t4as

Software & Sims · 2026

Sim Env v1: Browser Evolution Sandbox

The first version of Sim Env: an evolution sandbox in C++ and raylib, compiled to WebAssembly so it runs in the browser. Creatures with pixel bodies and neural brains evolve three feeding strategies with no programmed goals.

  • C/C++
  • raylib
  • WebAssembly
  • Emscripten
Play in browser
Sim Env v1 zoomed in: small pixel-body creatures with their vision lines and targets on a tiled light map

What it is

Sim Env v1 is a small evolution sandbox built on raylib and compiled to WebAssembly with Emscripten, so it runs in the browser with nothing to install. Creatures have bodies made of pixel cells and a neural brain fed by vision rays. Nothing is programmed beyond survival: creatures that gather energy reproduce, the rest die.

It was the starting point for the current version, Sim Env: Open-Ended Evolution, which rebuilt the engine from scratch and now runs as an always-on world you can watch live.

How it works

Three feeding strategies

Photosynthesis (absorbs light from the light pools), mouths (eat ground nutrients) and spikes (drain energy from prey). Which one a lineage uses emerges from its body.

Pixel bodies

Each creature is a 13×13 grid of cells: structure, thrusters in several directions, sensors, mouths, spikes and photosynthetic cells.

Vision and brains

Every creature casts vision rays and feeds them to its own neural network, which drives the thrusters.

The world is a tiled light map with nutrients on the ground. The simulation scales to large populations (the tutorial quotes up to 200,000 creatures, which needs a fast machine and at least 4 GB of RAM in the browser).

Screens

The whole world zoomed out: light pools, and producers, grazers and predators as coloured dots A selected creature: its 13×13 body grid, cell legend, and the role buffs and debuffs that v1 used Species diversity analysis: species clustered by body plan and placed by feeding strategy

What v2/v3 changed

v1 gave each feeding role fixed bonuses and penalties (the “buffs and debuffs” in the inspector). The rewrite removed them: every cell has the same physical rules for everyone, energy is strictly conserved, and the food chain, weather and climate do the selecting. See the current version for details and the live world.