At GDC 2026, NVIDIA and CD Projekt RED showed a demo of the Polish studio’s The Witcher 4 using NVIDIA’s RTX Mega Geometry to path trace forests for the first time.
Now, NVIDIA has released the full video replay of the GDC 2026 session ‘The Future of Path Tracing | Best Practices, Optimizations & Future Standards‘, which includes lots of interesting details on that The Witcher 4/RTX Mega Geometry demo.
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Martin Stich, Senior Director of Engineering at NVIDIA, introduced the company’s latest work based on Mega Geometry: a level-of-detail system for foliage. He notes that no new APIs or hardware are required, since it is built on the existing Mega Geometry APIs.
The demo scene, which includes tree assets provided by CD Projekt RED (presumably used in the development of The Witcher 4), features 60 million plants of 200 different species and around 1 million trees. It takes place on a 5×5 km terrain, entirely held in memory with no streaming, as evidenced by the lack of any pop-in or other typical LOD issues.
Larger trees have up to and over 10 million polygons each, and everything in the demo is modeled as actual geometry, meaning no alpha maps or cards, down to individual pine needles. Martin’s favorite stat from this demo, though, is that if you flattened the entire scene into a triangle list at full LOD, you would get over 5 trillion triangles. Of course, The Witcher 4’s RTX Mega Geometry foliage demo features fully dynamic path-traced lighting with pixel-perfect shadows, and everything can be uniquely animated.
Each tree’s high polygon count is achieved through the instancing of small sub-objects called “twigs”, the same approach used by Epic’s Unreal Engine for Nanite foliage (introduced with UE 5.7). A typical large tree has a dozen or so individual twig pieces, and each twig is instanced hundreds to a few thousand times across the tree. For animation, each twig/mesh is attached rigidly to a skeleton’s bones rather than being vertex-skinned. Martin notes that vertex skinning could be used for extreme close-ups, but it was not deemed necessary given how small the individual twig objects are.
To avoid blowing up the memory budget, NVIDIA engineers have developed a multi-stage LOD system that progressively merges sub-meshes into fewer instances as distance increases, until at the furthest LOD each tree is a single instance. The animation skeleton is simplified in parallel to keep motion consistent across LOD levels. This, in turn, introduced another potential issue: the merged meshes are now unique combinations that can’t share data, which would blow out memory again.
To solve this, NVIDIA turned to Opacity Micro-Maps (OMMs), originally introduced with the Ada Lovelace architecture (GeForce RTX 40 Series). LODs are generated offline by rasterizing each mesh’s geometry into a set of automatically positioned OMM triangles. Ultimately, Stich clarified that the goal of this LOD system is not to reduce geometric complexity, as the geometry itself stays essentially the same across LODs. The goal is purely to reduce instance count.
Last but certainly not least, Stich revealed a performance breakdown for The Witcher 4’s RTX Mega Geometry foliage demo. What was showcased at GDC 2026 ran at around 80 frames per second at 4K (upscaled from 1440P to 4K with DLSS Quality) on a GeForce RTX 5090, or at 58 frames per second at 1440p (again, upscaled from 960P to 1440P with DLSS Quality) on a GeForce RTX 4070. As you’d expect, most of the frame budget goes to path tracing. In this case, a simple two-bounce path tracer was used. DLSS takes up another chunk between upscaling and denoising with Ray Reconstruction.
Of course, these are work-in-progress figures from a demo of an in-development technology. That said, given that the assets were indeed taken from The Witcher 4 and that the technology itself is confirmed to be featured in the final game, it does give us a hint at the kind of performance needed to run it.
The highly anticipated open world action roleplaying game is expected to launch at some point in 2027. That was also the original estimate for NVIDIA’s GeForce RTX 6000 Series, but a recent report by The Information suggested that memory shortages might delay it into 2028. As such, we may be forced to play The Witcher 4 with existing graphics cards.
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