Real-Time Rendering & Game Technology CS 446/651 David Luebke

Demo Time New card not installed yet so…

Administrative Issues Everything on hold till Thursday –Course forum should be up then, I’ll 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

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?

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

Level of Detail David Luebke University of Virginia

Level of Detail David Luebke University of Virginia

Level of Detail David Luebke University of Virginia

Level of Detail David Luebke University of Virginia

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

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

Level of Detail A recurring theme in computer graphics: trade fidelity for performance –Reduce level of detail of distant, small, or unimportant objects 249,924 polys62,480 polys7,809 polys975 polys

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

Level of Detail: Motivation Big models! –St. Matthew: 372 million polygons –David: 1 billion polygons Courtesy Digital Michelangelo Project

Level of Detail Research: GLOD 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

Courtesy Stanford 3D Scanning Repository 69,451 polys2,502 polys251 polys76 polys Level of Detail: Traditional LOD In A Nutshell l Create levels of detail (LODs) of objects:

Distant objects use coarser LODs: Level of Detail: Traditional LOD In A Nutshell

Level of Detail: The Big Questions l How to represent and generate simpler versions of a complex model? Courtesy Stanford 3D Scanning Repository 69,451 polys2,502 polys251 polys76 polys

Level of Detail: The Big Questions l How to evaluate the fidelity of the simplified models? Courtesy Stanford 3D Scanning Repository 69,451 polys2,502 polys251 polys76 polys

Level of Detail: The Big Questions l When to use which LOD of an object? Courtesy Stanford 3D Scanning Repository 69,451 polys2,502 polys251 polys76 polys

Some Background l History of LOD techniques –Early history: Clark (1976), flight simulators –Handmade LODs  automatic LODs –LOD run-time management: reactive  predictive (Funkhouser) l LOD frameworks –Discrete (1976) –Continuous (1996) –View-dependent (1997)