alt.hn

5/26/2026 at 10:15:28 PM

Navier-Stokes fluid simulation explained with Godot game engine

 https://myzopotamia.dev/navier-stokes-fluid-simulation-explained-with-godot

by myzek

5/30/2026 at 4:00:03 PM

If you haven't tried Animal Well, give it a shot. The whole game and its custom engine are like 35MB and it's filled with really cool visuals and physics powered by fluid equations.

https://store.steampowered.com/app/813230/ANIMAL_WELL/

by nlawalker

5/26/2026 at 10:15:28 PM

So once upon a time I stumbled upon simulating fluids in gamedev and I really wanted to learn how it works. Fast forward 2 months and I decided to write down everything I learned to hopefully make it easier for others in the future!

by myzek

5/27/2026 at 12:54:13 AM

Fluid sims are just so darn fun! Nice writeup, very accessible.

Couple of notes, I think you forgot to apply timestep when adding rocket exhaust velocity, pretty sure it should be

  u[idx] += backward.x * flame_velocity_amount * falloff * delta
  v[idx] += backward.y * flame_velocity_amount * falloff * delta
You need to compensate by scaling up flame_velocity_amount, I used 85, seemed about the same.

by magicalhippo

5/27/2026 at 8:39:54 AM

Yeah it seems I missed that, adding the rocket at the end was a cherry on the top and I was so exhausted already I'm surprised it even works lol

by myzek

5/27/2026 at 10:08:14 PM

It made it very fun to play with though :D

by magicalhippo

5/30/2026 at 3:49:10 PM

Great job. I have spent a lot of time working on fluid simulations (I still am). Glad to see more people still mesmerized. If you’re interested, this rabbit hole goes very deep.

by brandonpelfrey

5/30/2026 at 2:32:57 PM

excellent article, great vulgarisation and human written !

Thank you

by nick__m

5/30/2026 at 5:07:00 PM

Before you go adding vorticity confinement, consider performing a higher-order backward advection scheme (Runge-Kutta 2nd or similar), and using a higher-order interpolation method (triangle-shaped cloud instead of bilinear).

In my implementations I use 4th order for both and vortices stick around a lot longer.

by markstock

5/31/2026 at 4:02:17 AM

If you implement this on the GPU, it's my understanding you can get the 4th-order interpolation quite cheaply exploiting the bilinear texture sampling hardware[1].

So instead of reading 16 grid values and combining them to get the interpolated sample value, you can fetch 4 bilinearly filtered samples and combine those. And thanks to the hardware filtering, those bilinear samples cost basically the same as reading an unfiltered value.

[1]: https://developer.nvidia.com/gpugems/gpugems2/part-iii-high-...

by magicalhippo

5/30/2026 at 3:09:01 PM

For anyone wanting to dive further, Fluid Simulation for Computer Graphics by Robert Bridson is the definitive textbook.

by Stevvo

5/30/2026 at 6:25:49 PM

I appreciate the AI disclosure, I hope that becomes normalized

by jedimastert

5/31/2026 at 8:17:38 AM

I wonder how it'll read in 20 years. Like all the covid references in blog posts from 2020, or vague references to "the current political situation" from any point in the last 10 years or so.

by titanomachy

5/30/2026 at 4:46:09 PM

This is great! When I have some leftover time I want to try copying this implementation for 3D. I reckon I could get away with minimal modifications to support the third axis...I think...

That'll perform even worse though, hopefully my CPU can handle it or I'm gonna need a lot of leftover time to make a shader

by amarant

5/30/2026 at 5:03:39 PM

You are correct: Stable Fluids extends to 3d relatively easily.

by markstock

5/26/2026 at 10:25:59 PM

This is really cool. I love how much detail you went into explaining the setup and walking through each piece of the simulation. Definitely bookmarking this to play around with later!

by frankdlc222

5/30/2026 at 3:17:17 PM

Did they test if it satisfies the relevant conservation laws?

by amelius

5/30/2026 at 3:48:02 PM

It won’t satisfy those laws. It’s also not a goal though of this post.

by brandonpelfrey

5/30/2026 at 4:09:53 PM

I mean if you're writing a ray tracer and the reflected light has more intensity than the light sources, then that's not desired. You can have the same sort of thing going on with a fluid simulation.

by amelius

5/30/2026 at 5:02:24 PM

One of the nice aspects of Stable Fluids is that you don't need to iterate the pressure correction terms to convergence. Just run a fixed number of Jacobi or Gauss-Seidel sweeps and keep performance consistent. The only drawback of this is some mass loss in areas, which for the present purposes is acceptable.

by markstock

5/30/2026 at 8:30:06 PM

Sure, but conservation in ray tracing is also a goal that not everyone has and isn’t required for teaching or games or making pretty & even plausible images. There are plenty of situations in both ray tracing and fluid simulation where conservation is not desirable.

by dahart

5/31/2026 at 1:09:58 AM

Very cool. For your next project, how about a DIY 2D EM field solver? You've done a lot of the work already.

by CamperBob2

5/31/2026 at 12:24:40 PM

AI model latent space needs to be instrumented to a DAW and 3D helical visual effects on triangle slices to show the mathsemantic field gears grinding at the prompt: What's on your mind?

by __patchbit__

5/30/2026 at 2:32:53 PM

Nice writeup. One thing worth adding to the limitations: without vorticity confinement, the Gauss-Seidel projection step quietly dissipates the small-scale curl that makes smoke look like smoke.

The 2001 Fedkiw/Stam/Jensen "Visual Simulation of Smoke" paper added it back as a correction force for exactly this reason. At N=16 it doesn't matter much because the grid itself can't represent fine vortices, but the moment you crank N up the missing confinement becomes visible.

by nryoo

5/30/2026 at 3:02:28 PM

Oh don't let us pinch zoom. That would be a disaster.

by analog8374

5/30/2026 at 3:27:09 PM

Assuming you mean the site - pinch zoom & pan works for me on Windows and iOS?

by zamadatix

5/30/2026 at 3:34:05 PM

well android chrome doesn't

by analog8374

5/30/2026 at 10:08:32 PM

Web exports from Godot (and other game engines) played on mobile is a hard place between compatibility, performance, and many other factors. It's getting better, but very slowly. Try on PC

by OsrsNeedsf2P