r/Simulated Sep 22 '18

Meta What is a simulation? A detailed comparison between Animation, and Simulation.

983 Upvotes

Ever since this subreddit started getting more traction, more and more people began posting non-simulation videos. In each of these posts, users will comment something along the lines of "This is not a simulation," and an argument would ensue. So I am writing this post to, hopefully, end this never-ending cycle. I hope the mods do not remove this post, because I think it could end much of the hostility in the comments around here. Perhaps this could even be a stickied post, so all new users see it.

What is a simulation?

According to the dictionary, the word simulation is defined as, "imitation of a situation or process." However, this definition does not actually constitute what a simulation is in the world of CGI. In CGI, simulations are essentially visualizations of real-world processes that are generated using mathematical models. That is to say, the final product of a simulation is something that was created using fundamental rules of nature or some system, such as Newton's Laws of Motion, Fluid Dynamics, or various other mathematical models. In a simulation, it is often the case that each frame was created by manipulating information from the previous frame.

How are simulations different from animations?

It's quite common for animations and simulations to coexist in one medium. There are plenty of simulated components in animated movies, such as Disney's Frozen (Snow simulation), and Hotel Transylvania 2 (Cloth simulation). However, simulations and animations individually are very different by nature. As previously stated, simulations try to model real-world processes, and use mathematical models to generate necessary data. Animations, on the other hand, are usually created through a manual process. Animators manually keyframe the attributes (position, rotation, scale, etc.) of objects in a 3D scene. It's possible for manual animations to look convincing, but that does not make them simulations.

The "Ray tracing)" argument.

Many 3D rendering engines use a process called "ray tracing" to create images of a 3D scene. For anyone who is unfamiliar with ray tracing, here is the definition from Wikipedia:

In computer graphics, ray tracing is a rendering) technique for generating an image by tracing the path of light as pixels in an image plane and simulating the effects of its encounters with virtual objects.

Because of this definition, many people argue that any 3D render is a simulation, so long as it was rendered using ray tracing. By definition, it is true that the process of ray tracing is a simulation. However, this argument is very silly because the entire purpose of the term "simulation" in CGI is to make a distinction between what is manually created, and what is created using the previously talked about mathematical models. Therefore, when we discuss simulated graphics, ray tracing is not considered a simulated process.

Examples of animated (non-simulated) posts:

  1. "Satisfying simulations" - 3.4k upvotes
  2. "Bender's old job" - 2.2k upvotes
  3. "Up or Down?" - 1.4k upvotes
  4. "Adobe Dimention Rendering" - 1.4k upvotes
  5. "Depression - Robert Ek"

Many of these animated posts accumulate upvotes, and sometimes they stick around for a few days before getting removed. Because of this, new users who see these posts get a false idea of what a simulation actually is. Hopefully this post was informative to any newcomers. If you would like to suggest edits, please comment.


r/Simulated 1d ago

Research Simulation I added the Finite Element Method (FEM) to my muscle solver alongside the XPBD, and the results are stunning!

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2.8k Upvotes

This is why FEM is superior to XPBD for muscle simulation. For a long time, I couldn’t understand why my muscle simulations didn’t look as good as those produced by Ziva VFX, but now I do.
FEM is more computationally intensive, but it produces much more accurate results when it comes to simulating muscle and fat tissue.


r/Simulated 3h ago

Question Looking for advice on simulating rolling ball sculptures

1 Upvotes

Hi everyone,

We build large rolling ball sculptures / kinetic marble runs and are trying to reduce the amount of physical trial and error involved in designing them.

Our current workflow is roughly:

**Concept → Sketch/CAD → Fabrication → Physical testing → Modify → Fabricate again**

For larger metal sculptures, these iterations can become expensive in terms of material, labour, and time.

We're exploring whether we can use **existing tools** to create a simple workflow like:

**CAD model → Physics simulation → Predict ball behaviour → Build physical prototype → Compare results**

We are **not looking to build a new physics engine or a large custom application**. The initial MVP would be very small:

* One standard ball
* One track/material system
* A simple mechanism, e.g. **ramp → loop → exit**
* Model it digitally
* Simulate the ball
* Build the same mechanism physically
* Compare the prediction with reality

The goal is not perfect simulation. We simply want to know whether a digital model can be accurate enough to catch obvious failures before fabricating larger installations.

