Real-Time Rendering

1
Real-Time Rendering Game Technology

• CS 446/651David Luebke

2
Demo Time

• New card not installed yet so

3
Administrative Issues

• Everything on hold till Thursday
• Course forum should be up then, Ill send out
  mail when it comes available
• At that point you should do the pitch
  assignment
• Thursday guest visit by Dean Abernathy, IATH
• Topic virtual reality for cultural heritage sites

4
To think about

• What are some possible bottlenecks in system
  performance of a graphics/game engine?
• Does it make any difference to sort your geometry
  front-to-back or back-to-front when using a
  depth-buffer?
• Will your textured polygons render faster if
  MIP-mapping is enabled or disabled?
• Does the order that you traverse polygons (i.e.,
  issue vertices using glVertex() or something like
  it) matter?

5
Moral

• Real-time graphics happens on highly custom,
  highly sophisticated hardware
• You have to understand something about how that
  hardware works for the best performance
• In addition to understanding the basic principles
  and algorithms, of course

6
Level of Detail

• David Luebke
• University of Virginia

7
Level of Detail

• David Luebke
• University of Virginia

8
Level of Detail

• David Luebke
• University of Virginia

9
Level of Detail

• David Luebke
• University of Virginia

10
Introduction

• Level of detail (LOD) is an important tool for
  maintaining interactivity
• Focuses on the fidelity / performance tradeoff
• Not the only tool! Complementary with
• Parallel rendering
• Occlusion culling
• Image-based rendering etc

11
Level of Detail The Basic Idea

• The problem
• Geometric datasets can be too complex to render
  at interactive rates
• One solution
• Simplify the polygonal geometry of small or
  distant objects
• Known as Level of Detail or LOD
• A.k.a. polygonal simplification, geometric
  simplification, mesh reduction, decimation,
  multiresolution modeling,

12
Level of Detail

• A recurring theme in computer graphics trade
  fidelity for performance
• Reduce level of detail of distant, small, or
  unimportant objects

13
Level of Detail

• A recurring theme in computer graphics trade
  fidelity for performance
• Reduce level of detail of distant, small, or
  unimportant objects

14
Level of DetailMotivation

• Big models!
• St. Matthew 372 million polygons
• David 1 billion polygons

Courtesy Digital Michelangelo Project
15
Level of Detail ResearchGLOD

• GLOD
• High-level library for LOD in OpenGL
• Goal make high-quality LOD easy to integrate in
  games and other graphics applications
• Includes and interfaces with VDSlib
• Cool software (interface design) issues
• Free membership in the Church of Glöd
• Show GLOD video

16
Level of DetailTraditional LOD In A Nutshell

• Create levels of detail (LODs) of objects

69,451 polys
2,502 polys
251 polys
76 polys
Courtesy Stanford 3D Scanning Repository
17
Level of DetailTraditional LOD In A Nutshell

• Distant objects use coarser LODs

18
Level of DetailThe Big Questions

• How to represent and generate simpler versions of
  a complex model?

69,451 polys
2,502 polys
251 polys
76 polys
Courtesy Stanford 3D Scanning Repository
19
Level of DetailThe Big Questions

• How to evaluate the fidelity of the simplified
  models?

69,451 polys
2,502 polys
251 polys
76 polys
Courtesy Stanford 3D Scanning Repository
20
Level of DetailThe Big Questions

• When to use which LOD of an object?

69,451 polys
2,502 polys
251 polys
76 polys
Courtesy Stanford 3D Scanning Repository
21
Some Background

• History of LOD techniques
• Early history Clark (1976), flight simulators
• Handmade LODs ? automatic LODs
• LOD run-time management reactive ? predictive
  (Funkhouser)
• LOD frameworks
• Discrete (1976)
• Continuous (1996)
• View-dependent (1997)