Computing & Information Sciences Kansas State University Lecture 15 of 42CIS 636/736: (Introduction...

Computing & Information SciencesKansas State University

Lecture 15 of 42CIS 636/736: (Introduction to) Computer Graphics

Lecture 15 of 42

William H. Hsu

Department of Computing and Information Sciences, KSU

KSOL course pages: http://snipurl.com/1y5gc

Course web site: http://www.kddresearch.org/Courses/CIS636

Instructor home page: http://www.cis.ksu.edu/~bhsu

Readings:

Disregard This Play aka Bingo: http://www.youtube.com/watch?v=SVtU5OS0c9A

SIGGRAPH 2007 highlights: http://www.youtube.com/watch?v=feBKaTJD-TA

Chapter 5, Eberly 2e – see http://snurl.com/1ye72

Computer-Generated Animation (CGA)Overview



Lecture Outline

Animation Problems

Previsualization

Modeling

Keyframing

Dynamics and Interpolation

Lighting

Fast Previsualization

Modeling

Keyframe Interpolation

Position

Orientation

Scale

Camera Animation



Let’s talk about computer animationLet’s talk about computer animation

Must generate 30 frames per second of animation (24 fps for film) Issues to consider:

Is the goal to replace or augment the artist?What does the artist bring to the project?

Is the scene/plot fixed or responsive to user?What can we automate?

© 2001 Brogan, D., University of Virginia

CS 445 (Undergrad) / CS 645 (Graduate) – Introduction to Computer Graphics



Computer AnimationComputer Animation





KeyframingKeyframing

Traditional animation technique Dependent on artist to generate ‘key’ frames Additional, ‘inbetween’ frames are drawn automatically by

computer





KeyframingKeyframing

From “The computer in the visual arts”, Spalter, 1999

How are we going to interpolate?





Linear InterpolationLinear Interpolation

Simple, but discontinuous velocity





Nonlinear InterpolationNonlinear Interpolation

Smooth ball trajectory and continuous velocity, but loss of timing





EasingEasing

Adjust the timing of the inbetween frames. Can be automated by adjusting the stepsize of parameter, t.





Style or Accuracy?Style or Accuracy?

Interpolating timecaptures accuracyof velocity

Squash and stretchreplaces motionblur stimuli andadds life-likeintent





Traditional MotivationTraditional Motivation

Ease-in andease-out is likesquash andstretch

Can weautomate theinbetweens forthese?

“The Illusion of Life, Disney Animation”Thomas and Johnson





More squash and stretchMore squash and stretch





Anticipation and StagingAnticipation and Staging

Don’t surprise theaudience

Direct their attention to what’simportant





Follow ThroughFollow Through

Audience likes to see resolution of action Discontinuities are unsettling





CombinedCombined





Secondary MotionSecondary Motion

Characters should exist in a real environment Extra movements should not detract





Interpolation [1]Interpolation [1]

Many parameters can be interpolated to generate animation Simple interpolation techniques can only generate simple

inbetweens More complicated inbetweening will require a more complicated

model of animated object and simulation





Strengths Animator has exacting control (Woody’s face)

Weaknesses Interpolation hooks must be simple and direct

Remember the problems with Euler angle interp?

Time consuming and skill intensive Difficult to reuse and adjust



Interpolation [2]Interpolation [2]



Cartoon Physics Homer3D

Adapted from slides © 2001 Brogan, D., University of Virginia


MoviesMovies



ExamplesExamples

Sports video games Madden Football

Many movie characters Phantom Menace

Cartoons





Motion Capture StrengthsMotion Capture Strengths

Exactly captures the motions of the actor Michael Jordan’s video game character will capture his style

Easy to capture data





Motion Capture WeaknessesMotion Capture Weaknesses

Noise, noise, noise! Magnetic system inteference Visual system occlusions Mechanical system mass Tethered (wireless is available now)






Aligning motion data with CG character Limb lengths Idealized perfect joints

Reusing motion data Difficult to scale in size (must also scale in time) Changing one part of motion






Blending segments Motion clips are short (due to range and tethers) Dynamic motion generation requires blending at run time Difficult to manage smooth transition





MoviesMovies

Animating aliens – progress since late 1990s Retargeting motion – SIGGRAPH Highlight reels – SIGGRAPH 2007 and beyond

Adapted from slides © 2001 Brogan, D., University of Virginia




ExamplesExamples

Inanimate video game objects GT Racer cars Soapbox about why this is so cool

Special effects Explosions, water, secondary motion Phantom Menace CG droids after they were cut in half





Procedural AnimationProcedural Animation

Very general term for a technique that puts more complex algorithms behind the scenes

Technique attempts to consolidate artistic efforts in algorithms and heuristics

Allows for optimization and physical simulation





Procedural Animation StrengthsProcedural Animation Strengths

Animation can be generated ‘on the fly’ Dynamic response to user Write-once, use-often Algorithms provide accuracy and exhaustive search that

animators cannot





Summary

Animation Problems

Previsualization

Modeling

Keyframing

Dynamics and Interpolation

Lighting

Modeling


Position

Orientation

Scale



Terminology

Tasks

Previsualization

Modeling

Keyframing

Lighting


Dynamics

Forward – ballistic simulation

Inverse – ballistics (fire control)

Kinematics

Forward – simulation of articulated model

Inverse – control of articulated model

Computing & Information Sciences Kansas State University Lecture 15 of 42CIS 636/736: (Introduction...

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