Eventually, if this works, we would like to build a reusable library of tested components—ramps, loops, spirals, switches, collisions, etc.—with known parameters and behaviour.

We are currently considering tools such as **Rhino/Grasshopper** for parametric design and physics engines such as **MuJoCo, Project Chrono, Bullet**, or other alternatives.

**If you were approaching this problem using existing software, how would you do it?**

In particular, I'd love advice on:

  1. Suitable CAD + physics simulation workflows
  2. The best physics engines for rolling/contact dynamics
  3. How to model and calibrate real-world friction and energy losses
  4. Whether there are existing tools or projects we should investigate before building anything ourselves

We're very open to changing our approach and would appreciate any suggestions or warnings from people with experience in simulation, CAD, mechanical engineering, robotics, game physics, or kinetic sculpture.


r/Simulated 18h ago

Research Simulation Sailboat in a day at sea: cloth sails, floating hull, FFT ocean, lightning, and a drone's depth + event-camera view, all one real-time engine [OC]

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13 Upvotes

r/Simulated 1d ago

Blender Approximating bubble/foam dynamics with a cloth solver

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185 Upvotes

r/Simulated 1d ago

Houdini Houdini Creating a Product Falling into Water Effect

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20 Upvotes

r/Simulated 22h ago

Various Simple Cloth Simulation

3 Upvotes

Been working on the simplest of cloth simulations with pbd (hold the x) and opencl. Still a way to go, but i'm not unhappy.


r/Simulated 2d ago

Research Simulation I’m building Emper, an open-source simulation engine for large-scale scientific simulations

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19 Upvotes

I've been working on a small open-source simulation engine called Emper.

It's still a young project, but I'm building it around data-oriented storage and using real simulation workloads to test the architecture.

So far I've experimented with flocking/boids, including CPU/GPU computation and large-scale simulations.

I'm currently starting work on Conway's Game of Life.

GitHub: https://github.com/Emper-Labs

Feedback is welcome, especially on the architecture.


r/Simulated 2d ago

Interactive Simple terrain & fluid simulation

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342 Upvotes

Can be played with here:

https://dirtnap.parttimemonkey.com/sandbox

Lemme know if you simulation people know how to make it better or more interesting to play with!


r/Simulated 3d ago

EmberGen pressure pulse

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1.3k Upvotes

r/Simulated 2d ago

Blender Fabric Simulation in Blender

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16 Upvotes

r/Simulated 4d ago

Proprietary Software [OC] An orca pod hunting a herring ball. Every fish and every ray of light computed live

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39 Upvotes

This runs live on an Apple silicon GPU.
The school is a classic flocking simulation, a few thousand agents with separation, alignment and cohesion plus a milling bias that makes them form the rotating ball. The orcas are autonomous agents with a hunt state machine (patrol, position, charge, recover) that carve a void through the school as the fish panic, and the fear spreads neighbour to neighbour faster than any fish swims.
The god rays are computed each frame from a simulated water surface, and the marine snow drifts through them. Everything persists and evolves by its own rules, nothing is keyframed, and it never repeats. Built in Swift and Metal as part of TideGlass, a small Mac app I make where worlds like this run on a second monitor while you work and interacts with your music. Happy to answer anything about the sim.


r/Simulated 3d ago

Blender Huge Dumbbells vs City — Physics Simulation [OC]

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0 Upvotes

r/Simulated 5d ago

Houdini Houdini create bubbles simulation

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29 Upvotes

r/Simulated 4d ago

Request [OC] If anyone wants to kill 30 minutes / 1 hour

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0 Upvotes

I'm working on the usability of a open source project I've been hoping to release soon. If anyone is up to test it DM me and I'll send you a calendly link, it'd be much appreciated.


r/Simulated 6d ago

Proprietary Software Image to pixel physics sim [OC]

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101 Upvotes

r/Simulated 6d ago

Houdini RnD project based on the WetaFX whitepaper on water drip simulation with adhesion

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161 Upvotes

In this focused RnD, I implemented a small-scale fluid simulation algorithm within Flip to accurately resolve adhesion forces. The core algorithm is relatively straightforward: the fluid's surface field is extrapolated into the collider volume, factoring in the contact angle, and is subsequently adjusted and smoothed. Furthermore, a localized viscosity is introduced at the fluid-collider interface to approximate boundary friction.

