Computer Animation Guoying Zhao 1 / 66
Basic Elements of Computer Graphics Modeling construct the 3D model of the scene Rendering Render the 3D model, compute the color of each pixel. The color is related with lighting, environment, object material and so on. Animation Guoying Zhao 2 / 66
Computer Animation Animation: is the rapid display of a sequence of images of 2-D or 3-D artwork or model positions in order to create an illusion of movement. Computer animation: Graphics & image programming or animation software a series of moving images current frame is the modification based on last frame Guoying Zhao 3 / 66
Rapid display of a sequence of images Visual staying phenomenon to get the animation effect. Guoying 14:24 Zhao Computer graphics and 4 / 66 Application 2009 S. 4
Animation of bird flying Guoying Zhao 5 / 66
Frame: a static image in animation seq Usually, a movie is played with 24 frames per second. Guoying Zhao 6 / 66
Fundamental principles of traditional animation Director divides movie script into many breakdowns Senior animators decide the characters sculpts for breakdowns and draw the key frames Assistant animators draw the transition images between key frames and do the color filling and synthesis In 1962, K.Lnowlton from Bel Lab tried to use computer techniques to reduce the work of assitant animators. Guoying Zhao 7 / 66
2D 3D Animation 2D: Mickey and Donald; Lion King; Mulan 3D: Toy Story; Finding Nemo; Shrek; Final Fantasy Combination of 2D & 3D: The Olympic Adventures of Fuwa; Spirited Away Guoying Zhao 8 / 66
Softwares Commercial softwares: Alias / Wavefront: Alias/Wavefront inc. Maya: Alias/Wavefront inc. Softimage: Softimage inc. 3ds Max: Autodesk inc. RenderMan: Pixar inc. Guoying Zhao 9 / 66
Procedures of computer animation 1 Ideas(Scripts) 2 Preprocessing 3 Scenes and sculpts 4 Materials and light sources 5 Animation 6 Rendering (movements of images) 7 Playing animation 8 Post processing 9 Animation recording 10 Dubbing (Background music and actors lines) Guoying Zhao 10 / 66
Key steps Modeling Animation Rendering Guoying Zhao 11 / 66
Techniques of computer animation Key-frame Procedure animation Physics-based animation Skeletal Animation Morphing and deformation Guoying Zhao 12 / 66
Key-frame First draw the important images (frames). Remaining frames are filled with inbetweens. Interpolation: positions or other parameters Guoying Zhao 13 / 66
Key frame Any parameters Key parameter Determine the parameters which should be controled Set n key parameters Determine the parametric interpolation curves Discrete sampling in the curve to get the parameter for each frame Guoying Zhao 14 / 66
Interpolation of camera positions to get browsing path Guoying Zhao 15 / 66
linear interpolation Key frame If t 0 = 0, t 1 = 1; then x(t) = x 0 (1-t) + x 1 t Guoying Zhao 16 / 66
Polynomial interpolation Use n+1 key points for interpolation to get a n degree polynomial interpolation curve Guoying Zhao 17 / 66
spline interpolation If there are many key points, the degree of generated polynomial interpolation curve would be very high, causing non-smooth effects. Spline curve can keep low degrees and smoother effects. Guoying Zhao 18 / 66
Techniques of computer animation Key-frame Procedure animation Physics-based animation Skeletal Animation Morphing and deformation Guoying Zhao 19 / 66
Procedure animation Movement or deformation of objects can be described by a procedure. E.g. flame, waving water. Particle system Massive animation Some animals, e.g. birds, fishes, moves in massive group. Randomicity and regularity. Waves animation Guoying Zhao 20 / 66
Particle system(smoke) Guoying Zhao 21 / 66
Particle system (gushing water) Guoying Zhao 22 / 66
Massive animation An animation that was shown at the SIGGRAPH 97 course on Artificial Life. Guoying Zhao 23 / 66
Massive animation Guoying Zhao 24 / 66
Massive animation Guoying Zhao 25 / 66
Waves animation Synthesized wave model on the basis of Sine wave or Fourier Real-Time Synthesis and Rendering of Ocean Water Jason L. Mitchell 2005 Guoying Zhao 26 / 66
Real-Time Synthesis and Rendering of Ocean Water Jason L. Mitchell 2005 Guoying Zhao 27 / 66
Techniques of computer animation Key-frame Procedure animation Physics-based animation Skeletal Animation Morphing and deformation Guoying Zhao 28 / 66
Physics-based animation Take into account the properties of objects in real world: quality, elasticity, friction, utilize the kinetics to yield the movement. Guoying Zhao 29 / 66
