Simulate!

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Real Loop Nodes!

Today we're going to mess with deadly experimental Blender.

Let's get right to it: there's an alpha build of Blender available that includes 2 new Geometry Nodes.

• Simulation Input

• Simulation Output

These nodes are astonishingly powerful.

First, grab the build here (the one called 'geometry-nodes-simulation' at the bottom of the list):

Open it up, switch to the Geometry Nodes tab, select the cube, and hit New to add a new Geometry Nodes modifier. (It does say "use at your own risk," so don't use this on a real production or anything, it's still a bit crash-prone and possibly buggy. Make sure to save your file every few minutes!)

Now, add 2 nodes between the Input and Output: a Simulation Input and a Simulation Output.

The Simulation Input node always needs to be connected to a Simulation Output node for anything to work. When you connect them, it creates a frame around both nodes.

Anything inside this frame is inside the loop.

The Geometry output from the Simulation Input node gives you the geometry from the last frame. Once it goes back into the Simulation Output, it is returned through the Simulation Input the next frame.

Here's a simple way to visualize it. Add a single node inside your loop: Set Position. Type 0.1 into the Z value of the Offset input.

Now hit play. Your cube should move slowly upward.

You've made your first loop! (Unless you've done this before, in which case it's your second.)

But why does it do that?

To start out, the cube geometry is passed into the loop.

Then it's offset on the Z by 0.1. Simple.

Then it goes into the Simulation Output, which sends it back to the Simulation Input.

Which spits it out into the loop again.

Then, it gets offset by 0.1, and goes into the Simulation Output again.

This happens continuously until you hit pause. (Hit SHIFT-LEFT ARROW to return to frame 1 and reset the simulation. You might have to hit play and pause and go back to frame 1 again to get it reset all the way.)

Here's an ugly blurry diagram to help explain that:

What else can you do?

A lot of stuff. I used a Join Geometry node and joined in new geometry every frame to create a shooting-star-trail effect. (be careful with this—you could end up creating a lot of geometry really fast!)

There's no room for another screenshot—check out the short video below to learn how to make it!

Tutorials

I couldn't find any easy tutorials explaining this stuff—so I made one. It'll help you understand the loop (if not, you'll make something cool anyway. The screenshot at the top is from this technique.)

This one by Kuldeep Singh is cool but a bit advanced (he rebuilds Blender's entire Particle System from scratch using nodes):

News

• Blender 3.4 should be coming out on December 7

• If you enable Node Wrangler in Blender 3.4, you can SHIFT-CTRL-CLICK stuff in Geometry Nodes to preview it in the viewport—a total lifesaver

• Selecting & editing on Text objects is going to look a bit nicer

• There's also going to be a Distribute Points In Volume node—finally!

Thanks for reading, and have a great week!

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