Viewer Engines

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The views expressed below are not necessarily those of the Open Metaverse Research Group, but are the author's alone.

Part of minimizing the simulation lag is to minimize the work the server has to do, pushing data instead to the viewer to render. Examples of this in SL and Opensim are the particle system and non-physical scripted movement like llTargetOmega.

The current versions of SL and Opensim object editors limit the user to using diffuse, normals, and specular textures for a very basic PBR, however this is not a limit of the servers, this is a viewer based limitation. The current Linden Lab project to implement use of *.gltf as a valid mesh upload format will be accompanied by a wider range of PBR materials textures that can be applied to each mesh material to provide a wider range of optical properties to rendering, which will enable creators to build more photorealistic content.

Expanding PBR Abilities

*.gltf file formats are associated with the proprietary Unity *.fbx and the binary *.glb formats that are all compatible with Unity Hub and Unity Core, as well as Blender and other 3d modeling applications, and virtual world and game platforms from DCL to Sandbox to the Steam ecosystem etc. This will empower users to bring in Unity assets to SL and Opensim more easily while retaining PBR features. This capability is in the pipeline for the standard SL viewer and their open source third party offshoots like Firestorm that is useful in SL and Opensim.

Unity-Based SL/OS Viewer

There is a new SL viewer in development called Crystal that is Unity based. We assume its code will be enabled for Opensim as well directly or as an alternate release. The fact that a Unity-based viewer can already interact with the basic SL server system demonstrates how the server system does a lot less unique work than most people imagine.

Unreal Engine 5.1

This leads one to consider the possibility that more advanced game engines can be used as the core of other alternate viewers, such as Unreal Engine 5.1, which is now considered the cutting edge of game engines. This would enable Opensim to leapfrog over a decade of game engine development. We look forward to seeing teams organize around creating an Unreal Opensim Viewer.

The advantage of leapfrogging to using Unreal is that it is open source, while Unity is not. The Unreal engine code is available on github, there are royalty arrangements for commercial use, and developers can contribute code back to Unreal for ongoing improvement. This makes it a superior choice for an Open Metaverse over Unity.

An Unreal Opensim Viewer developer would use a Standard license unless they plan to sell their viewer.

Standard license

For creators and publishers who don’t require premium support or custom terms. Also suitable for students and educators.


  • Free to download and free to use in many cases.
  • See the FAQ for when royalties apply.


  • All Unreal Engine features
  • Entire Quixel Megascans library
  • All learning materials
  • Community-based support

Advantages of Unreal Engine:

Niagara VFX Effects: A major change for particles, physics and other visual effects. Whether the physics