1. Animation CS 551 / 651 David Brogan dbrogan@cs.virginia.edu dbrogan@cs.virginia.edu

2. Let’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?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?Is the scene/plot fixed or responsive to user? –What can we automate? Must generate 30 frames per second of animation (24 fps for film) Issues to consider: Is the goal to replace or augment the artist?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?Is the scene/plot fixed or responsive to user? –What can we automate?

3. Animation – A broad Brush Traditional Methods Cartoons, stop motionCartoons, stop motionKeyframing Digital inbetweensDigital inbetweens Motion Capture What you record is what you getWhat you record is what you getSimulation Animate what you can model (with equations)Animate what you can model (with equations) Traditional Methods Cartoons, stop motionCartoons, stop motionKeyframing Digital inbetweensDigital inbetweens Motion Capture What you record is what you getWhat you record is what you getSimulation Animate what you can model (with equations)Animate what you can model (with equations)

4. Computer Animation

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

6. Keyframing From “The computer in the visual arts”, Spalter, 1999 How are we going to interpolate?

7. Linear Interpolation Simple, but discontinuous velocity

8. Nonlinear Interpolation Smooth ball trajectory and continuous velocity, but loss of timing

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

10. Style or Accuracy? Interpolating time captures accuracy of velocity Squash and stretch replaces motion blur stimuli and adds life-like intent Interpolating time captures accuracy of velocity Squash and stretch replaces motion blur stimuli and adds life-like intent

11. Traditional Motivation Ease-in and ease-out is like squash and stretch Can we automate the inbetweens for these? Ease-in and ease-out is like squash and stretch Can we automate the inbetweens for these? “The Illusion of Life, Disney Animation” Thomas and Johnson

12. More squash and stretch

13. Anticipation and Staging Don’t surprise the audience Direct their attention to what’s important Don’t surprise the audience Direct their attention to what’s important

14. Follow Through Audience likes to see resolution of action Discontinuities are unsettling Audience likes to see resolution of action Discontinuities are unsettling

15. Combined

16. Secondary Motion Characters should exist in a real environment Extra movements should not detract Characters should exist in a real environment Extra movements should not detract

17. Interpolation 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 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

18. Interpolation Strengths Animator has exacting control (Woody’s face)Animator has exacting control (Woody’s face)Weaknesses Interpolation hooks must be simple and directInterpolation hooks must be simple and direct –Remember the problems with Euler angle interp? Time consuming and skill intensiveTime consuming and skill intensive Difficult to reuse and adjustDifficult to reuse and adjustStrengths Animator has exacting control (Woody’s face)Animator has exacting control (Woody’s face)Weaknesses Interpolation hooks must be simple and directInterpolation hooks must be simple and direct –Remember the problems with Euler angle interp? Time consuming and skill intensiveTime consuming and skill intensive Difficult to reuse and adjustDifficult to reuse and adjust

20. Examples Sports video games Madden FootballMadden Football Many movie characters Phantom MenacePhantom MenaceCartoons Sports video games Madden FootballMadden Football Many movie characters Phantom MenacePhantom MenaceCartoons

21. Motion Capture Strengths Exactly captures the motions of the actor Michael Jordan’s video game character will capture his styleMichael Jordan’s video game character will capture his style Easy to capture data Exactly captures the motions of the actor Michael Jordan’s video game character will capture his styleMichael Jordan’s video game character will capture his style Easy to capture data

22. Motion Capture Weaknesses Noise, noise, noise! Magnetic system inteference Visual system occlusions Mechanical system mass Tethered (wireless is available now) Noise, noise, noise! Magnetic system inteference Visual system occlusions Mechanical system mass Tethered (wireless is available now)

23. Motion Capture Weaknesses Aligning motion data with CG character Limb lengthsLimb lengths Idealized perfect jointsIdealized perfect joints Foot slidingFoot sliding Reusing motion data Difficult to scale in size (must also scale in time)Difficult to scale in size (must also scale in time) Changing one part of motionChanging one part of motion Aligning motion data with CG character Limb lengthsLimb lengths Idealized perfect jointsIdealized perfect joints Foot slidingFoot sliding Reusing motion data Difficult to scale in size (must also scale in time)Difficult to scale in size (must also scale in time) Changing one part of motionChanging one part of motion

