Alien Fluid Transition

The Predecessors

I will now present some projects, tests and R&Ds that lead up to how I both got to the idea of making this project as well as how I was able to make it all.

Ice Growth

A few months ago I got interested in trying to make a growth solver for sort of a magical ice effect, that got me to use volumes in conjunction with polygonal geometry in creative ways to be able to make the effect. 

Nightcrawler Vanish

This was a test I made after the Ice Growth project.
I got the idea while I was watching Gen V and there was a character there that had Nightcrawler-like superpowers so I thought about how I would be able to do this effect myself, what I ended up with is getting rid of the geometry on a certain frame and replacing it with a volume that is as similar as I can to the geometry, transferring the velocity and adding some forces so it's a little more interesting.

Then I thought for fun that I could try switching him with fluid instead of smoke and seeing what that looks like. Workflow was very similar.

Sparks

Here's one of the R&Ds I did for creating sparks, this one being specifically sparks that occur from a hit or an impact, which is what I use in the project. The workflow consists of creating points using a curve for 1 frame with space of 2-3 frames in between the points, so I only have 1 point active in any given frame, then replicating that point and using a particle system to shoot those points out, then making a trail out of those points. 
Finally I use the attribute I get from the points colliding with anything to create an extra smaller burst of sparks.

The General Idea

I wanted to get a little more sophisticated than simply removing the geometry at a certain frame and replacing with the volume object like I did with my Nightcrawler test.
For this one, I will be making a VDB from the main body as well as one from the fluid, during the transition phase I slowly cut out more from the front of the body from the VDB made of the actual geometry, and do the opposite for the VDB made from the simulation.

That way I can do a union on both of those VDBs and have the transition be as seamless as possible. Later in compositing I will fade between the render of the geometry itself, which I will use before I need the VDB mesh, into the transitional mesh I created from VDBs, until eventually all we see is the simulation.

Preparing The Model

Here is a comparison between what the model looks like and a frame mid-transition where the legs are still a mesh based on the model and the rest of the body is FLIP particles meshed together with VDB operations.

This is the main geometry before and after cutting it to union with the Particle VDB later.

You can see we're losing some details and there's a small seam where they're being unionized but once we add color and especially during movement, both things aren't noticeable.

The Simulation

After some attempts the best way I found to keep the fluid close to what the original geometry is was to add the velocities as necessary, so I cut out the part I need for the transition so I only get those velocities when I transfer them onto my simulation.

This is my DOPNET for the FLIP simulation. I use a curve that goes straight through the grate in my wall for the main suction forces, then I have another curve force for fine tuning.
I'm adding some slight random forces and then I'm using simple volume velocities I made using smoke to assist in sucking in the fluid and into the grate. Finally adding some drag for the entire simulation and another drag that only works for a few frames during the impact so the fluid doesn't splash too far away.

As for the source, I source the entire thing on the same frame, and control the velocities through the SOP Solver.

I'm bringing in the velocities I cut out earlier and transfer them on my simulation, once there's no more need for those velocities I switch that out.

I then have a box on the other side of the grate under it that is used to group the particles and purge them for optimization.

In order to make the emissive parts properly emissive, I separated them by removing all the parts that had too low of an "emit" attribute.

I then used that geometry for a mesh light, and rendered it separately to be used in compositing later.

Fluid Mesh

Sticky Lines

To make the fluid feel more connected to the wall I added very thin sticky lines that will stick between the wall and the fluid, before eventually tearing apart and go back to the main body of fluid.

To start, I manually placed some points on the wall and gave them an attribute that I can then use to easily make a line out of with a chosen point from my fluid simulation.
I then picked some points from the fluid simulation and kept them using my id attribute, transferred over the "merge" attribute from my manually placed points and connect them into lines.

Then, after getting a curveu attribute by resampling the lines, I give them a slight sag around their middle point for the Y attribute. This is to give them a bit more of a simulated feel without actually having to simulate anything.

I then split those lines into many carve nodes, and use an expression to carve out the outer side of the lines according tot he frames I provide, that way I get the effect that the lines are being drawn back into the main body of fluid.

I resample the points again after the carve and make the scale of the lines for meshing through VDbs to be according to the graph. I make it thick on the edges and very thin in the middle area. I then mesh the lines using VDBs and convert them back into polygons.

Finally, I transfer over the velocity attribute and the color attribute for rendering.

The Compositing

At the start of the scene most of the renders were done separately, as I needed to then transition between the character and the fluid version of the character.
Here you can see the first shot where I have the bullet tracers, character and some of the background elements added to the separately rendered environment.

Here's a frame I composite together between my character and the fluid, I have a feathered mask switching between the two and motion blur does the rest of the job to hide the transition as best as possible.

Here is a small breakdown of the added glows in compositing as well as a wet map.
The glows were made through a combination of both singling out the lighter areas of the rendered fluid, as well as the light pass I rendered using a mesh light.

Thanks for taking your time to look through my submission!