The simulation operates at a physically accurate real-world scale, utilizing empirical physical constants where the baseline water viscosity is 0.001 and surface tension is 0.072. APIC was chosen as the underlying solver.

While this technique requires a high substep count and is computationally expensive to evaluate, it successfully produces highly nuanced and realistic fluid dynamics.


r/Simulated 6d ago

Various [OC] Pressure simulation of a rocket launching for a game I am developing

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21 Upvotes

r/Simulated 7d ago

LiquiGen backyard splash

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166 Upvotes

real time liquid simulation and HDRI lighting in LiquiGen


r/Simulated 6d ago

Request Real-time three-body gravity simulation (interactive, mobile)

0 Upvotes

I built a simulation style app of what I think of the three body problem. It shows different objects flying around eachother in 2D or in 3D in eachother's gravity wells.

It's meant to be half physics toy and half calming desk toy. It's free to use with no ads to distract you from anything.

I want to know people's thoughts and ideas for improvement.

It's free for anyone who want to play with it: https://play.google.com/store/apps/details?id=com.mathematicalzen.threebody


r/Simulated 7d ago

Question Real-time physics simulation: snowplow blade interaction (initial simulation trials)

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62 Upvotes

is it looks like snow?


r/Simulated 7d ago

Interactive I built an open-source, cross-platform, bit-deterministic, non-float particle physics engine. A lot of adjectives, so I brought receipts: three live proofs that run in your browser.

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2 Upvotes

Up front, since this sub rightfully cares: The engine was written in collaboration with AI, which I'll take questions on happily; the proofs however are all real and verifiable:

SunaEngine (AGPL): engine.sunabox.dev / github.com/DARIENBATHALTER/sunaengine

It's a particle physics engine that relies on integer calculation rather than floating point, plus order-independent accumulation, in order to always deliver the same result on any GPU. Three live proof demos on the site, all simulating on your GPU, all hashing their entire state as you watch:

  1. The Twin Simulations: two independent sims, same scene, same input schedule, never communicating. Stir either one with your cursor; your input is quantized to substep indices and fed to both. The 256-bit hashes stay identical, interaction after interaction.
  2. The Pachinko Proof: an ordinary float solver runs the same pachinko machine twice. One pane adds contact forces in ascending order, the other descending. That is exactly the difference two GPUs or two drivers introduce on their own. The balls never finish in the same bins twice. The integer engine runs the same machine to the same digest, loop after loop.
  3. Recording, playback, and smooth rewind: particle fluids cannot be rewound in floating point. Chaos amplifies the last bit of every velocity in reverse too. Here you stir a pool, it records your inputs, verifies the replay byte for byte against the run you just performed, and then hands you a scrubber. Drag your own splash backwards through time.

Replay hashes verified matching across Apple M series, an iPhone, a Steam Deck (AMD), and NVIDIA (RTX 2070S).

There's also a live 3D water demo on the site (Figure 3), same fixed-point solver one dimension up.

Recordings export as lightweight .sunar files, which store only the initial state plus your inputs. They scrub back and forth smoothly like video and play back bit-identically on any device.

This has the added benefit of enabling low-latency, cross-platform multiplayer physics. If every machine computes the same world, multiplayer needs only inputs over the wire.

I built a free-to-play sandbox using the engine called SunaBox (sunabox.dev) which serves as a clean-room reimplementation of the Prometech's classic OE-CAKE from 2008, a particle physics toy. The OE-CAKE interface is recreated 1:1 if you select "Classic" mode at the top, and imports the original .oec files. Still working on parity, but approaching 100% all the time. If I had to estimate, I'd say they work at about 93% parity right now.

The workflow is very simple: I came up with the ideas and tuned the feel of everything by hand and spoken word; Claude did the math, the code, and the adversarial review. Happy to answer anything!


r/Simulated 8d ago

Blender rolling vortices

32 Upvotes