greeb/navier_wasm

A navier stokes solver in wasm for use in js

threejs_wasm_navier

A 2d navier stoke simulation wasm library stolen from AkinAguda, extended and documented. I just added some helper functions to implement it into a game. This has no visualization component even tho you may find an example here on how to do it in threejs.

Build rust

wasm-pack build --target web

Import

import initFluid, { Fluid, FluidConfig } from '../pkg/navier_wasm';

Fluid

Initiate

TODO: not sure about this, find out how to change/fix this To make the original repo work i had to add await initFluid() before doing anything else.

await initFluid();

The fluid simulation takes a grid of max (u16-2)*(u16-2) so 251*251 todo: not 100% sure if max=256 - 4

Theres a helper function in utils.ts to not exceed these maxes

const = [height, width] = getDisplayDimensions(h.w)

FluidConfig

Initiate a FluidConfig with a diffusion parameter

const fluidConfig = FluidConfig.new(height, width, df);

New Fluid

Create fluid with a timestep parameter

fluid = Fluid.new(fluidConfig, dt);

Simulate

In your animation loop add fluid.simulate()

Add density and velocity

This is the simplest form of interacting with the simulation for an example with mouse interaction and more check out the original repo it has addV and addD fns taking previous mouse positions into account. Just add these to your render loop as well to create continues inflow to the right.

fluid.add_density(fluid.ix(nw/2,hw/2), 100);
fluid.add_velocity(fluid.ix(nw/2,hw/2), 100,0);

Read from simulation

To read from the simulation call

    let densityValue = fluid.get_density_at_index(index);
    let velocityX = fluid.get_velocity_x(index);
    let velocityY = fluid.get_velocity_y(index);

Visualization

Look at the original repo for a full implementation with multiple shaders. In three js the simplest visualization without GLSL would be to render lines at each cell

This could be done like this:

Install three(examples) folder

cd three && yarn

Run it yarn dev

There are two files the sink.ts includes a shader pointMaterial lineMaterial and the line.ts its like the most minimal example possible.

ToDo:

• [] Collisions by cell
  • [] Create a middleware to pass scene elements as collisions to the simulation
• [] Fake 3D/Hill solver create hills in 2d could be done by adding a value from 0-1 to an array for the collision 1 is full blocking and 0 is not blocking

Defaults

DEFAULT_TIME_STEP aka dt = 0.5

DEFAULT_DIFFUSION aka df = 0.5

Errors

Out of bound errors means you probably asked to create a simulation matrix exceeding u16*u16 = u16 use the helper function getDisplayDimensions

Resources

Real-Time Fluid Dynamics for Games by Jos Stam

Fluid Simulation SIGGRAPH 2007 Course Notes by Robert Bridson and Matthias Muller-Fischer

Gonkee's video

3Blue1Brown's video on divergence and curl

The Coding Train's video

Credit

Full credit to: AkinAguda