Nvidia recently released a technical demonstration called the RTX Bonsai demo, showcasing advanced AI and ray tracing technologies running on a specialized Nvidia branch of Unreal Engine 5.6.1. This demo highlights several cutting-edge features such as DLSS multiframe generation, transformer models, ray reconstruction, and notably, RTX Mega Geometry path tracing with Nanite meshes. Unlike current Unreal Engine 5 games that use lower fidelity geometry for hardware Lumen ray tracing, this demo leverages RTX Mega Geometry to maintain high geometric detail in ray tracing, resulting in significantly improved reflections, shadows, and lighting fidelity.
The demo features impressive visuals including pixel-perfect direct shadows, mirror reflections with detailed indirect lighting, and rare effects like colored and transparent shadows where light passes through stained glass. It dynamically adjusts geometric detail using Nanite as the camera moves, maintaining a high level of detail in the ray tracing acceleration structures without the need to rebuild the entire BVH hierarchy constantly. This represents a major technical advancement in how geometry is handled in real-time ray traced scenes, enabling much more complex and realistic lighting effects.
A side-by-side comparison in the demo shows the difference between RTX Mega Geometry being off and on. With it off, reflections and shadows appear blocky, incomplete, or missing due to the use of lower resolution geometry for ray tracing. When turned on, the scene displays a much higher polygon count in the ray tracing view, resulting in far more accurate lighting and reflections. However, this level of detail comes at a performance cost, with the demo running just above 60fps at 4K DLSS performance mode on an RTX 5090, illustrating that such advanced ray tracing is still demanding even on top-end hardware.
The discussion also touched on the logistics for developers using Nvidia’s Unreal Engine branch. Transitioning to this branch should not be overly disruptive if developers are already using a recent Unreal Engine version, as the Nvidia features are added as supplementary options rather than replacing core systems. However, art assets designed around traditional Lumen or shadow mapping systems might require adjustments. This Nvidia branch represents a significant step forward, potentially paving the way toward Unreal Engine 6 capabilities.
Finally, an additional Unreal Engine update was mentioned, unrelated to the demo but relevant to the broader ecosystem. Epic is introducing a lower-end, non-Lumen RTGI system based on radiance field probes aimed at mid-spec PCs and certain handheld consoles, likely the upcoming Switch 2. This new system targets better scalability for lower-end hardware by trading off some reflection quality and fine lighting detail for improved performance and temporal stability. Together with Nvidia’s high-end demo, these developments illustrate Unreal Engine 5’s expanding versatility across different hardware tiers.
