Simulation in VFX: what is it?
- Alex Iwanoff
- May 6
- 4 min read
Updated: 5 days ago
A digital simulation is what happens when you try to make natural elements behave on cue, in rhythm, under direction. You guide it. Shape it. So that fluid becomes a bottle of wine. So that a specific wave hits a ship at exactly the right moment.
It’s the art of introducing controlled chaos into a scene. Technically speaking, it's the process of using software to recreate physical phenomena by defining rules based on real-world physics, instead of animating it frame by frame.
Fire, smoke, fluids, cloth, hair, destruction — these are the type of elements that are more often than not simulated because animating them manually would be painfully slow, and nearly impossible to make look real.
And the beauty of it is that you can art direct the motion. Give it purpose. Make it serve the narrative, the emotion, the frame. Think of how every superhero cape feels perfectly timed. That’s thanks to CGI. Simulated and sculpted.
But simulation wasn't always possible. It all started at the end of the 1900...
A BIT OF HISTORY
Recently, the Season 2 of Light & Magic in Disney+ was released. The docuseries traces how ILM was built around a simple idea: use technology to help artists do things no one had done before. To push the boundaries of digital effects, at a time when they were still at their embryonic stage.
To do so, George Lucas brought together a team from every corner of creativity and engineering. Artists, animators, sculptors, coders, engineers, tinkerers. People who could imagine the impossible and others who could code the programs to make it real. Among them is Habib Zargarpour, known as ‘the particle guy’.
“Particles have a mind of their own. When you simulate, you have millions of them and you have to just give them general guidelines. You can have forces of attraction, forces that repel or have them collide with things. But you can’t say this particle’s going to do this thing”, Habib Zargarpour, ILM CG Supervisor.
His early work included The Mask (1994), where he had to add a green gas effect whenever a character took off the mask. But the real test came when Spielberg asked: “Can you do a tornado?”. It was for the movie Twister (1996).
That work unlocked something new: water simulation. Enter: The Perfect Storm (2000). A massive challenge. They needed an ocean that could be directed. Which meant it had to be CG. But, as Masi Oka, ILM digital effects artist, said: "human skin and water are the hardest to do with CG".
And it was. The sheer scale of it, pushed both the technology and the artists to the edge. To complete the shots, they used digital layering: rendering multiple simulations separately (waves, ships, foam, splashes) and combining them into the final shot. As explained in the docuseries, it took 90 days of render time to produce one second of final simulation.
“We were creating revolutionary new technology, just so we could digitally drown George Clooney”, Masi Oka, ILM digital effects artist.
Since then, the technology hasn’t stopped evolving, giving artists more control over simulations with every passing year.
CONTROLLED CHAOS
Particle simulation is therefore a process that requires a different mindset than traditional animation. And this is important for filmmakers to keep in mind when working with VFX teams.
“Because tiny variations [...] never repeat and vastly affect the outcome”, Ian Malcolm, Jurassic Parc, 1993.
As Zargarpour previously noted, the artist defines the forces, materials and constraints, but the final result emerges from the physics itself. That’s because simulations rely on a web of interconnected variables, where a single change can ripple through the entire system.
However, today’s tools allow for more control. You can assign a seed to make a sim repeatable, or isolate and modify a section depending on the software. Even so, a minor tweak can still mean days of rework.
Because, at its core, a simulation is still what the name suggests. You’re influencing a system with millions of particles moving in interdependence. In a way, you’re playing God. It's about experimentation. About learning how to nudge the system toward the result you want. And often, there’s more than one path to get there.
And that’s the beauty of it: the unpredictability. The organic, semi-random quality that makes it feel alive. The magic happens when you finally achieve the look you aimed for or, better yet, when something unexpected turns out even stronger.
To have more control over the frames, many productions turn to hybrid approaches: blending simulations with hand animation. This is the case of Davy Jones’ beard in Pirates of the Caribbean. Of the 40+ tentacles, only eight were hand-animated, meaning they could be precisely controlled. The rest were simulated, giving the beard its unsettling, sticky organic motion.
A similar technique was done in The Last of Us (2023), where the cordyceps fungus erupting from infected mouths were part simulation, part animation. The sim brought realism and chaos. The animation brought timing and control, as explained by Espen Nordahl, VFX Supervisor at Storm Studios.
In the end, simulation is what happens when you take something wild (water, fire, cloth, debris) and make it perform. You control it. Art direct it. Which can be as gratifying as it is nerve-wracking. Because let’s be honest: sometimes those particles? They act like they have a mind of their own (again, as the particle guy said himself).
So, what is a sim? It’s the art of introducing controlled chaos into a scene.
Not a plugin. Not a shortcut.
It’s physics, turned into performance.
Artists tweak parameters, shape forces, and build containers for that chaos — until the result feels juuuuuust right.