Water cycle - rain, evaporation, rivers

Nothing quite that complicated, but having rain produce water voxels requires you to delete some unless you want to end up with Waterworld.

I mean keeping a fixed amount of water on the planet would be nifty, but just the feel alone would be nifty.

No, and if this suggestion would require one, that's not really feasible.

That doesn't stop it from being nifty, if possible, though.

I figure you could do something like the weather in SE1. It notionally happens globally, but it's only simulated around players.

Working with two or a few water "bodies" is not that difficult, but handling the movement of a large number of small "bodies" in the field is very challenging.

As for the visual effects of "rain", water flowing into the riverbed and rising river levels, it is easier and more efficient to simulate rain only visually (or only in close proximity to the player) and to deal with the other effects differently, e.g. as "hidden", invisible sources of water in the river system.

Further - the planets in the game are very small, the linear dimensions are about 1/10 - 1/100 of the real size (the areas and volumes are then thousandths and millionths of the real areas and volumes), but the dimensions of the rivers and their simulated flows are disproportionately large, much larger than they should be relative to the scale of the planet.

The reason is simple - our perception of the world. We don't perceive the size of the planet as a whole, we don't see it. But we do see a river on a local section of the world.

So we can make the planet smaller without disturbing the plausibility of our perception of the world, it simply doesn't matter if the game planet is 10000 or 1000 or a hundred kilometers across - it will still be "big enough" for the game. But if a real river is two hundred meters wide, it cannot be reduced to twenty or even two meters - it will cease to be "big enough" and the river will become a stream... and that already distorts the perception of the reality of the world. Strongly...

So the water in the river has to be treated differently - the water cycle can be visually simulated to look like in nature, but the main volume of water that simulates the actual behaviour of the water in the river has to "circulate" differently in the game world.

Of course - it is one big, I would say quite fundamental, problem. The world is voxel... How to make in a voxel world a "water source" so that players can't dig to it? So that they can't isolate it and leave it hanging in the air...

Or vice versa - build a "well" or "chimney" around the source and divert the water to the opposite end of the hills and create new river.

I'm 105% confident that by day three at the latest, someone will try to do it...

And there is no complication that will prevent the players from doing so - they will take it as a challenge to their abilities.

Translated with DeepL.com (free version)