Reworking the water simulation

I've spent a lot of time reworking the water simulation. When Evolve generates a world, the rivers carve channels that follow the shape of the land. I've always wanted to be able to dig into one of those channels and bring water back to my base to irrigate crops.

I had a very basic version of that working for a while. After several rounds of changes to the terrain and water, it stopped working the way I wanted. I've gone back over how water runs down slopes, flows through ground you've dug and falls over drops.

The hardest part has been getting everyone playing to see the same thing. The server decides where the water goes and sends those changes to each player. Once the water has found its level, I need the simulation to go quiet. A settled pool should only need the server's attention again when something changes.

I tried digging a hole beside a river, then cut into the bank to let the water through. The river was higher than the hole, so it filled up and kept going over the edge. I built up the rim with more earth. That held the pool in place, and the water that had already spilt out slowly soaked away.

The reason I wanted this in the first place was to give myself more choice about where to build. With a steady supply and enough fall, I can run a trench a long way from the river and bring water to the crops.

Caves are one place where I've put in a specific rule. If I dig down and break into a cave, the water falls through the opening and seeps away on the cave floor. Letting a river fill the whole cave would give the server an awful lot of water to keep track of.

I'm fairly happy with where it's got to. It works well in most of the cases I've tried, though it's still one of the rougher systems in the game. I want to see how it holds up when more people are digging and moving water on the same map.