Hi Guys, Hope you had a great Christmas, I'm already working again on a big FX project starting early Jan (Exciting Times)!!
This RnD was done over 4 Days for me to test my new machine and learn Houdini FLIP, which seems to be one of the leaders in Fluid Simulation for Visual Effects even ILM have picked it up on the film Pacific Rim. and the pipeline of rendering back in Max through Krakatoa,Frost and V-Ray. The basic FLIP setup is from the OceanFX Flat Tank Shelf setup, I got rid of the WhiteWater networks and added them back in later. The Cross is just an cube with an extrude node on to get the cross, the Greeble Pattern is added in Max at Render Time via Greeble Modifier from Max Clanky. The Animation is keyframe not RBD not using VDB Collisions as theres no need, a cross is very simple for fluid interaction. Theres lots of Greeble Cube splash fluid sim tests/RnDs out there, I wonder whos idea it was to use a Greeble Cube I think it was Ghost VFX's I actually asked them about it when I was working for them for a short while. It kinda looks like an Alien Ship from the film Battleship!
Anyway A cross makes a nice splash, theres no custom/increased velocity or vorticity in the sim, its all from the collision, I lowered the gravity a bit for more scale on the Splash, one thing I found with Houdini FLIP which is common in all Fluid Implicit Particle Solvers is that the fluid can be come very stringy even without using viscosity or surface tension. I used droplets enabled in the sim as it creates more of the water drops IE Droplets as you can see which adds a lot more realism to the sim and final shot, Its easy to go a bit overboard with droplets though, you've got to consider meshing them.
Houdini FLIP WhiteWater Sim In Progress (Spray and Foam)
My Inital plan was to Sim WhiteWater but due to not been able to Export it to an Alembic file through Alembic ROP, Houdini Apprentice supports no exporting I was not able to. However I plan to if I get time export it through PRT and use Frost in Max to create lots of small spheres/Tetrahedrons its nearly as fast as VRay Alembic Proxy as it only creates the meshes at RenderTime.
Frost Meshing WIP (To Be Lit By a HDRI through V-Ray Dome Light)
Example Of Using Lots Of Small Tetrahedrons To Create Spray that can be rendred in VRay
The Meshing of the Main Fluid was done by exporting to the amazing PRT ROP and using Frost to mesh with the Zhu/Bridson meshing, I tried to avoid been to blobby but did not want to webby fluid at the same time, I used some radius threshold to cut off some clumps of mesh that did not look nice, No Radius by Velocity though, I need to try it soon! I use a basic Slice to cut off the bottom of the mesh, Note this does NOT mess the Velocity Data up. I extracted the velocites through Magma Flow/Krakatoa and rendered them to an Extra Tex nap using a Vertex Colour Map.
Then this was added to a Refraction pass to create the WhiteWater/Bubble Refraction when water moves at high speeds. Rendered in V-Ray with basic Global Illumination.
Render Comps and Flipbook ( Final, Flipbook, Velocity,Beauty)
Before and After Velocity Shading (This Render has a SeaBed Refraction I was testing also)
While doing this little project I wanted to work on my Water Shader a bit more as I have some possbible large scale water jobs coming up in 2015 and I wanted to get that SubSurfaceScattering Look with using SSS. I started using not so accurate shaders to get more Attenuation which is depth in the shader so you can see objects underwater from the surface, I now use a lot lower IOR (Index Of Refraction) and a bit more fog which creates a much more realistic attenuation affect. The IOR of water in reality is around 1.33 or 1.34 depending, however my aim is to get nice looking shaders for VFX Rather than physically accurate shaders. I also found Bright Coloured Objects are much more vulnerable to the depth affect than darker objects, also its hard to get the attenuation on Fluid Mesh than on a simple plane due to the added faces of thickness, however I do cut my fluid down using Slice in 3DS Max. I did play with SubsurfaceScattering also, its quite quick on my machine, but when you start getting into complex sims it can be 5 times slower and its not really worth the wait right now. Also to Note, I had to manually place a cross matching the anim of the Houdini Cross in Max again due to Houdini Apprentice not letting you export anything, but it was pretty easy to re match to the Fluid Mesh, and then add the Greeble Pattern/Displacement!
Final Sim/Render Info, Also Ocean Shader RnD
Thanks for Looking! Heres a Sneak Peak of my big RealFlow Project in Production right now! Its nicknamed the "Space Pyramid Rise Shot" again trying to push my VFX Skills to the max! PS Check out the Heart Of the Sea Trailer 2 by Ron Howard for some amazing Fluid Sim VFX Shots coming next year, Think Giant Whale Vs A Ship, now thats exciting!!
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