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Device Passthrough

Mixed Reality devices which support passthrough mode, such as Quest 2/Pro/3, can be used with Hololight Stream. To enable this mode, see the Client Settings Documentation on enabling passthrough.

How it Works

In passthrough mode, any objects in the scene with an alpha value of 0 will be treated as passthrough. This means that, regardless the color, objects or skyboxes with an alpha of 0 will not be displayed and replaced with the users surrounding.

In Unity standard render pipelines scenes, skyboxes with solid color and alpha 0 will be treated as passthrough, however for URP and HDRP scenes this will not always be the case. To enable passthrough in URP or HDRP, refer to the following sections.

Universal Render Pipeline

The following settings must be set to use URP with passthrough.

Setting Location Recommended Value
Terrain Holes Universal Render Pipeline Asset Disabled
HDR Universal Render Pipeline Asset Disabled
Post-processing Universal Renderer Data Disabled / Follow steps below
Intermediate Texture Universal Renderer Data Auto

Post-Processing Adaptation

The below steps explain how to adapt the post-processing data for alpha rendering and can be imported from the Hololight Stream Examples package via the package manager, see URPAlphaPassthrough sample. These steps have been carried out with Unity's Universal Render Pipeline package V12.1.8 and may differ based on the version.

  • Copy the UberPost shader to the assets, found at Packages/Universal RP/Shaders/PostProcessing.
  • In the copied shader, change the first line to Shader Hidden/Universal Render Pipeline/UberPostWithAlpha" and add below lines, outputing the alpha channel from the shader.

  • Copy the Post Process Data file to the assets, found at Packages/Universal RP/Runtime/Data.
  • Select the copied Post Process Data file and set the inspector to Debug, see below.

  • Expand the Shaders section and set the Uber Post PS to the copied UberPost shader.

  • Set the Post Process Data section of the default Universal Renderer, in the active Render Pipeline Settings specified in the Project Settings Graphic's and Quality Settings, to the copied Post Process Data file.

Example

  • Create a 3D URP Unity project (the rest of this section has been done with the 3D Sample Scene (URP) available in the Unity Hub).
  • Add the com.hololight.stream and com.hololight.stream.examples packages to the project via the package manager.
  • Follow the steps in Project Configuration.
  • Import the URPAlphaPassthrough sample from the Hololight Stream Examples package via the package manager.
  • Set the Assets\Settings\Universal Renderer files Post Processing Data section to URPPostProcessDataWithAlpha.

  • Disable the HDR checkbox within the Quality section of Assets\Settings\UniversalRP-HighQuality.

  • Right click the Scene section and click XR -> Convert Main Camera to XR Rig to use the scene with an XR device.
  • Go to XRRig -> Camera Offset -> Main Camera and, in the Rendering section, set:
    • Post-Processing to true
    • Anti-aliasing to No Anti-aliasing
    • Culling Mask to Default

  • Go to XRRig -> Camera Offset -> Main Camera and, in the Background section, set:
    • Background Type to Solid Color
    • Background to zero in R,G,B and A
  • Enter play mode and connect from the client.

High Definition Render Pipeline

By default, HDRP does not render alpha information. To enable this, follow the steps below. For more information, see Unity Documentation on HDRP and Alpha Channel.

  • Open the HDRP Asset in the Inspector window.
  • Go to Rendering > Color Buffer Format.
  • Select R16G16B16A16.

Troubleshooting

  • Ensure the passthrough setting has been enabled on the client device, see enabling passthrough.
  • Ensure both client and server are using the same color space, see colorspace.
  • Ensure the Main Camera's background is a solid color with Alpha value of zero.

Limitations

  • Currently, intermediate alpha values are not supported. Alpha float values will be rounded up, i.e. either 1 or 0.
  • Skybox's with a solid color other than black may cause color bleeding on the borders of the objects.