CSC418 Computer GraphicsCSC418 Computer Graphics

Animation Principles Production pipeline Keyframe Animation

ReadingsReadings

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

Early AnimationEarly 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.

Principles of Traditional AnimationPrinciples 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

The flour sackThe flour sack

Principles of Traditional AnimationPrinciples of Traditional Animation

From “Principles of Traditional Animation Applied to 3D Computer Animation” by John Lasseter, SIGGRAPH 87

1. Timing Space actions to show mass and personality of characters

2. Slow In and Out Spacing of inbetween frames to achieve subtlety of timing and

movement

3. Anticipation

4. Follow Through and Overlapping Action

5. Arcs Visual path of action

Principles of Traditional AnimationPrinciples of Traditional Animation

6. Secondary Action Action of an object resulting from the motion of another action

7. Squash and Stretch

8. Straight Ahead Action and Pose-To-Pose Action

9. Staging Present an idea so that it is unmistakably clear

10. Exaggeration

11. Appeal

Squash and StretchSquash and Stretch

AnticipationAnticipation

Follow throughFollow through

Follow throughFollow through

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 CCartoon Law Amendment CExplosive weapons cannot cause fatal injuries. They merely turn Explosive weapons cannot cause fatal injuries. They merely turn characters temporarily black and smoky. characters temporarily black and smoky.

Cartoons laws of physicsCartoons laws of physics

Production pipelineProduction pipeline

ScriptScript

CharacterCharactersketchessketches

StoryboardStoryboard 2D animatic2D animatic

Character setupCharacter setupMotion testsMotion tests 3D animatic3D animatic

AnimationAnimationLighting,Lighting,RenderingRendering

CompositingCompositing

Post productionPost production

What can be animated?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…

Keyframing in Cel AnimationKeyframing 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

Keyframing in Computer AnimationKeyframing 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

InterpolationInterpolation

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

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Articulated FiguresArticulated 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)

More on Joint HierarchiesMore on Joint Hierarchies

1.11.11.11.111101.1

111101

)()('

)('

VRTRTTV

VRTTV

Forward and Inverse KinematicsForward 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

Forward and Inverse KinematicsForward and Inverse Kinematics

Consider the above two joint, planar arm. Forward kinematics gives:

Inverting these equations gives the inverse kinematics equations:

)sin(sin

)cos(cos

21211

21211

lly

llx

xllyl

yllxlll

llyx

)cos()sin(

)cos()sin(2

)(cos2

22122

221221

21

22

21

221

What makes IK interesting?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?

What more is there to animation?What more is there to animation?

Coming later to a lecture hall near you…

Physical simulation Spring Mass systems Motion Capture Behavioral Animation

Now…Now…

Videos!