UE5 and Houdini lightning

I've been working on a lightning effect/attack! I used #UE5 and #Houdini, here is the breakdown on how to generate the meshes, render them in unreal, and also make them movable without a rig!

Mesh generation

First I used Houdini to generate a mesh containing all the lightning bolts I needed.

Mesh generation

To do so, I have a network that starts with a line, distorts it with two layers of noise mixed together, but weighting those noises so that it distorts 100% of the center and 0% of the tips. This is because I want to make an attack that starts at one point and ends at another.

Mesh generation - data

To render the lightning in UE5 we need more information on the mesh, we could store this in the UVs or in the vertex color, but for the sake of visualization, I’ll do it with the vertex color.

Mesh generation - data

We need to encode two things:

First, a “Bolt Id” that differentiates each bolt from each other, to be able to iterate over them, I equally distributed all of them from 0 to 1

Mesh generation - data

Then another one that tells us in which direction the bolt will travel, if it is always from top to bottom you could assume this information, but having it rendered gives more flexibility

UE5 - Rendering

With this ready, we can start rendering the mesh in #UE5.

The first part of the effect is rendering only a few bolts at a time, the key here is to step our “Bolt Id” with time (modulated to 1) to get a mask like this one:

UE5 - Rendering

And then if we combine this mask with other one with a little offset we can mask only the bolts that fall in between, like this:

UE5 - Rendering

This is the logic inside the material:

UE5 - Rendering

Then to light them, I went with having two colors that will be flickering, using the same module masks we used for masking, but without stepping, with this, we can lerp between colors and give variety.

UE5 - Rendering

With this we are already rendering a flickering light bolt, we are only missing deformation. But before we move on I added a flickering light that moves at the same rate as the bolts and changes color the same way to make it blend in a bit more.

UE5 - Bending

Since this is an attack and I only need to adjust the tips to make full contact, with a simple displacement we can fake the effect, rotation will not be perfect if deformed to much but this will never be the case.

So the logic behind the deformation is using the “up” gradient to lerp between two positions, the start and the end, as simple as that.

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