High-Performance Graphics 2019 - Short Papers

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Dynamic Many-Light Sampling for Real-Time Ray Tracing
(The Eurographics Association, 2019) Moreau, Pierre; Pharr, Matt; Clarberg, Petrik; Steinberger, Markus and Foley, Tim
Monte Carlo ray tracing offers the capability of rendering scenes with large numbers of area light sources-lights can be sampled stochastically and shadowing can be accounted for by tracing rays, rather than using shadow maps or other rasterizationbased techniques that do not scale to many lights or work well with area lights. Current GPUs only afford the capability of tracing a few rays per pixel at real-time frame rates, making it necessary to focus sampling on important light sources. While state-of-the-art algorithms for offline rendering build hierarchical data structures over the light sources that enable sampling them according to their importance, they lack efficient support for dynamic scenes. We present a new algorithm for maintaining hierarchical light sampling data structures targeting real-time rendering. Our approach is based on a two-level BVH hierarchy that reduces the cost of partial hierarchy updates. Performance is further improved by updating lower-level BVHs via refitting, maintaining their original topology. We show that this approach can give error within 6% of recreating the entire hierarchy from scratch at each frame, while being two orders of magnitude faster, requiring less than 1 ms per frame for hierarchy updates for a scene with thousands of moving light sources on a modern GPU. Further, we show that with spatiotemporal filtering, our approach allows complex scenes with thousands of lights to be rendered with ray-traced shadows in 16.1 ms per frame.
High-Performance Graphics 2019 – Short Papers: Frontmatter
(Eurographics Association, 2019) Steinberger, Markus; Foley, Tim; Steinberger, Markus and Foley, Tim
Mach-RT: A Many Chip Architecture for Ray Tracing
(The Eurographics Association, 2019) Vasiou, Elena; Shkurko, Konstantin; Brunvand, Erik; Yuksel, Cem; Steinberger, Markus and Foley, Tim
We propose an unconventional solution to high-performance ray tracing that combines a ray ordering scheme that minimizes access to the scene data with a large on-chip buffer acting as near-compute storage that is spread over multiple chips. We demonstrate the effectiveness of our approach by introducing Mach-RT (Many chip - Ray Tracing), a new hardware architecture for accelerating ray tracing. Extending the concept of dual streaming, we optimize the main memory accesses to a level that allows the same memory system to service multiple processor chips at the same time. While a multiple chip solution might seem to imply increased energy consumption as well, because of the reduced memory traffic we are able to demonstrate, performance increases while maintaining reasonable energy usage compared to academic and commercial architectures.
Patch Textures: Hardware Implementation of Mesh Colors
(The Eurographics Association, 2019) Mallett, Ian; Seiler, Larry; Yuksel, Cem; Steinberger, Markus and Foley, Tim
Mesh colors provide an effective alternative to standard texture mapping. They significantly simplify the asset production pipeline by removing the need for defining a mapping and eliminate rendering artifacts due to seams. This paper addresses the problem that using mesh colors for real-time rendering has not been practical, due to the absence of hardware support. We show that it is possible to provide full hardware texture filtering support for mesh colors with minimal changes to existing GPUs by introducing a hardware-friendly representation for mesh colors that we call patch textures. We discuss the hardware modifications needed for storing and filtering patch textures.
A Practical and Efficient Approach for Correct Z-Pass Stencil Shadow Volumes
(The Eurographics Association, 2019) Usta, Baran; Scandolo, Leonardo; Billeter, Markus; Marroquim, Ricardo; Eisemann, Elmar; Steinberger, Markus and Foley, Tim
Shadow volumes are a popular technique to compute pixel-accurate hard shadows in 3D scenes. Many variants exist that trade off accuracy and efficiency. In this work, we present an artifact-free, efficient, and easy-to-implement stencil shadow volume method. We compare our method to established stencil shadow volume techniques and show that it outperforms the alternatives.
