GPU Raytracing Collisions

Learn how to enable GPU Raytracing Collisions in Niagara.

In Unreal Engine, you can set up a particle system to collide with objects in the level using the Collision module.

In previous versions of Unreal Engine, when using a GPU emitter, you had several options in this module. Typically, most used the Depth Buffer option, which generates a simulation of the environment. This is a low-cost, but also low-accuracy solution. The shapes are not accurately portrayed, and if a particle goes off the screen it disappears immediately.

GPU Raytracing Collisions is an experimental option in the Collision module, so you can use hardware ray tracing on the GPU. No matter whether the emitter and its particles are on-screen or off, or hidden behind an object, the collision will use raytracing to calculate an accurate result.

GPU Ray Tracing Collisions

The calculation is asynchronous, so the Niagara collision will be one frame behind.

Adjust Your Project Settings

To use this feature, your project must be set to DirectX 12 and your GPU must have hardware ray tracing enabled. To turn on these options, follow these instructions:

  • Open Edit > Project Settings.

  • Search for rhi.

  • Adjust the Default RHI option to DirectX 12.

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Next, enable ray tracing, also in your Project Settings.

  • Search for ray tracing.

  • Enable the options Support Hardware Ray Tracing and Ray Traced Shadows.

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Set Up the Collision Module

In the Collision module, adjust the settings to use this experimental feature. Set the GPU Collision Type to GPU Ray Traces (Experimental).

The Trace Provider is set to Project Settings by default, which picks the best from an array of options. However, you can also manually set this to HW Ray Tracing.

Set Up A Fallback (Optional)

You can set up a fallback in case ray tracing is not available. To do this, open Edit > Project Settings.

In the Plugins > Niagara section of the settings, there is a setting called Async Gpu Trace DI. It has an array set up with two options in it, HW Ray Tracing and Global Signed Distance Fields. When your options are set up like this, the system will first try to use ray tracing, but if ray tracing is not available then it will fall back to use distance fields instead. These are the default settings.

You can add elements to the array or rearrange as needed. However, in most cases, the default settings will be sufficient.

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