Rendering 2024 - Symposium Track

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https://diglib.eg.org/handle/10.2312/3607012

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Browsing Rendering 2024 - Symposium Track by Subject "> Ray tracing"

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    Computing Manifold Next-Event Estimation without Derivatives using the Nelder-Mead Method
    (The Eurographics Association, 2024) Granizo-Hidalgo, Ana; Holzschuch, Nicolas; Haines, Eric; Garces, Elena
    Specular surfaces, by focusing the light that is being reflected or refracted, cause bright spots in the scene, called caustics. These caustics are challenging to compute for global illumination algorithms. Manifold-based methods (Manifold Exploration, Manifold Next-Event Estimation, Specular Next Event Estimation) compute these caustics as the zeros of an objective function, using the Newton-Raphson method. They are efficient, but require computing the derivatives of the objective function, which in turn requires local surface derivatives around the reflection point, which can be challenging to implement. In this paper, we leverage the Nelder-Mead method to compute caustics using Manifold Next-Event Estimation without having to compute local derivatives. Our method only requires local evaluations of the objective function, making it an easy addition to any path-tracing algorithm.
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    Path Sampling Methods for Differentiable Rendering
    (The Eurographics Association, 2024) Su, Tanli; Gkioulekas, Ioannis; Haines, Eric; Garces, Elena
    We introduce a suite of path sampling methods for differentiable rendering of scene parameters that do not induce visibility-driven discontinuities, such as BRDF parameters. We begin by deriving a path integral formulation for differentiable rendering of such parameters, which we then use to derive methods that importance sample paths according to this formulation. Our methods are analogous to path tracing and path tracing with next event estimation for primal rendering, have linear complexity, and can be implemented efficiently using path replay backpropagation. Our methods readily benefit from differential BRDF sampling routines, and can be further enhanced using multiple importance sampling and a loss-aware pixel-space adaptive sampling procedure tailored to our path integral formulation. We show experimentally that our methods reduce variance in rendered gradients by potentially orders of magnitude, and thus help accelerate inverse rendering optimization of BRDF parameters.
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    Ray Traced Stochastic Depth Map for Ambient Occlusion
    (The Eurographics Association, 2024) Brüll, Felix; Kern, René; Grosch, Thorsten; Haines, Eric; Garces, Elena
    Screen-space ambient occlusion is a popular technique for approximating global illumination in real-time rendering. However, it suffers from artifacts due to the lack of information from the depth buffer. A stochastic depth map [VSE21] can be used to retrieve most of the missing information, but it is not suitable for real-time rendering in large scenes. In this paper, we propose a new stochastic depth map acquisition method powered by hardware ray tracing, which shows better performance characteristics than the previous method. We present further improvements that increase the quality and performance of the stochastic depth map generation. Furthermore, the results are almost indistinguishable from a ground truth solution with all depth samples.
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    Real-Time Pixel-Perfect Hard Shadows with Leak Tracing
    (The Eurographics Association, 2024) Kern, René; Brüll, Felix; Grosch, Thorsten; Haines, Eric; Garces, Elena
    Accurate shadows greatly enhance the realism of a rendered image. Shadow mapping is the preferred solution for shadows in real-time applications. However, shadow maps suffer from discretization errors and self-shadowing artifacts, that need custom parameter tuning per scene. Filterable shadow maps such as variance or moment shadow maps solve both issues but introduce light leaking. With the advent of hardware ray tracing, it becomes more realistic to use shadow rays instead of a shadow map. However, distributing a shadow ray is often more expensive than evaluating a shadow map, especially if the ray hits alphatested geometry. We introduce leak tracing, where we use filterable shadow maps techniques on top of default shadow maps and eliminate the light leaks and aliased shadow edges with selective ray tracing. Our algorithm does not need any scene-dependent parameters. We achieve an average speedup ranging from 1.19 to 1.79, with a top speedup of 4.17, depending on the scene and eliminate major performance drops caused by alpha-tested geometry during ray tracing. Our solution is temporally stable and reaches similar quality as pure ray tracing.
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    Robust Cone Step Mapping
    (The Eurographics Association, 2024) Bán, Róbert; Valasek, Gábor; Bálint, Csaba; Vad, Viktor A.; Haines, Eric; Garces, Elena
    Per-pixel displacement mapping provides an alternative to high-fidelity geometry and flat textured faces with in-between performance costs. Although cone maps are known to facilitate efficient and robust rendering of height fields, we show that these cannot guarantee robustness under bilinear interpolation, and we propose corrections to this issue. First, we define an artifactfree minimum step size for the cone map tracing algorithm while remaining comparable in performance to that of Dummer. Second, we modify the cone map generation procedure so that at bilinearly interpolated values the unbounding cones remain disjoint from the heightmap, thereby preventing another source of rendering artifacts. Third, we introduce an exact method to generate relaxed cones such that any ray within intersects the heightmap at most once, in contrast to the original algorithm that is both computationally more expensive and generates incorrect relaxed cones. Finally, we demonstrate the applicability of these algorithm improvements with visual and performance comparisons in our C++ and HLSL implementation.