Real-Time Ray Tracing on Head-Mounted-Displays for Advanced Visualization of Sheet Metal Stamping Defects
(The Eurographics Association, 2019) Dietrich, Andreas; Wurster, Jan; Kam, Eric; Gierlinger, Thomas; Steinberger, Markus and Foley, Tim
Although interactive ray tracing has been around since the late 1990s, real-time frame rates had so far only been feasible for low and mid-size screen resolutions. Recent developments in GPU hardware, that specifically accelerate ray tracing, make it possible for the first time to target head-mounted displays (HMDs), which require constant high frame rates as well as high resolution images for each eye. This allows for utilizing ray tracing algorithms in novel virtual reality scenarios, which are impractical to do with rasterization. In this short paper we present our experiences of applying real-time ray tracing to the problem of detecting cosmetic defects in sheet metal stamping simulations by creating a virtual light cage.
RTX Beyond Ray Tracing: Exploring the Use of Hardware Ray Tracing Cores for Tet-Mesh Point Location
(The Eurographics Association, 2019) Wald, Ingo; Usher, Will; Morrical, Nathan; Lediaev, Laura; Pascucci, Valerio; Steinberger, Markus and Foley, Tim
We explore a first proof-of-concept example of creatively using the Turing generation's hardware ray tracing cores to solve a problem other than classical ray tracing, specifically, point location in unstructured tetrahedral meshes. Starting with a CUDA reference method, we describe and evaluate three different approaches to reformulate this problem in a manner that allows it to be mapped to these new hardware units. Each variant replaces the simpler problem of point queries with the more complex one of ray queries; however, thanks to hardware acceleration, these approaches are actually faster than the reference method.
Stochastic Lightcuts
(The Eurographics Association, 2019) Yuksel, Cem; Steinberger, Markus and Foley, Tim
We introduce stochastic lightcuts by combining the lighting approximation of lightcuts with stochastic sampling for efficiently rendering scenes with a large number of light sources. Our stochastic lightcuts method entirely eliminates the sampling correlation of lightcuts and replaces it with noise. To minimize this noise, we present a robust hierarchical sampling strategy, combining the benefits of importance sampling, adaptive sampling, and stratified sampling. Our approach also provides temporally stable results and lifts any restrictions on the light types that can be approximated with lightcuts. We present examples of using stochastic lightcuts with path tracing as well as indirect illumination with virtual lights, achieving more than an order of magnitude faster render times than lightcuts by effectively approximating direct illumination using a small number of light samples, in addition to providing temporal stability. Our comparisons to other stochastic sampling techniques demonstrate that we provide superior sampling quality that matches and improves the excellent convergence rates of the lightcuts approach.
Temporally Dense Ray Tracing
(The Eurographics Association, 2019) Andersson, Pontus; Nilsson, Jim; Salvi, Marco; Spjut, Josef; Akenine-Möller, Tomas; Steinberger, Markus and Foley, Tim
We present a technique for real-time ray tracing with the goal of reaching 240 frames per second or more. The core idea is to trade spatial resolution for faster temporal updates in such a way that the display and human visual system aid in integrating high-quality images. We use a combination of frameless and interleaved rendering concepts together with ideas from temporal antialiasing algorithms and novel building blocks-the major one being adaptive selection of pixel orderings within tiles, which reduces spatiotemporal aliasing significantly. The image quality is verified with a user study. Our work can be used for esports or any kind of rendering where higher frame rates are needed.
Wide BVH Traversal with a Short Stack
(The Eurographics Association, 2019) Vaidyanathan, Karthik; Woop, Sven; Benthin, Carsten; Steinberger, Markus and Foley, Tim
Compressed wide bounding volume hierarchies can significantly improve the performance of incoherent ray traversal, through a smaller working set of inner nodes and therefore a higher cache hit rate. While inner nodes in the hierarchy can be compressed, the size of the working set for a full traversal stack remains a significant overhead. In this paper we introduce an algorithm for wide bounding volume hierarchy (BVH) traversal that uses a short stack of just a few entries. This stack can be fully stored in scarce on-chip memory, which is especially important for GPUs and dedicated ray tracing hardware implementations. Our approach in particular generalizes the restart trail algorithm for binary BVHs to BVHs of arbitrary widths. Applying our algorithm to wide BVHs, we demonstrate that the number of traversal steps with just five stack entries is close to that of a full traversal stack. We also propose an extension to efficiently cull leaf nodes when a closer intersection has been found, which reduces ray primitive intersections by up to 14%.

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