ComputerAnimationComputer Animation - University of Oulujiechen/Course/L14/Animation.pdf · Rapid...

C O M P U T E R G R A P H I C SC O M P U T E R G R A P H I C S

Computer AnimationComputer AnimationComputer AnimationComputer Animation

Guoying Zhao 1 / 66Guoying Zhao 1 / 66

C O M P U T E R G R A P H I C S

Basic Elements of Computer GraphicsBasic Elements of Computer Graphics

• Modeling• Modeling– construct the 3D model of the scene

• RenderingR d th 3D d l t th l f– Render the 3D model, compute the color of each pixel. The color is related with lighting, environment, object material and g g, , jso on.

• Animation

Guoying Zhao 2 / 66


Computer Animation

• Animation: is the rapid display of a• Animation: is the rapid display of a sequence of images of 2-D or 3-D artwork or model positions in order toartwork or model positions in order to create an illusion of movement.

• Computer animation: pGraphics & imageprogramming or animation softwarea series of moving imagescurrent frame is the modification based on last frame



Rapid display of a sequence of images

“Visual staying phenomenon” to h i i ff

Guoying Zhao 4 / 6615:20 Computer graphics and Application 2009 S. 4

get the animation effect.


Animation of bird flying



• frame: a static image in animation seq• frame: a static image in animation seq

• Usually, a movie is played with 24 frames per secondframes per second.



Fundamental principles of traditional animation

• Director divides movie script into many breakdowns• Director divides movie script into many breakdowns• Senior animators decide the characters’ sculpts for

breakdowns and draw the key framesbreakdowns and draw the key frames• Assistant animators draw the transition images

between key frames and do the color filling and y gsynthesis

• In 1962, K.Lnowlton from Bel Lab tried to use computer techniques to reduce the work of assitant animators.



Animation

• 2D 3D• 2D 3D– 2D: Mickey and Donald; Lion King;

Mulan…– 3D: Toy Story; Finding Nemo; Shrek; Final

Fantasy– Combination of 2D & 3D: The Olympic Co b at o o & 3 e O y p c

Adventures of Fuwa; Spirited Away…



Softwares

• commercial softwares：– Alias / Wavefront: Alias/Wavefront incAlias / Wavefront: Alias/Wavefront inc.– Maya: Alias/Wavefront inc.

S fti S fti i– Softimage: Softimage inc.– 3ds Max: Autodesk inc.– RenderMan: Pixar inc.–……



Procedures of computer animation

• ① Ideas（Scripts）① Ideas（Scripts）• ② Preprocessing• ③ Scenes and sculpts③ Scenes and sculpts• ④ Materials and light sources• ⑤ Animation⑤ Animation• ⑥ Rendering (movements of images) • ⑦ Playing animation⑦ Playing animation• ⑧ Post processing• ⑨ Animation recording⑨ Animation recording• ⑩ Dubbing (Background music and actors

lines)


)


Key steps

M d liM d liModelingModeling

AnimationAnimation

RenderingRenderingRenderingRendering



Techniques of computer animation

• Key frame• Key-frame• Procedure animation• Physics-based animation

Skeletal Animation• Skeletal Animation• Morphing and deformationp g



Key-frame

• First draw the important images (frames).• Remaining frames are filled with• Remaining frames are filled with

inbetweens.

Interpolation: positions or other parameters



Key frame

• Any parameters• Key parameter• Key parameter

– Determine the parameters which should be controledS t k t– Set n key parameters

– Determine the parametric interpolation curvesDi t li i th t t th t f– Discrete sampling in the curve to get the parameter for each frame



Interpolation of camera positions to get browsing path



Key frame

• linear interpolation• linear interpolation

If t0 = 0, t1 = 1; then x(t) = x0(1-t) + x1t



• Polynomial interpolation– Use n+1 key points for interpolation to get a nUse n+1 key points for interpolation to get a n

degree polynomial interpolation curve



• spline interpolation• spline interpolation

If there are many key points, the degree of generated polynomial interpolation curve would be very high, causing

th ff t S li k l d dGuoying Zhao 18 / 66Guoying Zhao 18 / 66

non-smooth effects. Spline curve can keep low degrees and smoother effects.


Procedure animation

• Movement or deformation of objects can• Movement or deformation of objects can be described by a procedure. E.g. fl iflame, waving water.– Particle systemy– Massive animation

• Some animals e g birds fishes moves inSome animals, e.g. birds, fishes, moves in massive group. Randomicity and regularity.

– Waves animationWaves animation– ……



Particle system（Smoke）



Particle system (gushing water)



Massive animation

Flocking.mov

An animation that was shown at the SIGGRAPH 97 course on Artificial Life


SIGGRAPH 97 course on Artificial Life.


Massive animation



Waves animation

S th i d d l th b i f Si• Synthesized wave model on the basis of Sine wave or Fourier

“Real-Time Synthesis and Rendering of Ocean Water”


ea e Sy t es s a d e de g o Ocea WateJason L. Mitchell 2005


“Real-Time Synthesis and Rendering of Ocean Water”


ea e Sy t es s a d e de g o Ocea WateJason L. Mitchell 2005


Physics-based animation

• Take into account the properties of• Take into account the properties of objects in real world: quality, elasticity, f i i ili h ki i i ld hfriction, utilize the kinetics to yield the movement.



