Yasno Games devlog

Water runs downhill

2026-10-24T00:00:00Z

Our last post ended with "the rivers went in this month." That evening we deleted them.

They had a flaw nothing we added could reach. The old generator routed water between points 525 tiles apart. It knew the ground's height at those points and nowhere else, so it assumed the ground ran straight from one to the next, and wherever a ridge stood between two points, the river went over it. In one stretch of the world we counted 20 places where a river climbed 16 metres or more.

We had spent nearly four weeks on it by then, each fix laid over the last: points moved onto the troughs between ridges, troughs published for the points to find, a rule for where two streams meet. Every fix moved the climbs somewhere else. By October 12 four layers of the generator existed only to make rivers, and the rivers still climbed. We took out all four, 4,295 lines, and started again from what a river has to do.

Rules first

We wrote the rules down before any code. A big river never climbs. A small stream may climb a little. A hollow fills to its lip and spills over, so lakes are welcome. And nothing gets checked by sampling the ground along a river's length, because the far view of the world can't pay for it.

Every generator we read that gets rivers right does it one of two ways. Some build the terrain from the rivers, and the ranges grow around the drainage. Others let a river own the ground under it, cutting it down to a bed that only ever falls. Our ranges already come from colliding plates, so our rivers had to own their ground.

Coarse to fine

The next day the world moved onto hex cells of seven sizes, each three times finer than the one above, from cells 729 tiles across down to single tiles. Water is routed at every size. The coarsest cells find the big rivers and cut their valleys. Each finer size takes the rivers handed down to it, lays them over its own ground, and finds the smaller streams between them.

On the left is the land around the haven, where new players start, on October 13: streams branching into rivers, each in a valley of its own. On the morning of the 14th it went into the game.

The water stood in the air. A river coming down a mountain hung over the slope as a staircase of blocks, and more than half the wet tiles round the haven held water above their own ground. Some of that was the generator and some was how the game draws a river stepping down from one tile to the next.

The drawing went first. A fall is now drawn only where the ground beyond the water is lower, and the afternoon before that rule held, the world went under walls of water.

Combs

Then the rivers ran straight. Each size hands its ground down to the next as flat sloping triangles, and water on a flat slope takes the one steepest way down, the same way for every stream on it. A hex grid makes it worse: a stream turns only where the ground beside it falls away faster than the ground ahead, and on a smooth flank nowhere does. A mountainside's streams came out as the teeth of a comb.

We tried roughening the ground, which changed nothing, and holding each river to the line the coarse cells drew for it, which made rivers climb again.

Then we lost the valleys. We had made where a river starts depend on how steep the ground is, and how hard it cuts on the rain its land gathers. The haven is dry, gently sloping country, and around it the share of ground any river had cut fell from 98% to none. That is the right-hand map above.

Rain was the wrong thing to read. Valleys are cut over thousands of years by floods, and a dry country's floods run as high for their land as a wet one's. A river now cuts by the land it drains, and rain decides only how wide its water runs today. Around the haven, 84% of the ground came back cut.

The comb was still there. A level handed its rivers down as heights at its own points, so any bend smaller than one of its cells was lost on the way down, and the finer river sat in the straight groove the coarser one left. Now a level hands down each river's course whole, and the next size bends it through the ground beside it, so a river picks up bends at every size. A stream that starts on a plain wanders toward whatever lies lower, so streams gather into trunks.

That is one valley in our world viewer, which draws the generator's tiles without the game's look: on October 22, then today.

Lakes

Lakes came last. A lake the coarse cells found in a wide basin used to vanish at the tiles, because no small cell could see the whole basin, and the lake dried to a flat disc.

So a lake is handed down like a river. The morning after that went in, this was waiting.

Where a finer valley crossed the lake's rim, the lake stood on at its old level, a wall of water over the river that should have drained it. By nine that morning each size was flooding every lake handed to it afresh from its own ground, and the water standing round the haven fell from 22,848 tiles to 5,773.

Now a stream coming down a wooded valley fills a few ponds on its way.

The rivers come from a generator: seeded code, no trained model, nothing drawn by hand. Claude writes that code with us, and we decide what a river should look like and throw out what isn't one.

Seven mountain ranges

2026-10-12T00:00:00Z

We're Yasno Games, and we're making an MMO on a hex grid: an open world you cross on foot, generated from a seed. The mountains in that picture are our seventh go at a mountain range. The first six are gone, but git keeps everything, so we went back through it to show you what they looked like.

There are two kinds of picture here. The top-down maps are drawn from each version's own height code: 20 km of its world, all in the same light, one colour for one height across all of them. Everything else is the game itself, this month's build unless the text says otherwise.

Noise, twice

The first ranges, in March 2024, were Perlin noise: a height for every tile, read off a smooth random field. Noise makes hills. It never makes a range, because a range has a direction, and noise has none.

In October 2025 the noise got regions, and mountain regions got cliffs stepped in strata.

That is the second one in the game in February 2026, the week before it went: every tile a hexagonal column, so a hill is a staircase of them.

Plates, then nothing

In February we started from tectonics. The world split into plates, each with its own base height, their edges warped so they curve, and a ridge raised where two plates push together.

What you get is terraces where one plate's height meets the next, and one ridge. Two days later we took the heights out and started modelling what lies under the crust: denser and lighter provinces, hotspots, heat spreading from them. Those were fields, and none of them was a height yet. For those weeks the world in the game was flat.

Placing the mountains

In March we stopped deriving mountains and placed them. A continent grew a spine of peak cones joined by ridgelines, and streams grew down from the ridges, carving ravines as they merged. Over the summer an erosion stack went on top: glacial cirques bitten into the shaded side of the high peaks, and slopes shaped convex at the crest and concave at the foot.

These are the tallest of the maps, up to 2.8 km, and they had a feel in the game we liked.

That is the view from the top of one, in the August build we rebuilt to film it: the cone falling away to the coast on every side.

From above you can see the problem. Each cone is a circle stamped on the plain, and where two cones meet there is a straight seam. A placed mountain does not know why it is there, so nothing around it agrees with it.

Letting them emerge

In September the plates came back as the source. Crust thickens where two plates push together, and the height follows from the thickness. The spine, the cirques and the slope shaping came out: about ten thousand lines of code, deleted in one commit.

Thickness gives you a swell. It gives you no ridges, and no valleys inside it.

Sheets

Two days later we rewrote the plates themselves, and that is the seventh range. Where one plate runs under another the crust stacks into sheets, the way real fold-and-thrust belts are built.

The plates were cells on a lattice, and the ranges followed the lattice: straight runs, 60° corners. The next day every plate edge started being read through a smooth warp, so coasts, fronts and ranges bend together and never at a corner.

Walkable

That version had a problem you could feel. Most of the ground was walkable, and the ridges, the part you came for, were almost all walls. A player climbs one level per tile, and the faces were steeper than that.

We could raise the step or lower the mountains. We lowered the mountains to the angle loose rock actually rests at, 34°, with scree running out about 150 tiles from the foot of each range. That is still too steep to walk straight up, so you climb across the face, the way you would a real scree slope. Ground at 45° or steeper fell from 2.4% of land to 0.75%, and what stayed that steep was mostly gorge walls, which is where you would expect a wall.

For scale: a tile is about 1.7 m across and a level is 0.8 m. The geology is Earth's, squeezed so a range fits in a world you cross on foot.

What didn't work this month

Ravines. We cut a gully down a range's flank every 46 tiles, 17 levels deep. In the game it was corrugated iron: a ridge every 80 metres, walking across it felt like waves, and the far view could not draw it. It came out the same day.

What did stay: a range's crest now rounds off as fast as its height wears down, trees thin out where the slope gets too steep to hold soil, old collisions inside a continent leave worn-down belts instead of nothing, and this month rivers started running along the troughs between ridges and crossing at the passes.

That is the range as it stands this month, its crest about 900 m above the sea.

Where it stands

It isn't done. Lakes have been tried three ways and taken out each time, because they cost more to generate than they showed. The rivers went in this month.

Every range here comes from a generator: seeded code, no trained model, nothing drawn by hand. Claude writes that code with us, and we decide what the mountains should be and throw away what isn't it, six times so far.