually LOD
• Decision making
• Movement Simulation

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Reasonable Practices?????
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LOD What Actually Matters

• Worst case scenarios
• LOD techniques cant account for all situations
• Focus on your worst case scenarios and make them
  perform well

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Real-time Visualization

• In-game real-time visualization is a must
• Rapid iteration is needed to achieve the best
  results
• Tweaking is time consuming
• Artists must be empowered to independently
  improve the frame rate

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Double Check Assumptions

• Problems are not always what they seem
• Double-check architectural decisions
• Make sure to properly identify the performance
  issue

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References Useful Links???????
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References Useful Links???????

• LOD Book
• http//lodbook.com/
• Great collection of papers
• http//debian.fmi.uni-sofia.bg/sergei/cgsr/all.ht
  m
• Insomniac Games
• http//www.insomniacgames.com/tech/techpage.php
• Gamasutra
• http//www.gamasutra.com
• Wikipedia
• http//en.wikipedia.org/wiki/Level_of_detail