AMD showcases new ray-tracing tech that uses 47X less memory with 90X faster performance

AMD has showcased a large-scale terrain demo with around 25,000 independently animated plants and full ray tracing, using a brand-new "tetrahedral cages" method for bounding volume hierarchy (BVH). The result is a smooth 60+ FPS at 1080p running natively on a Radeon RX 9070 XT, and it's an impressive achievement.

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Even though the new "tetrahedral cages" reduce ray-traced triangles from 2.8 billion per frame to around 500 million, the big win is that VRAM drops from 80GB to just 1.7GB. Not only that, but the render time also drops from 300ms down to 3.3ms for all BVH updates per frame. As the name suggests, the tetrahedral cage technique removes the overhead of traditional implementations that must store and update a scene's "geometry state" for every small movement.

Tetrahedral cages store these dense meshes in a deformable cage, allowing BVH structures to remain static and reusable. AMD notes that at runtime, the cage deforms, and rays are compared to a static reference frame before intersecting them with the denser triangles. AMD says this means animation cost scales only with "cage complexity," not the number of triangles inside.

The downside is that you lose animation control over every vertex, which is why it's a technology purpose-built for dense environments like forests and fields of grass and plant life. In these scenarios, an animator is unlikely to animate every blade of grass and instead would use physics-based wind effects or other animations to create a living environment.

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Frequently Asked Questions

Open a question for an answer from TweakTown's coverage of this news, or ask your own below.

Question #1

How do tetrahedral cages work with DXR in AMD's ray-tracing pipeline?

Tetrahedral cages let AMD keep the BVH static and reusable by putting dense meshes inside a deformable cage instead of updating all the geometry state every frame. At runtime, the cage deforms, and rays are compared against that static reference frame before being tested against the denser triangles, so the animation cost scales with cage complexity rather than the number of triangles inside. AMD says this can be combined with Microsoft DirectX Raytracing, but the source does not spell out any deeper DXR pipeline details beyond that compatibility.

Question #2

Why does the tetrahedral cage approach reduce VRAM use so much compared with traditional BVH updates?

It reduces VRAM use because dense meshes are stored inside a deformable tetrahedral cage, so the BVH can stay static and reusable instead of constantly storing and updating geometry state for every small movement. AMD says that shifts the runtime cost to the cage itself, so the memory and animation work scale with cage complexity rather than with the number of triangles inside. That is why the method fits dense scenes like grass and forests so well.

Question #3

Does using tetrahedral cages limit how animators can control individual meshes or vertices?

Yes. The technique means animators lose control over every vertex, because the meshes are stored in a deformable cage instead of being updated as fully editable geometry. It is aimed at dense environments like forests and grass, where full per-vertex animation is not practical.

Question #4

What needs to happen before AMD's tetrahedral cages can be used in actual game engines?

It still needs to move out of the research phase and be adopted by future graphics hardware and game engines. AMD says the technique can already work with Microsoft DirectX Raytracing, so the next step is for it to be integrated into actual game development and shipping hardware.

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Right now, the technology is still in the research phase. Still, we could see it make its way to the current RDNA 4 generation alongside the next generation of graphics hardware, and even consoles like the PlayStation 6, at some point in the near future. AMD confirms that you can combine tetrahedral cages with Microsoft DirectX Raytracing (DXR), so there's a good chance we'll see this in a game at some point, especially with its massive gains to performance and memory optimization.