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DirectX Raytracing Update: 90% Less VRAM & Big FPS Boost

Microsoft's Agility SDK 1.722 preview redesigns DXR with Clustered Geometry and PTLAS, slashing ray tracing BVH memory by up to 90% across modern RTX and Radeon GPUs.

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DirectX Raytracing Update: 90% Less VRAM & Big FPS Boost
News / Pixlboard JournalImage / Pixlboard

Microsoft's major DirectX Raytracing (DXR) update cuts VRAM overhead by up to 90% and accelerates BVH builds. We explain Clustered Geometry, PTLAS, and gaming impact.

Clustered Geometry, Partitioned TLAS, and GPU-driven builds — why Microsoft's DXR overhaul matters for PC gamers

Direct Answer: Microsoft's DirectX 12 Agility SDK 1.722 Preview delivers the most significant architectural overhaul to DirectX Raytracing (DXR) since 2018. By introducing Clustered Geometry, Partitioned Top-Level Acceleration Structures (PTLAS), and GPU-Driven Acceleration Structure Builds, the update slashes ray-tracing BVH memory footprints by up to 90% (reducing test scene VRAM allocations from ~7.5 GiB down to 774 MiB) and cuts hierarchy build times from 788 ms to 3.1 ms. Crucially, this requires no new silicon and functions on all existing DirectX 12 Ultimate hardware from NVIDIA, AMD, and Intel.

The Ray Tracing Memory Bottleneck Explained

While hardware ray tracing delivers breathtaking global illumination, reflections, and path-traced shadows, it has historically placed a crushing tax on PC video memory and CPU dispatch threads:

  1. Bounding Volume Hierarchy (BVH) Bloat: For a GPU to trace light rays against millions of game triangles, it must organize them into hierarchical bounding boxes (Bottom-Level Acceleration Structures, or BLAS, and Top-Level Acceleration Structures, or TLAS). In sprawling open-world titles like *Cyberpunk 2077* or *Alan Wake 2*, simply storing these acceleration structures can consume 3 GB to 8 GB of VRAM.
  2. Dynamic Geometry Rebuild Stalls: When characters animate, foliage sways, or destructible environments shatter, the CPU and GPU must continuously recalculate and rebuild bounding boxes from scratch. This causes frame pacing micro-stutters and 1% low frame-rate drops.
  3. The VRAM Allocation Crisis: Combined with 4K textures and high-resolution framebuffers, heavy ray tracing frequently pushes 8 GB and 12 GB GPUs into system memory paging, causing catastrophic framerate collapses.

The Three Architectural Pillars of the DXR Overhaul

Microsoft's Agility SDK 1.722 preview addresses these core limitations through three interconnected rendering innovations:

Architectural FeatureTraditional DXR 1.1 ImplementationNew Agility SDK 1.722 DXR ArchitectureReal-World Benefit
Geometry HandlingMonolithic BLAS built over entire meshesClustered Geometry (subdivided into clusters of ≤256 triangles)Eliminates duplicate geometry allocations; reuses clusters
Scene HierarchyFull TLAS rebuild on every dynamic scene changePartitioned TLAS (PTLAS)Only updates modified scene partitions, skipping static zones
Hierarchy ConstructionCPU-driven command recording & dispatchGPU-Driven AS BuildsDirect GPU execution bypassing CPU thread bottlenecks
VRAM Footprint7.3 GiB - 7.5 GiB (heavy test workload)~774 MiB (identical scene workload)~90% VRAM reduction in acceleration structures
Build Time788 ms3.11 ms99.6% reduction in build latency
Custom liquid-cooled gaming PC with illuminated cooling loop and high-performance components
High-end custom liquid-cooled gaming PC rig featuring dual loop cooling, illuminated reservoir, and performance graphics hardware. Photo by Dave Monk / Wikimedia Commons, licensed under CC BY-SA 2.0.

Deep Dive: How Clustered Geometry & PTLAS Function

1. Clustered Geometry

Similar to how modern geometric virtualization engines (like Unreal Engine 5's Nanite) break meshes into micro-clusters, DXR Clustered Geometry breaks 3D assets down into small, uniform clusters of up to 256 vertices and triangles. When an animated character moves or streams across the camera frustum, only the transformed clusters require acceleration updates rather than recalculating the entire mesh skeleton.

2. Partitioned Top-Level Acceleration Structures (PTLAS)

In an expansive game environment, 90% of the world geometry (terrain, buildings, static props) remains completely unchanged between frames. Previously, updating a few moving vehicles or active combatants forced the engine to re-evaluate the full world TLAS. PTLAS isolates dynamic regions into independent partitions, leaving static bounding hierarchies untouched and slashing compute overhead.

3. Zero New Hardware Required

Unlike proprietary hardware generations that require buying a new graphics card, this DXR overhaul is an API-level architectural improvement. Any GPU supporting DirectX 12 Ultimate—including NVIDIA GeForce RTX 30, 40, and 50 series, AMD Radeon RX 7000 and 9000 series, and Intel Arc graphics—will benefit once game developers integrate the Agility SDK and GPU manufacturers deploy compliant WHQL preview drivers.

Why This Matters During the 2026 Hardware Crunch

With DRAM and GDDR7 memory prices inflated due to enterprise AI demand, gamers cannot simply brute-force VRAM limitations by overspending on flagship GPUs. Architectural efficiency improvements in DirectX 12 provide significant relief:

  • Revitalizes 12 GB and 16 GB GPUs: Graphics cards like the Gigabyte RTX 5060 Ti Eagle OC ICE 16GB gain immense longevity. Slashing ray tracing structure memory by hundreds of megabytes leaves abundant VRAM headroom for high-resolution 1440p textures and AI frame generation buffers.
  • Flattens Frame-Time Spikes: Shifting BVH generation entirely to the GPU eliminates sudden CPU dispatch hiccups during intense combat or scene transitions, delivering rock-solid frame pacing.

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Photo credits & courtesy: Header photograph of high-performance triple-fan GeForce RTX graphics card with reinforced shroud by PantheraLeo1359531 / Wikimedia Commons, licensed under CC BY 4.0. Inline studio photograph of custom liquid-cooled gaming PC rig by Dave Monk / Wikimedia Commons, licensed under CC BY-SA 2.0.

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