Katmai Tidal Rave

Living on the coast, as the wolves in our upcoming Katmai game expansion do, means that the ocean is very important. It's the source of most of the food that these wolves eat. And that means that the ocean is an important element in the game -- much more important than creeks and rivers and lakes have been in the game. So we are using a new water system in the Katmai expansion, called Crest. It's much more powerful and sophisticated than the water shader, Lux, that we've been using in the game so far. (And it's more graphically demanding, so lower graphics quality levels will continue to use Lux.)

Wolves don't care how the ocean looks, but they do care about how it works -- specifically, the tide cycle. Our Katmai science advisor Ellen Dymit says that Katmai wolves know when a low tide is coming. Why do they care? Because low tide offers their best access to prey. For example, during the salmon runs, in the lower stretches of the rivers, the salmon swim faster when the tide is rising and slower when the tide is going out, due to the push or pull of the water. So that makes a difference in your fishing success rate! Furthermore, seals and sea otters haul out to rest on coastal rocks. Some of those rocks are just offshore, so you have to swim to get to them -- except at low tide! Then you can walk right out there, which makes it easier to get close enough for a good attack.

So we needed to create a tide system. Raul tackled this along with other integrations of the water system into the game. But further complicating this feature is that all the NPC animals need to know about the tides, so they can act appropriately when on the shore. This was a problem because we designed the game originally with the idea that the environment is fixed, at least within each season. We generate a navigation grid, a navgrid, that contains detailed navigation and pathfinding data for NPC animals -- where the topography is easy, where it's navigable but difficult, and where it is impassible. And where, of course, there are water bodies. All this data gets baked into a data file, and that means that each animal doesn't need to "read" the environment around them, which can get quite heavy on performance. Instead they just read the data in the navgrid, which has distilled it down nicely for them. This works well and let's us have seasonal variations, like the flooding in Slough Creek in the month of May. But it does not support hourly changes to the water levels.

So Tommi had to dive in and design a tide subsystem for the navgrid system. It wasn't technically feasible to have a truly continuous movement of the ocean, so we ended up with six tide levels: Spring low and high tides, average low and high, and neap low and high. When the tide is flooding or ebbing, the ocean water moves from one to another, then stays at each intermediate level for a few game-hours. You can think of them as quantum levels, with the ocean moving rapidly from one to the next, instead of continuous movement from low to high tide. It's a compromise but I think it captures the essential features of tides within the constraints of our game framework.

So tides are one of a number of all-new features that are coming to the Katmai Coast game expansion. We've still got lots of work to do on it, so stay tuned to learn more in upcoming devblogs!