FluidSim2d

A real‑time FLIP fluid simulation for a 2‑inch round LED pocket watch.

• Claude helped develop an html for being able to see the simulation and make live updates in a browser.
• Personally developed the javascript code to be ran in the html, next is to translate the javascript to c++ code to be ran on an ESP32.
• The plan is to have the physics designed to port cleanly to an ESP32-C3 Super Mini driving a circular addressable‑LED matrix.

Run the simulator

No build step. learn/led-matrix-10.html loads the solver from src/sim.js and the harness from src/engine.js.

• Quickest: open learn/led-matrix-10.html in a browser.
• With live‑reload while editing: run npx live-server from the repo root (so the src/ scripts resolve), then open /learn/led-matrix-10.html.

How it works

It's a FLIP (Fluid‑Implicit‑Particle) solver:

1. P2G — splat particle velocities onto a grid.
2. Forces — add gravity (in the direction the watch is tilted).
3. G2P — read velocities back to the particles (FLIP/PIC blend).
4. Advect — move the particles; bounce them off the circular wall.
5. Push‑apart + cohesion — keep particles from overlapping, and let droplets ball up and break off (surface tension).

To learn, I had Claude help develop an explanation of flip fluids that are fit for my needs in learn/physics-and-code.html.

Hardware plan

• MCU: ESP32 (hardware FPU, dual‑core, plenty of RAM)
• Display: circular addressable‑LED matrix, ~10–24 across in a 2″ circle
• Tilt: an accelerometer/IMU (its gravity vector feeds the sim's gravityDir directly)
• Board: custom round PCB (KiCad project in pcb/)

Status

Working on C++ code now to put on ESP32.

Credit

Idea credit fully given to mitxela. First given the idea from his video here.