Cloud FX



Methods

The difficulty under maya was the fact that you can’t have different level of detail, inside a box of fluid. To make nice clouds we needs 3 level of details (J.Tessendorf):
- Level 1 : The Base = Diffuse clouds without to much detail and with pretty high transparency
- Level 2 : The Cluster = This part need lot more detail and less transparency to get the nice cluster aspect
- Level 3 : Advection = This last part represent the clouds with wispy aspect.

So to implement those 3 levels of detail, i use 3 different BOX of fluids. The base and the cluster were low grid (35,35,35) with texture opacity. For the advection i use a high rez grid of (400,400,400).

The other difficulty is to be able to sculpt the cloud easily and to be able to update the design at any time. For this i use 4 steps.
- Step 1 : You block the volume of your cloud with simple cube
- Step 2 : You fill the cube with simple nurbs sphere with the help of a script
- Step 3 : You create for each sphere a nParticle of the same position and radius
- Step 4 : You use the nParticles to Fill the Fluid

With this method, i get pretty decent result and pretty fast render time (10 minutes per frame for 1280*720)

Reference

Publication :

J.Tessendorf – I Love It When A Cloud Comes Together
D. Batte, M. Fu – Clouds with character: Partly Cloudy
F. Scheepers, A. Angelidis – Atmos: a system for building volume shaders
N. Wang – Realistic and Fast Cloud Rendering

CG Artist :

Srdjan Milosevic – Houdini Artist
Luo Qiulin – Houdini Artist