Rafael Padilla

Rafael Padilla, Kyle Webster, Austin Kim

Over the last decade, advances in GPU hardware have been driven in large part by the demands of real-time graphics, culminating in dedicated hardware ray tracing cores (RT cores). These units accelerate ray scene intersection queries directly in hardware, making physically based ray tracing algorithms increasingly practical for interactive applications. This paper compares and analyzes the performance of two ray-based rendering algorithms: forward path tracing (PT) and wavefront path tracing (WPT). GPU-based PT computes the color of each pixel by having each thread trace a single path to completion, naturally leading to a megakernel approach - while WPT maintains state buffers between specialized kernel invocations to trace path stages simultaneously. We find that WPT affords a ~16% speedup over PT in our implementation. By analyzing traces from NVIDIA Nsight Graphics, we attributed this speedup to WPT's improved cache locality compared to PT. We also find that our implementation does not achieve maximum GPU throughput across any of its units, suggesting that communication and memory latency, as well as synchronization, are the limiting factors. Finally, we address potential algorithmic improvements and future work for real-time path tracing implementation for practical applications.

Rafael Padilla, Andrew Tate, Dhruv Ram et al.

Hierarchical Progressive Rendering (HiPR) is a dynamic render-scheduling algorithm that makes interactive path tracing finally feel real-time. While most renderers recompute the entire frame after any change to the scene, our method updates some of the pixels based on a priority order while keeping the others unchanged. Rather than relying on error-driven or temporal reuse heuristics, it amortizes rendering costs by organizing pixels into a hierarchy of light-path dependencies from changed elements outward, prioritizing by perceptual impact and delivering instant visual feedback, while eventually converging to an unbiased result.