Move your mouse around and see the firefly follow it ! Press space to show the Number of Particles slider, which lets you choose the number of fireflies to be shown. When the slider is visible, you can press the up and down arrows the change the number of fireflies by +1 (resp. -1). If it lags, try having less particles. You can also try https://sulfurous.aau.at/#262838802
No firefly actually knows the position of the mouse. They just follow another firefly. The thing is, each frame each firefly chooses another firefly at random, and if the new firefly is closer to the mouse pointer than the ancient one, it becomes the new firefly being followed. This way, the fireflies globally approach the mouse pointer, without ever knowing its position (though they know whether a given firefly is closer to it than another one).
