Getting started with ray tracing

The High Definition Render Pipeline (HDRP) includes preview ray tracing support from Unity 2019.3. Ray tracing allows you to access data that's not on screen. For example, you can use it to request position data, normal data, or lighting data, and then use this data to compute quantities that are hard to approximate using classic rasterization techniques.

This document covers:

Hardware requirements

Full ray tracing hardware acceleration is available on the following GPUs:

  • NVIDIA GeForce 20 series:
    • RTX 2060
    • RTX 2060 Super
    • RTX 2070
    • RTX 2070 Super
    • RTX 2080
    • RTX 2080 Super
    • RTX 2080 Ti
    • NVIDIA TITAN RTX
  • NVIDIA GeForce 30 series:
    • RTX 3060
    • RTX 3060Ti
    • RTX 3070
    • RTX 3080
    • RTX 3090
  • NVIDIA Quadro:
    • RTX 3000 (laptop only)
    • RTX 4000
    • RTX 5000
    • RTX 6000
    • RTX 8000
  • AMD RX series:
    • RX 6600
    • RX 6600 XT
    • RX 6700
    • RX 6700 XT
    • RX 6800
    • RX 6800 XT
    • RX 6900 XT
  • AMD Radeon Pro series:
    • Pro W6600
    • Pro W6800

NVIDIA also provides a ray tracing fallback for some previous generation graphics cards:

  • NVIDIA GeForce GTX
    • Turing generation: GTX 1660 Super, GTX 1660 Ti
    • Pascal generation: GTX 1060 6GB, GTX 1070, GTX 1080, GTX 1080 Ti
  • NVIDIA TITAN V
  • NVIDIA Quadro: P4000, P5000, P6000, V100

If your computer has one of these graphics cards, it can run ray tracing in Unity.

Before you open Unity, make sure to update your NVIDIA drivers to the latest version, and make sure your Windows version is at least 1809.

Ray tracing is also supported on specific console platforms. Consult console-specific documentation for more information.

You can use the Boolean SystemInfo.supportsRayTracing to check if the current system supports ray tracing. This function checks the operating system, GPU, graphics driver and API.

Integrating ray tracing into your HDRP Project

Before you use ray tracing features in your HDRP Project, you need to set up your HDRP Project for ray tracing support. HDRP only supports ray tracing using the DirectX 12 API, so ray tracing only works in the Unity Editor or the Windows Unity Player when they render with DirectX 12. You need to change the default graphics API of your HDRP project from DirectX 11 to DirectX 12.

There are two ways to do this:

Once you have completed one of these, move onto Final setup.

Render Pipeline Wizard setup

You can use the Render Pipeline Wizard to set up ray tracing in your HDRP Project.

  1. To open the HDRP Wizard, go to Window > Render pipeline > HD Render Pipeline Wizard.

  2. Select the HDRP + DXR tab.

  3. Click the Fix All button.

To enable ray tracing for specific effects, enable the ray tracing features in the HDRP Asset.

For information on how to set up ray tracing for your Scene, see final setup.

Manual setup

To set up ray tracing manually, you need to:

  1. Make your HDRP project use DirectX 12.
  2. Disable static batching on your HDRP project.
  3. Enable and configure ray tracing in your HDRP Asset.
  4. Ensure ray tracing resources are properly assigned.
  5. (Optional) Enable ray-traced effects in your HDRP Asset.

Upgrading to DirectX 12

HDRP enables DirextX12 by default. To enable DirectX 12 manually:

  1. Open the Project Settings window (menu: Edit > Project Settings), then select the Player tab.
  2. Select the Other Settings drop-down, and in the Rendering section, disable Auto Graphics API for Windows. This exposes the Graphics APIs for Windows section.
  3. In the Graphics APIs for Windows section, click the plus (+) button and select Direct3d12.
  4. Unity uses Direct3d11 by default. To make Unity use Direct3d12, move Direct3d12 (Experimental) to the top of the list.
  5. To apply the changes, you may need to restart the Unity Editor. If a window prompt appears telling you to restart the Editor, click Restart Editor in the window.

