NVIDIA has released version 1.9.0 of RTX Path Tracing (RTXPT), its open-source reference path tracer on GitHub, claiming roughly 20% better performance than the previous 1.8.1 release, with comparable or better image quality. RTXPT is a code sample for developers, meant as a starting point for building a path tracer or as a reference for NVIDIA's other ray tracing SDKs. Several changes add up to that uplift. The path tracer can now optionally trace only three quarters, half, or a quarter of the pixels each frame, and the built-in performance presets use this by default, along with lower bounce limits in the faster modes.
On DirectX 12, async compute lets the previous frame's DLSS Ray Reconstruction and post-processing overlap with the next frame's path tracing, and TLAS instance generation has moved to the GPU. Lighting got some attention too. NEE-AT light sampling now handles up to 2 million lights, up from 512K, and the SHaRC radiance cache is on by default in real-time mode, apparently feeding more indirect lighting into DLSS Ray Reconstruction at about the same cost. Version 1.9 also adds Windows on ARM64 support. The release notes don't say why, though it's probably no coincidence, given NVIDIA's own Arm-based RTX Spark chip for Windows PCs.