Browsing by Author "Pharr, Matt"

Now showing 1 - 7 of 7
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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.
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    Fast Procedural Noise By Monte Carlo Sampling
    (The Eurographics Association, 2023) Fajardo, Marcos; Pharr, Matt; Ritschel, Tobias; Weidlich, Andrea
    Procedural noise functions are widely used in computer graphics as a way to add texture detail to surfaces and volumes. Many noise functions are based on weighted sums that can be expressed in terms of random variables, which makes it possible to compute Monte Carlo estimates of their values at lower cost. Such stochastic noise functions fit naturally into many Monte Carlo estimators already used in rendering. Leveraging the dense image-plane sampling in modern path tracing renderers, we show that stochastic evaluation allows the use of procedural noise at a fraction of its full cost with little additional error.
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    Practical Product Sampling by Fitting and Composing Warps
    (The Eurographics Association and John Wiley & Sons Ltd., 2020) Hart, David; Pharr, Matt; Müller, Thomas; Lopes, Ward; McGuire, Morgan; Shirley, Peter; Dachsbacher, Carsten and Pharr, Matt
    We introduce a Monte Carlo importance sampling method for integrands composed of products and show its application to rendering where direct sampling of the product is often difficult. Our method is based on warp functions that operate on the primary samples in [0;1)^n, where each warp approximates sampling a single factor of the product distribution. Our key insight is that individual factors are often well-behaved and inexpensive to fit and sample in primary sample space, which leads to a practical, efficient sampling algorithm. Our sampling approach is unbiased, easy to implement, and compatible with multiple importance sampling. We show the results of applying our warps to projected solid angle sampling of spherical triangles, to sampling bilinear patch light sources, and to sampling glossy BSDFs and area light sources, with efficiency improvements of over 1.6 x on real-world scenes.
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    Rendering 2020 CGF 39-4: Frontmatter
    (The Eurographics Association and John Wiley & Sons Ltd., 2020) Dachsbacher, Carsten; Pharr, Matt; Dachsbacher, Carsten and Pharr, Matt
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    Rendering 2020 DL Track: Frontmatter
    (The Eurographics Association, 2020) Dachsbacher, Carsten; Pharr, Matt; Dachsbacher, Carsten and Pharr, Matt
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    ReSTIR GI: Path Resampling for Real-Time Path Tracing
    (The Eurographics Association and John Wiley & Sons Ltd., 2021) Ouyang, Yaobin; Liu, Shiqiu; Kettunen, Markus; Pharr, Matt; Pantaleoni, Jacopo; Binder, Nikolaus and Ritschel, Tobias
    Even with the advent of hardware-accelerated ray tracing in modern GPUs, only a small number of rays can be traced at each pixel in real-time applications. This presents a significant challenge for path tracing, even when augmented with state-of-the art denoising algorithms. While the recently-developed ReSTIR algorithm [BWP*20] enables high-quality renderings of scenes with millions of light sources using just a few shadow rays at each pixel, there remains a need for effective algorithms to sample indirect illumination. We introduce an effective path sampling algorithm for indirect lighting that is suitable to highly parallel GPU architectures. Building on the screen-space spatio-temporal resampling principles of ReSTIR, our approach resamples multi-bounce indirect lighting paths obtained by path tracing. Doing so allows sharing information about important paths that contribute to lighting both across time and pixels in the image. The resulting algorithm achieves a substantial error reduction compared to path tracing: at a single sample per pixel every frame, our algorithm achieves MSE improvements ranging from 9.3x to 166x in our test scenes. In conjunction with a denoiser, it leads to high-quality path traced global illumination at real-time frame rates on modern GPUs.
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    A Taxonomy of Bidirectional Scattering Distribution Function Lobes for Rendering Engineers
    (The Eurographics Association, 2020) McGuire, Morgan; Dorsey, Julie; Haines, Eric; Hughes, John F.; Marschner, Steve; Pharr, Matt; Shirley, Peter; Klein, Reinhard and Rushmeier, Holly
    We propose a taxonomy and terminology for rendering engineers to use in describing the main categories of mathematical lobes that are combined to implement bidirectional scattering distribution functions (BSDFs). Bringing consistent language to this area will increase clarity in API names, textbooks, and scholarly publications. We developed this taxonomy and terminology for consistency across our own upcoming works. The taxonomy corresponds to the major BSDF implementation branches in a renderer, rather than surface appearance, and is consistent with physical considerations. The terminology aligns as closely as possible with previous work in rendering and adjacent fields, while resolving inconsistencies among them. The taxonomy is not intended for art direction, machine vision research, optics, material/lighting engineering, or other areas where the critical distinctions between materials differ from those needed by a renderer.