The Unity Editor window should now include the <DX12> tag in the title bar:

Disabling static batching

Next, you need to disable static batching, because HDRP doesn't support this feature with ray tracing in Play Mode. To do this:

  1. Open the Project Settings window (menu: Edit > Project Settings), then select the Player tab.
  2. Select the Other Settings drop-down, then in the Rendering section, disable Static Batching.

HDRP Asset configuration

Now that Unity is running in DirectX 12, and you have disabled static batching, enable and configure ray tracing in your HDRP Asset. The previous steps configured Unity to support ray tracing; the following step enables it in your HDRP Unity Project.

  1. Click on your HDRP Asset in the Project window to view it in the Inspector.
  2. In the Rendering section, enable Realtime Ray Tracing. This triggers a recompilation, which makes ray tracing available in your HDRP Project.

Ray tracing resources

To verify that HDRP has assigned ray tracing resources:

  1. Open the Project Settings window (menu: Edit > Project Settings), then select the HDRP Default Settings tab.
  2. Find the Render Pipeline Resources field and make sure there is a Render Pipeline Resources Asset assigned to it.

(Optional) Enable ray-traced effects in your HDRP Asset

HDRP uses ray tracing to replace certain rasterized effects. To use a ray tracing effect in your Project, you must first enable the rasterized version of the effect. The four effects that require you to modify your HDRP Asset are:

  • Screen Space Shadows
  • Screen Space Reflections
  • Transparent Screen Space Reflections
  • Screen Space Global Illumination

To enable the above effects in your HDRP Unity Project:

  1. Click on your HDRP Asset in the Project window to view it in the Inspector.
  2. Go to Lighting > Reflections and enable Screen Space Reflection.
  3. After enabling Screen Space Reflections, go to Lighting > Reflections and enable Transparent Screen Space Reflection.
  4. Go to Lighting > Shadows and enable Screen Space Shadows.
  5. Go to Lighting > Lighting and enable Screen Space Global Illumination.

Your HDRP Project now fully supports ray tracing. For information on how to set up ray tracing for your Scene, see final setup.

Final setup

Now that your HDRP Project supports ray tracing, there are steps you must complete to use it in your Scene.

  1. Frame Settings validation
  2. Build settings validation
  3. Scene validation

Frame Settings

To make HDRP calculate ray tracing effects for Cameras in your Scene, make sure your Cameras use Frame Settings that have ray tracing enabled. You can enable ray tracing for all Cameras by default, or you can enable ray tracing for specific Cameras in your Scene.

To enable ray tracing by default:

  1. Open the Project Settings window (menu: Edit > Project Settings), then select the HDRP Default Settings tab.
  2. Select Camera from the Default Frame Settings For drop-down.
  3. In the Rendering section, enable Ray Tracing.

To enable ray tracing for a specific Camera:

  1. Click on the Camera in the Scene or Hierarchy to view it in the Inspector.
  2. In the General section, enable Custom Frame Settings. This exposes Frame Settings just for this Camera.
  3. in the Rendering section, enable Ray Tracing.

Build settings

To build your Project to a Unity Player, ray tracing requires that the build uses 64 bits architecture. To set your build to use 64 bits architecture:

  1. Open the Build Settings window (menu: File > Build Settings).
  2. From the Architecture drop-down, select x86_64.

Scene validation

To check whether it's possible to use ray tracing in a Scene, HDRP includes a menu option that validates each GameObject in the Scene. If you don't setup GameObjects correctly, this process throws warnings in the Console window. For the list of things this option checks for, see Menu items. To use it:

  1. Click Edit > Render Pipeline > HD Render Pipeline > Check Scene Content for Ray Tracing.
  2. In the Console window (menu: Window > General > Console), check if there are any warnings.

Ray tracing effects overview

HDRP uses ray tracing to replace some of its screen space effects, shadowing techniques, and Mesh rendering techniques:

Ray tracing and Meshes

HDRP changes how it handles Meshes in your scene when you integrate a ray traced effect into your project.

When you enable ray tracing, HDRP automatically creates a ray tracing acceleration structure. This structure allows Unity to calculate ray tracing for Meshes in your scene efficiently in real time.

