More Animation Techniques

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Violet Barton
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1 CS 231 More Animation Techniques So much more Animation Procedural animation Particle systems Free-form deformation Natural Phenomena 1

Procedural Animation Rule based animation that

$Animating with noise Grammars and fractals$ Procedural Animation Function-based Animating

2 Procedural Animation Rule based animation that changes/evolves over time. Types of procedural systems: Function-based Animating with noise Grammars and fractals Procedural Animation Function-based Animating with mathematical rules sine, cos,, exp, ln,, etc. Often depends on geometry Scripting 2

3 Animating with noise Perlin invents noise What is noise()? A 'random' function that has statistical properties perceived by the human visual system to include 'appropriate' detail at a variety of scales. Animating with noise Noise adds lifelike feel to models and movement Powerful tool in layering and combining Must model constraints explicitly Animators skill play a heavy hand in success 3

4 Yoichiro Kawaguchi Particle systems Animating complicated systems with many small elements and simple rules Very common method for doing many effects: water spray, explosions, fireworks Rules can include: Distribution rate Movement Color, size, shape Life span, age-related changes 4

5 Particle systems Moving particles (X, V) Particle dynamics Newtonian particles: f = m a a = dv/dt = d 2 x/dt 2 Given f, find the position x so we integrate Can use a simple approximation: v t+1 x t+1 t+1 = a t Dt + v t t+1 = v t Dt + x t Accuracy is not as important as effect! (X, V) 5

Particle systems Movement Applying an (force) acceleration to

accelerations Acceleration toward/away from a point

Tornadoes Particles move in a coherent fashion to produce

6 Particle systems Movement Applying an (force) acceleration to the particles acceleration types include: Random accelerations Acceleration toward/away from a point Acceleration toward/away from a line Spirals, Vortices, Tornadoes Particles move in a coherent fashion to produce overall effect Other prescribed motions (sin(t( sin(t), etc.) Rendering particle effects 6

7 Particle systems Rigging to kinematic model Starting from particle, "rig" follows Procedurally add walk cycle based on velocity turning radius May use IK Particle systems Rigging to kinematic model 7

Free-Form deformation Parametric surfaces are free-form form surfaces. The flexibility in this technique of deformation allows us deform the model in a free-form form manner.

8 Free-Form deformation Parametric surfaces are free-form form surfaces. The flexibility in this technique of deformation allows us deform the model in a free-form form manner. Free-form deformation Embed an object in a deformable region of space. Each point of the object has a unique parameterization that defines its position in the region. When the region is altered, causing recalculation of each points new positions based upon their initial parameterization. 8

9 Free-form deformation Deformation of the lattice then implicitly defines a deformation of the space. Track positions of key points within the deformed sequence of lattices. Free-form deformation Example, single line... Get object Draw polyline Map vertices to polyline Warp polyline s L d Reposition vertices to polyline 9

10 Free-form deformation Free-form deformation Interior angle bisectors Perpendiculars at end points 10

11 Free-form deformation Grid Deformation Overlay 2D grid on top of object Map object vertices to grid cells (create local coordinate system) User distorts 2D grid vertices Object vertices are remapped to local coordinate system of 2D grid by using bilinear interpolation 11

12 Grid Deformation Grid Deformation 0.8 For each vertex Identify cell Local u,v coorindate

13 Grid Deformation P01 Pu1 P11 Bilinear interpolation Pu0 = (1-u)*P00 + u*p10 Pu1 = (1-u)*P01 + u*p11 Puv = (1-v)*P0u + v*p1u P00 Pu0 P01 Grid Deformation 13

14 Grid Deformation Free-Form Form Deformations Define local coordinate system for deformation T U S (not necessarily mutually perpendicular) 14

15 FFD position of point T U S Result 15

16 Result Deform a character arm Hierarchical FFD 16

17 Natural Phenomena Fire, Smoke, Explosions Natural phenomena why? Scale/Money/Complexity? no Problem Control over animation example: face in smoke Natual beauty of the world around us 17

Natural phenomena where is the research? Modeling starts from engineering and physics principles Graphics require only a subset of effects and only visual accuracy.

18 Natural phenomena where is the research? Modeling starts from engineering and physics principles Graphics require only a subset of effects and only visual accuracy. Thus: precision vs. speed Controls sometimes added for animators Rendering often an issue Natural phenomena disaster and destruction Explosions Fire Wind Smoke 18

19 Explosions and modeling of blast waves Explosions and modeling of blast waves Governing principles and equations Compressible fluid dynamics Heat transfer via conductivity, work from pressure, viscous dissipation, convection Ideal gas laws 19

20 Explosions and modeling of blast waves First Law of Thermodynamics Change in energy = heat + work Covers: conduction pressure viscous convection (heat) (work) (work) (e. moves) Explosions and modeling of blast waves Graphical model Voxels for regular grid, as in water simulation Operator splitting solve for ~acceleration/vels without convection Update energy & density w/o convection Recompute vel,, energy, and density Update other variables 20

$temperature Blast affects index of refraction like in$

21 Explosions and modeling of blast waves Rendering model Black-body radiation used to render fireballs, based on temperature Blast affects index of refraction like in real explosions Explosions and modeling of blast waves Results 21

22 Results Animating fire and flames 22

23 Animating fire and flames Governing principles and equations Conservation of mass in fuel consumption Conservation of momentum Density change based on solid/gas transitions in fuel, affects velocity Animating fire and flames Graphical model Fluid modeled again as voxels, imcompressible flow. Include buoyancy forces and vorticity Implicit surface/level set method separates the flame/fire from the surrounding air 23

24 Animating fire and flames Rendering Rendering fire depends on temperature, internal heat Computed based on incandescence taken from internal energy 24

25 Animating the effects of wind, gases, and smoke Animating the effects of wind, gases, and smoke Governing principles and equations Again incompressible flow Hydrodynamic primitives combine to create complex flow Hot gas modeled as 3d fluid with temperature propagation 25

26 Animating the effects of wind, gases, and smoke Foster Animating the effects of wind, gases, and smoke Fedkiw, Stam,, Jensen Added vorticity explicitly From the calculated vorticity,, forces are added back into the navier-stokes 26

27 Animating the effects of wind, gases, and smoke Wind force on an object v T v v N surface (Area = A) F T = A v T, friction constant F N = A v N Animating the effects of wind, gases, and smoke Graphical model For wind, the visual effects come from objects moving For gas as steam and smoke, use voxel based approach 27

28 Animating the effects of wind, gases, and smoke Rendering smoke Scattering based on statistical process Transparency Results 28

29 Natural phenomena a recipe for disaster Starting from physical principles Simplify to appropriate level for needed effect Consider animator handles Make pretty pictures 29

Animation of Fluids. Animating Fluid is Hard

Animation of Fluids. Animating Fluid is Hard Animation of Fluids Animating Fluid is Hard Too complex to animate by hand Surface is changing very quickly Lots of small details In short, a nightmare! Need automatic simulations AdHoc Methods Some simple