Unreal Key
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Unreal Key

Render a Unreal Key for Smode to use as Alpha Layer

It’s important to that the name of the node contain Smodevfx and not front or back
The key need a Unreal Color Viewport Render a Unreal Color Viewport for Smode to use as Back and/or Front Read More setup, Once you have the color viewport you can create the second viewport
Choose one key type and then do the Texture replacement (see later in this doc for how to do the Texture replacement)

Key type

With Depth

In the Smode Rig you can enable the Use Depth checkbox, this will fill the FrontDepth texture
To control the depth value you can do this via the Smode rig in Smode ( changing the setting property count to advanced )

With Depth and DOF

Like the depth you can just put a render target in the SmodeRig and then use that as the texture replacement of the second viewport
Using the depth with the DOF will impact more the performance that just using the depth because we apply the DOF effect to the depth

With Custom Stencil

Enable custom stencil in the project setting
In your object enable render custom depth pass and set the stencil value to 255
In the Smode Rig you can enable the Use Stencil checkbox, this will fill the FrontStencil texture

With Custom Stencil and DOF

Like the custom stencil you can just enable the Use Stencil and Use Blurred Stencil checkbox in the SmodeRig and then use the FrontDOFStencil as the texture replacement of the second viewport
Using the Custom Stencil with the DOF will impact more the performance than just using the stencil because we apply the DOF effect to the stencil

Rendering only specific Object and using the Alpha

This method can be used when using multiple node to render a Back and a Front, or when only doing front
by calling the first viewport of your node front you can use the Front Actor list and/or Front actor Layers to make a selection of object that will be rendered in this front viewport

With that you can use the Front alpha render target as a texture replacement

Texture replacement

The render target that you chose in the SmodeRig need to be used as a texture replacement of a second viewport in your nDisplay node like that: This second viewport need to have a projection policy type set to Manual It can be placed below the first viewport ( this matching your mosaic made in the NVIDIA control panel )
Do not forget to put Smodevfx in the name of the node for the texture copy to be active

Nvidia Mosaic

When doing a Key you need to setup a Mosaic inside the NVIDIA control panel ( generally 2 screen arranged vertically )
you can also use the https://www.nvidia.com/en-us/drivers/mosaic-utility/ and the command line like 
configureMosaic.exe set rows=2 cols=1 res=3840,2160,60

Limitations

There are, of course, limitations to the depth and stencil key techniques. Perhaps most apparent is that if this technique is used with either Temporal Anti-aliasing (TAA) or Temporal Super Resolution (TSR), then the edges of our mask will jitter slightly as the temporal jittering shifts the screen around ever so slightly.
The other limitation is that this techniques won't work on translucent materials, since those are rendered to a separate gbuffer. If you were to try this techniques with the Separate Translucency scene texture, you'll end up bringing forward all of the accumulated translucency within the bounds of your selected primitive, which may not be desirable.
Becarefull if you have multiple GPU in your server because Unreal may try to run the different viewport on different GPU, even on integratedGPU of the CPU

See Also: