Advected textures Fabrice Neyret EVASION - GRAVIR / IMAG - INRIA Grenoble, France

Purpose: amplifying fluid simulation

Why not simply increase resolution ? Cost: N log(N) / time step with N=1000^3 Storage Problems with CFD for CG [Lamorlette&Foster 02] Unknown small scale phenomena vs artist desires + phenomenological knowledge

Why not simply increase resolution ? Cost: N log(N) / time step with N=1000^3 Storage Problems with CFD for CG [Lamorlette&Foster 02] Unknown small scale phenomena vs artist desires + phenomenological knowledge

Why not simply increase resolution ? Cost: N log(N) / time step with N=1000^3 Storage Problems with CFD for CG [Lamorlette&Foster 02] Unknown small scale phenomena vs artist desires + phenomenological knowledge

Why not simply increase resolution ? Cost: N log(N) / time step with N=1000^3 Storage Problems with CFD for CG [Lamorlette&Foster 02] Unknown small scale phenomena vs artist desires + phenomenological knowledge

Advecting textures = Advecting u,v [Max&Becker 96, Stam 99] Regeneration  blending 3 dephased textures (illusion of motion)  latency = life duration

Problems with texture advection Choosing the latency Blending textures Sub-animation123

Problems with texture advection Choosing the latency Blending textures Sub-animation123

Problems with texture advection Choosing the latency Blending textures  ghosting effects Sub-animation123

Problems with texture advection Choosing the latency Blending textures Sub-animation123

Problems with texture advection Choosing the latency Blending textures Sub-animation123

1. 1. Advecting textures A latency value is ok for a range of velocities (V)  bad motion illusion if V <  texture stretching if V >

1. Advecting textures Adapting latency locally  Layers of given latency + masks   Local criterion – – cumulated deform = particle integral of |  | – – Target deform d*

1. Advecting textures Adapting latency locally  Layers of given latency + masks   Local criterion – – cumulated deform = particle integral of |  | – – Target deform d* Layer 1: lat1 Layer 2: lat2 (>lat1) Layer 3: lat3 (>lat2)

1. Advecting textures Adapting latency locally  Layers of given latency + masks   Local criterion – – cumulated deform = particle integral of |  | – – Target deform d* 1 2 3

2. 2. Blending textures Image textures Procedural textures

2. Blending textures: image textures What to do ? (morphing ?)

2. Blending textures: procedural textures Our solution:

3. 3. Sub-animation Flownoise [Perlin&Neyret 01]

3. Sub-animation Flownoise for sub-scales  rotations  vorticity spectrum  Kolmogorov cascade

3. Sub-animation Flownoise for sub-scales  rotations  vorticity spectrum  Kolmogorov cascade

3. Sub-animation Flownoise for sub-scales  rotations  vorticity spectrum  Kolmogorov cascade k =  E k0k0k0k0 kkkk sub-grid CFD microscale

3. Sub-animation Vorticity energy transfer through scales  distribution law for ( power law )  only needs to scale it ( estimate ) Our case:  heterogeneous fluid ( locality  no Fourier )  not at equilibrium ( transfer delay  time )  user control  relaxation

3. Sub-animation Vorticity energy transfer through scales  distribution law for ( power law )  only needs to scale it ( estimate ) Our case:  heterogeneous fluid ( locality  no Fourier )  not at equilibrium ( transfer delay  time )  user control  relaxation ( user-defined parameters  k and  k )

Results

Conclusion Mixing lo-res CFD and hi-res animated texture:  A model efficient & controllable Future work: –3D applications: detailed clouds & avalanches –Better flownoise control –Manage empty space –Hardware procedural shader

Advected textures Fabrice Neyret EVASION - GRAVIR / IMAG - INRIA (Grenoble, France)

Sub-animation parameters parameters  k and  k: small  : reactive high  : inertial small  : viscous high  : light

1. Advecting textures

3D