Simulation of rigid body movement Collision detection Moving response after collision Deformation of elastic object Non-rigid body: cloth, snake, rubber Fluid motion Other kinetics models Simulation of glasses and chinawares fracturing Guoying Zhao 30 / 66
Rigid body (collision) Guoying Zhao 31 / 66
Rigid body animation Guoying Zhao 32 / 66 http://graphics.stanford.edu/~fedkiw/ Ron Fedkiw
Elastic objects animation (Spring) Guoying Zhao 33 / 66
Elastic objects animation (Cloth) Cloth can be modeled as mass-spring model Guoying Zhao 34 / 66
Cloth animation http://graphics.stanford.edu/~fedkiw/, Ron Fedkiw Guoying Zhao 35 / 66
Elastic object animation Guoying Zhao 36 / 66
Elastic objects (Snake and Snake robots) Eric - The Dynamic Worm, by Gavin Miller in SIGGRAPH 88 Film & Video Show Eric.mov Guoying Zhao 37 / 66
Fluid simulation (Smoke) Real-Time 3D Fluid Simulation on GPU with Complex Obstacles. Liu Youquan, Pacific Graphics 2004 Guoying Zhao 38 / 66
Fluid simulation (liquid) Guoying Zhao 39 / 66 http://graphics.stanford.edu/~fedkiw/ Ron Fedkiw
Fluid simulation http://www.ageia.com Physical computation in PPU Guoying Zhao 40 / 66
Viscoelastic object animation A Method for Animating Viscoelastic Fluids Goktekin, Siggraph 2004 http://graphics.eecs.berkeley.edu/site_root/papers/goktekin-amf-2004-08/ Guoying Zhao 41 / 66
Fracturing rigid body objects http://graphics.stanford.edu/~fedkiw/ Ron Fedkiw wall1.avi Guoying Zhao 42 / 66
Fracturing rigid body objects Guoying Zhao 43 / 66 http://graphics.stanford.edu/~fedkiw/ Ron Fedkiw Armadillo_fracture.avi
Techniques of computer animation Key-frame Procedure animation Physics-based animation Skeletal Animation Morphing and deformation Guoying Zhao 44 / 66
Skeletal Animation Skeletal Animation: to simulate the movements of skeleton objects Guoying Zhao 45 / 66
Skeleton: looks simple, but the computation of movement is complicated. Guoying Zhao 46 / 66
Skeleton: articulated structure; a series of rigid body and joints Root joint Degree of freedom: required independent variables to determine a specific structure. Guoying Zhao 47 / 66
Kinematics model Driving methods 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 movement parameters are determined by kinetic equation. Guoying Zhao 48 / 66
Kinematics model 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) Guoying Zhao 49 / 66
Forward Kinematics Solving is simple and intuitional, but for users, it is complicated. Too many DOF. Using motion captures device to get movement parameters. Guoying Zhao 50 / 66
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 Guoying Zhao 51 / 66
Kinetic model Movement of object is controlled by the forces on it, and relative movement parameters are determined by kinetic equation. Guoying Zhao 52 / 66
Techniques of computer animation Key-frame Procedure animation Physics-based animation Skeletal Animation Morphing and deformation Guoying Zhao 53 / 66
Morphing and 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 frames have the characteristics of both S and D. Deformation: to deform a single object and transform it to the required shape. Guoying Zhao 54 / 66
2D morphing Guoying Zhao 55 / 66
2D morphing (1) Build the relationship between features of I S and I D : C 0 : I S I D ; C 1 : I D I S ; (2) P 0 : points in I S P 1 : points in I D, then warping functions W 0 and W 1 are defined as: W 0 (p 0, t) = (1 - t)p 0 + tc 0 (P 0 ); W 1 (p 1, t) = (1 - t) C 1 (P 1 ) + tp 1 ; t [0, 1] (3) Get two images at time point t. The middle frames can be generated by interpolating the two images. Guoying Zhao 56 / 66
2D morphing Guoying Zhao 57 / 66
2D morphing Source Destination warping warping Source image with similar shape to destination Destination image with similar shape to source Color interpolation Guoying Zhao 58 / 66
2D morphing Guoying Zhao 59 / 66
3D morphing Corresponding of features or vertices between source and destination objects. Feature-Based Volume Metamorphosis Apostolos Lerios, Siggraph 1995 Guoying Zhao 60 / 66
Deformation Twisting, bending, tapering operators(barr84) Free-form deformation Does not control object, but put object into a 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. Guoying Zhao 61 / 66
FFD Guoying Zhao 62 / 66
Other methods Deformation Axial deformation Constrain-based deformation metaball Guoying Zhao 63 / 66
Constrain-based deformation Without constrain Position constrain Guoying Zhao 64 / 66
Metaball Guoying Zhao 65 / 66
Computer Animation Animation Computer Animation Techniques Key-frame Procedure animation Physics-based animation Skeletal Animation Morphing and deformation Guoying Zhao 66 / 66