Integrating Meshlets into Real-Time Hardware-Accelerated Ray Tracing Pipelines using DirectX 12

Sammanfattning

Background. Real-time rendering applications continue to increase in geometric complexity. Meshlets have emerged as an efficient geometry representation for rasterisation through the mesh shader pipeline. However, modern hardware-accelerated ray-tracing pipelines rely on traditional meshes, creating an incompatibility that requires multiple model geometries to be stored and uploaded to the GPU, increasing memory usage. Objectives. This thesis investigates whether meshlets can serve as a unified geometry representation for both rasterisation and ray tracing in a real-time rendering application using DirectX 12. The study is a proof of concept that evaluates the feasibility, limitations, visual correctness, GPU memory usage, and frame-time performance of the meshlet-based ray-tracing approach. Methods. A real-time rendering application was implemented that supports both mesh-based and meshlet-based geometry for rasterisation and ray tracing. Meshlets were represented as procedural primitives in the DirectX Ray Tracing using meshlet-level axis-aligned bounding boxes. The implementation was evaluated on two different GPU platforms, and multiple meshlet configurations were tested by varying the maximum number of triangles per meshlet to analyse their impact on visual output, GPU memory usage, and frame-time performance. Results. The meshlet-based ray tracer produced output that closely matched the mesh-based reference, with only negligible pixel-level differences. GPU memory usage was significantly reduced for the meshlet-based ray-tracing pipeline, approximately 60% lower VRAM consumption than the mesh-based approach. However, the meshlet-based ray tracer exhibited substantially higher frame times than the mesh-based ray tracer, with a worst-case of approximately 29 times slower. This indicates a significant frame time penalty under the evaluated conditions. Conclusions. The results demonstrate that meshlets can be integrated into hardware-accelerated ray tracing pipelines using existing DirectX Ray tracing functionality while preserving visual correctness and substantially reducing the memory usage. However, the increased computational cost of resolving triangle intersections within meshlets leads to significantly worse rendering performance than that of the traditional mesh-based ray tracer. These findings suggest that meshlet-based ray tracing is feasible for providing visually correct output and as a memory-efficient geometry representation, but requires optimisation or hardware support to improve rendering performance.