• Simulation of rigid body movementSimulation of rigid body movement– Collision detection– Moving response after collision

• Deformation of elastic objectN i id b d l th k bb– Non-rigid body: cloth, snake, rubber

• Fluid motion• Fluid motion

• Other kinetics modelsOther kinetics models– Simulation of glasses and chinawares fracturing– ……



Rigid body (collision)



Rigid body animationRigid body animation

http://graphics.stanford.edu/~fedkiw/


Ron Fedkiw


Elastic objects animation (Spring)



Elastic objects animation (Cloth)

Cloth can be modeled as “mass-spring model”

Guoying Zhao 34 / 66


Cloth animation

h // hi f d d / f dki / R F dkiGuoying Zhao 35 / 66Guoying Zhao 35 / 66

http://graphics.stanford.edu/~fedkiw/ , Ron Fedkiw


Elastic object animation



Elastic objects (Snake and Snake robots)

“Eric - The Dynamic Worm”Eric - The Dynamic Worm ,by Gavin Miller in SIGGRAPH 88 Film & Video Show


Eric.mov


Fluid simulation (Smoke)

“Real-Time 3D Fluid Simulation on GPU with Complex


Obstacles”. Liu Youquan, Pacific Graphics 2004


Fluid simulation (liquid)

http://graphics stanford edu/~fedkiw/


http://graphics.stanford.edu/ fedkiw/Ron Fedkiw


Fluid simulation

http://www.ageia.comPhysical computation in PPU



Viscoelastic object animation

“A Method for Animating Viscoelastic Fluids”Goktekin Siggraph 2004


Goktekin, Siggraph 2004http://graphics.eecs.berkeley.edu/site_root/papers/Goktekin-AMF-2004-08/


Fracturing rigid body objects

http://graphics.stanford.edu/~fedkiw/Ron Fedkiw

wall1.avi


Ron Fedkiw


Fracturing rigid body objectsFracturing rigid body objects

http://graphics.stanford.edu/~fedkiw/Ron Fedkiw


Ron FedkiwArmadillo_fracture.avi


Skeletal Animation

• Skeletal Animation: to simulate the movements of skeleton objects



• Skeleton: looks simple, but the computation ofSkeleton: looks simple, but the computation of movement is complicated.



• Skeleton: articulated structure; a series of rigid body and jointsbody and joints

• Root jointRoot joint

• Degree of freedom: grequired independent variables to determine a specific structurespecific structure.



Driving methods

• Kinematics model• Kinematics model– Movement of object is independent to the

forces which generate movement. Parameters include position, velocity and acceleration.

• Kinetic model– Movement of object is controlled by the

forces on it and relative movementforces on it, and relative movement parameters are determined by kineticequation


equation.


Kinematics model

• Two solving methods• Two solving methods：– Forward Kinematics

• Determine the position of joints and end points according to given state vectors.

– Inverse Kinematics• Position of end points are set by users and the

state vectors are solved automatically, then get the position of joints. (Goal Driving)



Forward Kinematics

S l i i i l d i t iti l b t f• Solving is simple and intuitional, but for users, it is complicated. Too many DOF.

Using motion captures device to get movement parameters.



Inverse Kinematics

• User interaction is simple• Solving is complicated

"Selectively Damped Least Squares for Inverse Kinematics." Samuel R.


Buss and Jin-Su Kim. In Journal of Graphics Tools, 2005


Kinetic model

• Movement of object is controlled by the forces• Movement of object is controlled by the forces on it, and relative movement parameters are determined by kinetic equationdetermined by kinetic equation.



Morphing and deformation

• Morphing vs deformation• Morphing vs. deformation– Morphing: Giving a source object S and a

destination object D, to smoothly transform S to D. In the smooth transition, middle f f Sframes have the characteristics of both S and D.

– Deformation: to deform a single object and transform it to the required shape.



2D morphing



2D morphing

– (1) Build the relationship between features of IS and ID:C0: IS ID； C1: ID IS；

– (2) P : points in I P : points in I then warping functions W and– (2) P0: points in IS P1: points in ID, then warping functions W0 and W1 are defined as：W0(p0, t) = (1 - t)P0 + tC0(P0);W (p t) = (1 t) C (P ) + tP ; t∈ [0 1]W1(p1, t) = (1 - t) C1(P1) + tP1 ; t∈ [0, 1]

– (3) Get two images at time point t. The middle frames can be generated by interpolating the two images.



2D morphing



2D morphing

S i i hiSource

Source image with similar shape to destination

warping

destination

Destination image

Color interpolation

warpingDestination Destination image

with similar shape to source

p g



2D morphing



3D morphing

• Corresponding of features or vertices between source and destination objects.

“Feature-Based Volume Metamorphosis”Apostolos Lerios, Siggraph 1995


p , gg p


Deformation

• Twisting bending tapering• Twisting, bending, taperingoperators(Barr84)

• Free-form deformation• Free-form deformation– Does not control object, but put object into

Wh d f i thia space. When deforming this space, object is deformed accordingly.

– T.W. Sederberg, S.R.Parry. Free-Form Deformation of Solid Geometric Models.


SIGGRAPH 1986 Vol. 20. No. 4.


FFD



Deformation

• Other methods• Other methods– Axial deformation– Constrain-based deformation– metaballmetaball



Constrain-based deformation

P iti t ii h i Position constrainWithout constrain



Metaball



Computer Animation

• Animation• Animation• Computer Animation• Techniques

Key-frameKey frameProcedure animationPhysics-based animationSkeletal AnimationMorphing and deformation


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