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

26. Procedural www.sodaplay.com http://jet.ro/dismount

27. Examples Inanimate video game objects GT Racer carsGT Racer cars Soapbox about why this is so coolSoapbox about why this is so cool Special effects Explosions, water, secondary motionExplosions, water, secondary motion Phantom Menace CG droids after they were cut in halfPhantom Menace CG droids after they were cut in half Inanimate video game objects GT Racer carsGT Racer cars Soapbox about why this is so coolSoapbox about why this is so cool Special effects Explosions, water, secondary motionExplosions, water, secondary motion Phantom Menace CG droids after they were cut in halfPhantom Menace CG droids after they were cut in half

28. Procedural 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 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

29. Procedural 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 Animation can be generated ‘on the fly’ Dynamic response to user Write-once, use-often Algorithms provide accuracy and exhaustive search that animators cannot

30. Procedural Animation Weaknesses We’re not great at boiling human skill down to algorithms How do we move when juggling?How do we move when juggling? Difficult to generate Expensive to compute Difficult to force system to generate a particular solution Bicycles will fall downBicycles will fall down We’re not great at boiling human skill down to algorithms How do we move when juggling?How do we move when juggling? Difficult to generate Expensive to compute Difficult to force system to generate a particular solution Bicycles will fall downBicycles will fall down

31. Homework Particle Systems Read Particle Systems: A Technique for Modeling a Class of Fuzzy Objects, William Reeves, Siggraph 1983, pp. 359-376Read Particle Systems: A Technique for Modeling a Class of Fuzzy Objects, William Reeves, Siggraph 1983, pp. 359-376 –Movie: Star Trek 2, The Wrath of Khan (Reeves) http://www.siggraph.org/education/materials/HyperGraph/animation/movies/genesisp.mpg –Movie: Particle Dreams (Karl Sims) http://www.siggraph.org/education/materials/HyperGraph/animation/movies/particle75_1_89.mov Implement (by next Tuesday) a simple particle system in OpenGL with a user interface that permits you to control some parameters and to change the viewImplement (by next Tuesday) a simple particle system in OpenGL with a user interface that permits you to control some parameters and to change the view Particle Systems Read Particle Systems: A Technique for Modeling a Class of Fuzzy Objects, William Reeves, Siggraph 1983, pp. 359-376Read Particle Systems: A Technique for Modeling a Class of Fuzzy Objects, William Reeves, Siggraph 1983, pp. 359-376 –Movie: Star Trek 2, The Wrath of Khan (Reeves) http://www.siggraph.org/education/materials/HyperGraph/animation/movies/genesisp.mpg –Movie: Particle Dreams (Karl Sims) http://www.siggraph.org/education/materials/HyperGraph/animation/movies/particle75_1_89.mov Implement (by next Tuesday) a simple particle system in OpenGL with a user interface that permits you to control some parameters and to change the viewImplement (by next Tuesday) a simple particle system in OpenGL with a user interface that permits you to control some parameters and to change the view

32. Homework This homework will be graded simply as done/not-doneThis homework will be graded simply as done/not-done –Camera should pan, tilt, and zoom (at a minimum) –Particles should be physically simulated - f=ma, gravity = -9.8m/s 2, maybe bounce off a surface I don’t care if the code is yours or not, but you want to make sure you can understand and reuse what you submitI don’t care if the code is yours or not, but you want to make sure you can understand and reuse what you submit The next assignment will build on this foundationThe next assignment will build on this foundation This homework will be graded simply as done/not-doneThis homework will be graded simply as done/not-done –Camera should pan, tilt, and zoom (at a minimum) –Particles should be physically simulated - f=ma, gravity = -9.8m/s 2, maybe bounce off a surface I don’t care if the code is yours or not, but you want to make sure you can understand and reuse what you submitI don’t care if the code is yours or not, but you want to make sure you can understand and reuse what you submit The next assignment will build on this foundationThe next assignment will build on this foundation