Render 3D Tiles in Unreal Engine

[kring]

An Unreal Engine Plugin for rendering 3D Tiles Batched 3D Models (b3dm) will likely consist of two main parts:

• GltfMeshComponent: A UPrimitiveComponent-derived class representing a single tile / glTF model. It may be helpful to derive from UMeshComponent or UCustomMeshComponent, but even if not, looking at their source code will be helpful. We'll also need a corresponding FPrimitiveSceneProxy-derived class, GltfMeshSceneProxy. Graphics Programming Overview has a good explanation of UPrimitiveComponent and FPrimitiveSceneProxy. In short, the former represents the model on Unreal's game thread, while the latter represents it on Unreal's rendering thread.
• Cesium3DTilesetActor: An Actor class that represents the entire tileset. Its Tick method can be used to select appropriate tiles each frame and create/destroy the primitives above as needed.

With these pieces in place, it should be simple for users to add a 3D Tiles tileset to the world using the Unreal Editor.

We may need to implement most of the code that loads a glTF file and creates Unreal Engine resources from it. While Unreal Engine has a built-in glTF importer plugin, this is meant to be used at design time rather than runtime. It converts the glTF to another form rather than creating a renderable resource directly. For 3D Tiles rendering, we need to be able to load glTFs dynamically. Depending on the license, we may be able to borrow parts of the glTF Importer or the third-party glTF for UE4 plugin, though. The Unreal Engine source code is installed with Unreal Engine and is very easy to explore with Visual Studio.

Rumor has it there is a "glTF runtime translator" coming in Unreal Engine 4.25 that will obviate the need for us to develop our own glTF support.

Useful Resources

• Unreal Engine programming in C++
• Graphics Programming Overview
• Creating Plugins

[kring]

Notes on this from the call with Sebastien, Johan, and Alban from Epic today:

• Unreal Engine 4.25 will have a feature to load any DataSmith-supported format (including glTF) at runtime, and then convert it to Unreal assets/actors. Should just take 2-5 lines of code.
• Johan points out this wasn't designed for our use-case - rapid loading and unloading of assets at runtime - but it might be ok, we should try it.
• We can try it today by downloading the 4.25 preview release from Github (and possibly also from the Epic store?)
• If we have any questions (about this or in general), we should post to the Unreal Developer Network but also let Seb and Alban know that we did.

[kring]

Closing in favor of more specific issues.