Navier-Stokes fluid simulation explained with Godot game engine

(myzopotamia.dev)

81 points | by myzek 4 days ago ago

18 comments

  • nlawalker an hour ago ago

    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/

  • amarant 17 minutes ago ago

    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

  • genxy an hour ago ago

    The unlinked Jos Stam paper is available from his website https://www.dgp.toronto.edu/public_user/stam/reality/Researc...

  • myzek 4 days ago ago

    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!

    • magicalhippo 4 days ago ago

      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.
      • myzek 3 days ago ago

        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

        • magicalhippo 3 days ago ago

          It made it very fun to play with though :D

    • brandonpelfrey an hour ago ago

      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.

    • nick__m 2 hours ago ago

      excellent article, great vulgarisation and human written !

      Thank you

  • Stevvo 2 hours ago ago

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

  • amelius 2 hours ago ago

    Did they test if it satisfies the relevant conservation laws?

    • brandonpelfrey an hour ago ago

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

      • amelius an hour ago ago

        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.

        • markstock a few seconds ago ago

          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.

  • frankdlc222 4 days ago ago

    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!

  • analog8374 2 hours ago ago

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

    • zamadatix 2 hours ago ago

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

      • analog8374 an hour ago ago

        well android chrome doesn't