Occlusion-Point Reuse for Ray-Traced Ambient Occlusion and Shadow

2026-07-25

AI Summary

Real-time hardware-accelerated ray tracing suffers from high noise and computational cost in ambient occlusion (AO) and soft shadow estimation due to limited samples per pixel. This work proposes an occluder point reuse framework that unifies AO and area-light shadow estimation as integrals over the occluder domain. By reusing ray samples within neighborhoods of first-hit occluder points and combining unbiased and biased estimators through multiple importance sampling, the method achieves efficient sample reuse guided by occluder consistency rather than traditional visibility consistency, better aligning with scene geometry. Experiments demonstrate that, at comparable computational cost, the proposed approach outperforms non-reuse baselines in both AO and soft shadow quality, and further surpasses existing light-sample reuse techniques in shadow fidelity.

Abstract

Ambient occlusion (AO) and soft shadows are critical visibility cues for spatial perception in real-time rendering. Hardware ray tracing provides a direct way to evaluate these effects, enabling ray-traced AO and area-light shadows that avoid many limitations of screen-space AO and shadow mapping. However, real-time budgets allow only a few rays per pixel, leaving raw ray-traced estimates noisy and expensive. We present an occlusion-point reuse framework that reuses traced samples in the domain of first-hit occlusion points instead of directly reusing final shading values or light samples. This provides a ray-reuse formulation for AO, rather than merely filtering or reusing completed AO values. The key idea is to transform AO and area-light shadow estimators into occluder-domain integrals, then combine neighboring occluder samples with a multiple-importance-sampling (MIS) formulation. For both AO and shadows, we derive unbiased estimators that validate convergence to the transformed integrals, as well as biased estimators designed for practical real-time execution. The biased variants assume local first-hit occluder consistency; for shadows, this occluder-based assumption better matches local visibility geometry than the visibility-consistency assumption commonly used when reusing light samples. Experiments show higher AO and shadow quality than non-reuse ray-traced baselines, and better shadow quality than light-sample reuse at comparable cost.

Problem

• ambient occlusion
• soft shadows
• ray tracing
• real-time rendering
• occlusion-point reuse

Innovation

• occlusion-point reuse
• ray tracing
• ambient occlusion
• soft shadows
• multiple importance sampling