DirectX Clustered Geometry Preview Could Cut Ray Tracing Memory by up to 90%

Microsoft has published a preview of two new DirectX Raytracing features, Clustered Geometry and Partitioned TLAS. In its own test, the memory used by ray tracing data fell by about 90 percent. The headline number is real, but Microsoft itself says games should not expect that size of gain. Here is what the two sources say, and what it means for a PC gamer.

What changed

Ray tracing needs a map of the scene, which the GPU builds from the models in the game. Microsoft's post says that when a character animates, a tree sways or a model streams in at a new level of detail, the GPU often has to rebuild that object's map from scratch, and that can be very costly. TechSpot adds that this is why many ray-traced games use cheaper, lower-detail copies of the scenery instead of the models you actually see.

Clustered Geometry splits a model into small chunks of triangles that are built once and reused. When an object changes, developers can reassemble existing clusters or rebuild only a few of them. Partitioned TLAS does something similar for the whole scene: it divides the world into regions so that only the parts where something moved are updated each frame. TechSpot says Microsoft describes the pair as the biggest change to DirectX Raytracing since the API arrived in 2018.

The numbers from Microsoft's test

Microsoft ran a demo forest scene from NVIDIA with more than 60 million plants on an AMD Radeon RX 9070. Compared with rebuilding the objects in the usual way:

• Frame rate went from 1.2 fps to 79 fps.
• Time spent building ray tracing data per frame fell from 788 ms to 3.11 ms.
• The memory for all ray tracing structures fell from 7,519 MiB to 774 MiB, which is 89.7 percent less.

Two limits matter. First, the saving applies only to the ray tracing data, not to the total video memory a game uses. Second, Microsoft wrote in capital letters that games should not assume wins of this size, because the scene is a test playground. The post also says clustered builds need much more temporary scratch memory while they work, which developers will have to plan for.

What you need

Nothing new to buy, according to both sources. The post lists support on all NVIDIA RTX GPUs, AMD Radeon RX 9000 series cards, and Intel Arc B-series and recent Core Ultra chips. Support for some older ray tracing GPUs is still undetermined, and Qualcomm Snapdragon X2 drivers are targeted for 2027.

The feature is a preview. It needs a preview version of the Agility SDK and Windows Developer Mode, so it is for developers right now. No game uses it yet through DirectX, and Microsoft gives no date for a final release.

Not a new idea

TechSpot notes that NVIDIA has shipped a similar idea since last year as RTX Mega Geometry, used in Alan Wake 2 and in Gears of War: E-Day. The difference is that this one becomes part of DirectX, so developers get one path that works across vendors. TechSpot also points out that, going by Gears, NVIDIA's version asks for a GeForce card with at least 12 GB of video memory.

What this means for you

Nothing changes in your games today. If this reaches games, the likely benefit is more detailed ray-traced scenes with animated objects, and less pressure on video memory. How much depends on the developer. Our guide to DirectStorage covers another DirectX feature that also needs game support to matter. We will update this article when a game or a final release is announced.