la gpu lightmass e' stata implementata nella versione 4.26:
GPU Lightmass. Lightmass is getting an upgrade using a progressive lightmapper that works on the GPU. It supports full material representation, taking into account some things ignored by Lightmass, such as Vertex Colors. GPU Lightmass is based on ray tracing technology, which currently requires Windows and a DXR capable card supported by NVIDIA. As other vendors support ray tracing, UE4 will not be tied to a specific operating system or graphics card.
To enable GPU Lightmass:
Enable Ray Tracing and set the Default RHI to DX12 in the Project Settings. (Requires a DXR capable graphics card with Windows 10 build 1809 or later.)
Enable Virtual Texture Lightmaps project setting for real-time preview in the editor.
Enable the GPU Lightmass plugin.
GPU Lightmass is now available through the Build menu.
You can also use the r.GPULightmass.* console commands to adjust GPULightmass settings and ToggleLightmapPreview command to start GPU Lightmass in the editor.
GPULightmass throttles itself when Realtime is enabled in the Level Editor viewport.
Recommended to set r.RayTracing.ForceAllRayTracingEffects 0 in the editor to disable all ray tracing effects. This helps give more resources to GPULightmass and avoids some confusion between features, such as ray tracing soft shadows rendering on top of lightmaps.