World Machine Development News

3026 Erosion Improvements

The Erosion device has been upgraded in build 3026. As World Machine’s most popular device, all changes to erosion have to be a bit cautious; but I think you’ll enjoy what’s to come 🙂

Eroding into river channels

The ability to erode into river channels has been around for a while, but it really hasn’t worked the way you want, especially when “Geologic time enhancement” is enabled. This became increasingly obvious with the new automatic rivers in 3025; doing any kind of strong erosion would either sink the river deep underground or leave it hanging out over the terrain like in the first image below.

It took much longer than I expected to hit upon a good solution to this problem. But the default behavior is now way better:

No more hanging rivers 🙂

Light years better! The river now feels fully integrated into the terrain, without the odd “buried or hanging” effect in first first image.

However, in some cases.. when we do massive erosion after placing rivers… it’s still not enough. This made me think more about what we’re actually trying to achieve when eroding a world that already has rivers placed.

Achieving Equilibrium

For example, here’s an example world based that has had extreme erosion performed after placing rivers. At first glance it looks fine. But look closer…

A great amount of rock has been worn away. 3026 ensures that the terrain around the river is roughly preserved, and it is.. but that means that the river ends up running down the ridges of the terrain!This would be.. unusual in real life 🙂

One usually doesn’t see rivers running down a ridgeline (left side)…

Let’s back up. What’s causing this problem?

Our desire to fix the river paths to their existing location is what causes us this trouble. In reality of course, the water channels are the primary agent of terrain change, and down-wear in concert with the rest of the terrain. What we’re trying here with a fixed river location is not physically plausible.

The solution is : uplift.


The terrain around the river has slowly uplifted during erosion, maintaining the river’s location at the bottom of local valleys

You now have the option of slowly having the earth raise beneath the terrain undergoing erosion. This provides the forcing function we need to keep the rivers in their proper place at the valley floor.

I think you’ll find this to be quite useful!

Preserve Edges

Build 3026 also makes sure the “Preserve Edges” option is A) no longer broken 😉 and B) interacts well with uplift.

When enabled, map edges are effectively sediment sinks (just like if you specified a river/sink mask), and play well with uplift. This lets you carve into the terrain automatically as uplift happens:

Uplifted erosion without and with “Preserve Edges” set

What’s happening in the comparison above is that the edges are being forced to their initial values in the bottom image. This creates the elevation differences that erosion needs to continue working; in the top image, erosion has essentially reached an end-state, where all large structures have been worn away.

Mask Structure

Finally, a new useful control has been added to Erosion: Mask Structure. The wear/sediment/flow masks are incredibly useful for texturing, but getting a good look from them has been counter-intuitive in the past. This has been fixed, and you can now simply set the structure slider lets you control how detailed/smooth you want the mask information to be.

Sliding the Mask Structure from 0..1

Better Geological-time Enhancement

As a final short aside, this control has been made much more fluid/controllable/predictable in terms of results. Without going into all the details…. I think you’ll like it.

About that compatibility…

With all these changes, it’s worth talking about compatibility. Erosion is now versioned, which lets us both preserve old behavior and also simplify things a bit.

You’ve probably noticed that Erosion pre-3026 has a bunch of odd compatibility check-boxes. This is due to making small improvements over the years without the benefit of the device versioning system. In order to preserve the old behavior, there needed to be a checkbox. And then, sometimes there wasn’t one, leading to changes when you didn’t want them…

Now that versioning is in place, we can remove some of them:

Simplified Erosion dialog

The compatibility options have been distilled down to some of the essential ones. If you load an older world, you’ll see more of the old options appear.

That’s it for now! 3026 should be coming out very shortly for you to play with the changes; after a short bugfix interval it will then drop to release channel as well.

By Stephen

Founder of World Machine

3 replies on “3026 Erosion Improvements”

Hey Stephen thanks for the update and work on erosion! Just to clarify where do we go to to report bugs we found inside of world machine?

Hi Jan,

All of the builds in the ‘Alpine Lakes’ line have been available on the Dev Channel. As of 3028, they are now also available for the Release Channel and Basic Edition as well!

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