As a result, ray tracing can change how some Meshes appear in your scene in the following ways:

  • If your Mesh has a Material assigned that doesn't have the HDRenderPipeline tag, HDRP doesn't add it to the acceleration structure and doesn't apply any ray traced effects to the mesh as a result.
  • If your Mesh has a Decal Material assigned, HDRP doesn't add it to the acceleration structure and the Mesh doesn't appear in your scene.
  • If a Mesh has a combination of Materials that are single and double-sided, HDRP flags all Materials you have assigned to this mesh as double-sided.

Ray tracing light culling

Ray tracing requires HDRP to cull lights differently to how it culls lights for rasterization. With rasterization, only lights that affect the current frustum matter. Since ray tracing uses off-screen data for effects such as reflection, HDRP needs to consider lights that affect off screen geometry. For this reason, HDRP defines a range around the camera where it gathers light. To control this range, use the Light Cluster Volume override. It's important to set a range that accurately represents the environment scale. A higher range makes HDRP include lights further away, but it also increases the resource intensity of light culling for ray tracing.

Ray tracing mode

HDRP includes two ray tracing modes that define how it evaluates certain ray-traced effects. The modes are:

  • Performance: This mode targets real-time applications. If you select this mode, ray-traced effects include presets that you can change to balance performance with quality.
  • Quality: This mode targets technical demos and applications that want the best quality results.

HDRP exposes different properties for some ray-traced effects based on the ray tracing mode you use..

You can change which ray tracing mode HDRP uses on either a Project level or effect level. To change the ray tracing mode for your entire Project:

  1. Click on your HDRP Asset in the Project window to view it in the Inspector.
  2. In the Rendering section, enable the Realtime Raytracing checkbox, open the Supported Ray Tracing Mode drop-down and select a ray tracing mode from open.

If you select the Both option, you can change the ray tracing mode for each ray-traced effect. To do this:

  1. In the Scene or Hierarchy view, select a GameObject that contains a Volume component that includes a ray-traced effect.
  2. In the Inspector for the ray-traced effect, change the Mode property to use the ray tracing mode you want the effect to use. This changes the properties available in the Inspector.

Ray tracing project

You can find a ray tracing project that contains all the effects mentioned above in the Small Office Ray Tracing sample project. This Project is already set up with ray tracing support.

Limitations

This section contains information on the limitations of HDRP's ray tracing implementation. Mainly, this is a list of features that HDRP supports in its rasterized render pipeline, but not in its ray-traced render pipeline.

Unsupported features of ray tracing

There is no support for ray tracing on platforms other than DX12 for now.

HDRP ray tracing in Unity has the following limitations:

  • Doesn't support vertex animation.
  • Doesn't support decals.
  • Doesn't support Box-shaped spot lights.
  • Doesn't support the volumetric part of the fog.
  • Doesn't support tessellation.
  • Doesn't support per pixel displacement (parallax occlusion mapping, height map, depth offset).
  • Doesn't support VFX and Terrain.
  • Doesn't have accurate culling for shadows, you may experience missing shadows in the ray traced effects.
  • Doesn't support MSAA.
  • Doesn't support Graphics.DrawMesh.
  • Ray tracing isn't supported when rendering Reflection Probes.
  • HDRP doesn't support orthographic projection. If you enable orthographic projection mode, you might experience rendering problems for Transparent Materials, volumetrics and planar reflections.
  • Ray Traced and Screen Space effects won't appear recursively in Ray Traced Reflections, Ray Traced Global Illumination or Recursive Ray Tracing. This means, for example, you won't be able to see Screen Space Global Illumination in ray-traced reflection.

Unsupported shader graph nodes for ray tracing

When building your custom shaders using shader graph, some nodes are incompatible with ray tracing. You need either to avoid using them or provide an alternative behavior using the ray tracing shader node. Here is the list of the incompatible nodes:

  • DDX, DDY and DDXY nodes, and NormalFromHeight nodes.
  • All the nodes under Inputs > Geometry (Position, View Direction, Normal, etc.) in View Space mode. Furthermore, Shader Graphs that use Custom Interpolators aren't supported in ray tracing.

Unsupported features of path tracing

For information about unsupported features of path tracing, see Path tracing limitations.