Canadian engineers are brilliant,
they've developed a sort of paint that actually floats above the roadway.
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I don't think it's a bubble... too much coverage beyond the vehicle scope.
I wanted to see how large the 'bubble' of particles around the car is and, in photomode at least, it doesn't even feel like a bubble as it covers the whole area you can look at with the camera. With heavy snow (easier to see) there must be an untold amount of particles on screen at once, no idea how many but it must be in the hundreds of thousands.
I should have said "bubble around the
camera," not "car." Games that use particle-based techniques and allow free out-of-character camera motion generally use distance-based particle culling (Halo Reach is the same way, if you fly through the city in paused replay mode you'll see particles everywhere, but they only exist in a bubble around the camera, as the game's particle system tops out at a few tens of thousands of simultaneous particles.). The "radius" of particle existence is pretty substantial for this sort of system, though.
Anyway, I figured I'd investigate this a bit by checking out heavy snow in Norway.
A quick look at photomode snow tells me that although the bubble is pretty big, the snow particles definitely pop in as you move around. I tried a rough count of how many particles were in view when looking at a lit sky in photomode at minimal FoV (which I very roughly guestimated at 23.6 degrees), and it was something around 4000 (I counted a 1/8th segment and extrapolated). Now, if we imagine that the density is the same all around us and that the bubble is spherical, this implies somewhere in the vague ballpark of 600,000 particles that could (i.e. ignoring geometric obstruction) be visible if we made a full 360-degree render covering the entire possible visual sphere.
As to the particles themselves? They're fairly simply; basic trajectories, seemingly non-interactive*. I noticed that particles that have been distance-culled are remembered when you come back in range, which makes me wonder if they're not randomly generated during camera movement but procedurally determined by a time-based seed.
*One of the snowflakes in
this shot is actually
inside the car