CSC418 Computer Graphics

1. CSC418 Computer Graphics • Animation Principles • Production pipeline • Keyframe Animation

2. Readings • Lasseter, “Principles of Traditional Animation Applied to 3D Computer Animation”. This is a graphics paper version of the famous chapter from the book "The Illusion of Life." • An amazing resource for early animation is the page at the Library of Congress. They have Quicktime movies of many famous, early films! • For a great timeline of the history of animation, see Dan McLaughlin's web page. • Cartoon Laws of Physics

3. Early Animation 1911: Winsor McCay (1867- Spring Lake, Ohio -1934) makes his first film, LITTLE NEMO. McCay, who was already famous for his comic strips, used this film in his vaudeville act. His advice on animation was: " Any idiot that wants to make a couple of thousand drawings for a hundred feet of film is welcome to join the club.“ 1920:19 year old Walter Disney (1901-1966) started working in animation at the Kansas City Slide Company. 1928: Disney creates Mickey Mouse. 1974: First Computer animated film “Faim” from NFB nominated for an Oscar.

4. Principles of Traditional Animation • Developed largely during the early days of the Disney studio • Great reference: The Illusion of Life: Disney Animation by Frank Thomas and Ollie Johnston

5. The flour sack

6. Principles of Traditional Animation From “Principles of Traditional Animation Applied to 3D Computer Animation” by John Lasseter, SIGGRAPH 87 • Timing • Space actions to show mass and personality of characters • Slow In and Out • Spacing of inbetween frames to achieve subtlety of timing and movement • Anticipation • Follow Through and Overlapping Action • Arcs • Visual path of action

7. Principles of Traditional Animation • Secondary Action • Action of an object resulting from the motion of another action • Squash and Stretch • Straight Ahead Action and Pose-To-Pose Action • Staging • Present an idea so that it is unmistakably clear • Exaggeration • Appeal

8. Squash and Stretch

9. Anticipation

10. Follow through

11. Follow through

12. Cartoons laws of physics Cartoon Law IAny body suspended in space will remain in space until made aware of its situation. Daffy Duck steps off a cliff, expecting further pastureland. He loiters in midair, soliloquizing flippantly, until he chances to look down. At this point, the familiar principle of 32 feet per second per second takes over. Cartoon Law IIAny body in motion will tend to remain in motion until solid matter intervenes suddenly. Whether shot from a cannon or in hot pursuit on foot, cartoon characters are so absolute in their momentum that only a telephone pole or an outsize boulder retards their forward motion absolutely. Sir Isaac Newton called this sudden termination of motion the stooge's surcease. … Cartoon Law Amendment CExplosive weapons cannot cause fatal injuries. They merely turn characters temporarily black and smoky.

13. Production pipeline Script Storyboard 2D animatic Character sketches Character setup Motion tests 3D animatic Lighting, Rendering Compositing Animation Post production

14. What can be animated? • Lights • Camera • Articulated figures • Deformable figures • Clothing • Skin/muscles • Wind/water/fire/smoke • Hair • Any variable • Given the right time scale, most things…

15. Keyframing in Cel Animation Key frames • Key poses of an animation sequence • Show important story element or pose • Drawn by lead or senior animator • Capture the general impact of a scene In-betweens • All the cels drawn “in-between” the key frames • Complete the flow of the motion • Normally drawn by junior artist, an “in-betweener” • “in-betweener” may also clean up the keyframes

16. Keyframing in Computer Animation • Based on same idea as in cel animation • Animator specifies keyframes • Computer interpolates between them to create in-between frames • Early keyframe system developed by Burtnyk and Wein working at NFB

17. Interpolation • Linear variation of control variables • Cubic splines • Ease-in ease-out curves • E.g. sine based • Track a path in space • Arc length reparmaterization, velocity curves to control timing

18. Articulated Figures • Represented as a hierarchy of transformation matrices • Root node specifies world coordinates of figure (usually at hip) • Joints normally have 1, 2 or 3 rotational degrees of freedom (DOF) • 3 dof • Gimbal joint (locks) • Ball joint (quaternions)

19. More on Joint Hierarchies

20. Forward and Inverse Kinematics • Kinematics: The study of motion when only position and velocity are considered. • Forward Kinematics • Position is specified by setting value for each dof • Hard to achieve world space constraints • Movement flow (relatively) easy to control • Inverse Kinematics • Specify world space constraints that one or more parts of the skeleton must achieve • Solve for joint angles to achieve these • Good for meeting world space constraints (!), but movement flow can be a problem • Most skeletons are highly redundant, so problem is underconstrained

21. Forward and Inverse Kinematics • Consider the above two joint, planar arm. Forward kinematics gives: • Inverting these equations gives the inverse kinematics equations:

22. What makes IK interesting? • For real characters, most IK problems are highly underconstrained • System is redundant • Subspace of solutions satisfies constraints • What solutions satisfy animator’s goals?

23. What more is there to animation? Coming later to a lecture hall near you… • Physical simulation • Spring Mass systems • Motion Capture • Behavioral Animation

24. Now… • Videos!