FAQ

Questions, answered.

Requirements, Patreon, license keys and updates. Anything else, ask.

The basics

What is Harlow?

Harlow is a plugin for TouchDesigner. It adds a real-time GPU path tracer and GPU solvers for liquids, fire and smoke, rigid and soft bodies, fracture and surface weathering, as nine custom operators (POPs and TOPs). See the overview.

What do I need to run it?
  • Windows
  • An NVIDIA RTX 30-series GPU or newer, with driver R590 or newer
  • TouchDesigner 2025.30000 or later

An older card or driver makes the HRLW Path Tracer TOP show an error saying which. There is no macOS or AMD version, because Harlow is built on NVIDIA OptiX and CUDA.

Do I need to rebuild my projects?

No. Harlow operators sit inside ordinary networks. You feed them POPs, they read your Camera, Light and Environment operators, and the Path Tracer outputs a TOP like any other. How it fits.

How do I install it?

Close TouchDesigner, copy the Harlow files into Documents/Derivative/Plugins/Harlow, and start it again. The operators appear in the OP Create dialog among the custom operators. The full steps are in Install & activate.

Patreon and licensing

How do I get Harlow?

Join the Harlow tier on Patreon. Each build is posted there, and you get license keys from the license page by logging in with Patreon.

What happens if I cancel?

You keep every build released while you were subscribed, and they keep working forever. Newer builds need an active membership.

How many computers can I use?

Up to 3 at a time. You can remove a computer on the license page to make room for a new one, a few times a year.

Does Harlow need the internet?

Only to get a key. After that it checks the key offline, with no phoning home. For a computer that's never online, open the license page on your phone and type in the machine code that Harlow shows.

I reinstalled Windows or got a new computer.

The machine code changes when Windows is reinstalled. Remove the old computer on the license page and activate the new one.

Does a gifted membership work?

Yes. A gifted membership gets keys while the gift lasts. Free trials don't include keys.

Can I share Harlow or my project files?

The plugin files are for you only and may not be shared. Your .toe files are yours to share: the key is stored on your computer, not in the project, so anyone opening it needs their own license to run the Harlow operators.

Using it

Why is the Path Tracer black after an update?

On the first start after an update the renderer compiles in the background, which takes a minute or two the first time. The TOP shows a warning until it's ready, and TouchDesigner stays responsive.

Why is the image noisy when things move?

That's how path tracing works: the image gets cleaner while the camera is still and restarts or reprojects when things move. The DLSS-RR denoiser and the quality presets keep it clean at frame rate. See Path Tracer.

Can I use the simulations without the Path Tracer?

Yes. With Output to TouchDesigner on, the Liquid, Bodies and Fracture POPs hand TouchDesigner regular POPs and the Volume Solver hands it 3D textures, so you can render or process them with any other operator.

Something isn't working.

Check Troubleshooting first. If that doesn't help, get in touch with your GPU, driver and TouchDesigner version.