High-Performance Graphics 2023 - Symposium Papers

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    Clouds in the Cloud: Efficient Cloud-Based Rendering of Real-Time Volumetric Clouds
    (The Eurographics Association, 2023) Weinrauch, Alexander; Lorbek, Stephan; Tatzgern, Wolfgang; Stadlbauer, Pascal; Steinberger, Markus; Bikker, Jacco; Gribble, Christiaan
    Volumetric clouds play a crucial role in creating realistic, dynamic, and immersive virtual outdoor environments. However, rendering volumetric clouds in real-time presents a significant computational challenge on end-user devices. In this paper, we investigate the viability of moving computations to remote servers in the cloud and sharing them among many viewers in the same virtual world, without compromising the perceived quality of the final renderings. We propose an efficient rendering method for volumetric clouds and cloud shadows utilizing caches placed in the cloud layers and directly on the surface of objects. Volumetric cloud properties, like density and lightning, are cached on spheres positioned to represent cloud layers at varying heights. Volumetric cloud shadows are cached directly on the surfaces of receiving objects. This allows efficient rendering in scenarios where multiple viewers observe the same cloud formations by sharing redundant calculations and storing them over multiple frames. Due to the placement and structure of our caches, viewers on the ground still perceive plausible parallax under movement on the ground. In a user study, we found that viewers hardly perceive quality reductions even when computations are shared for viewers that are hundreds of meters apart. Due to the smoothness of the appearance of clouds, caching structures can use significantly reduced resolution and as such allow for efficient rendering even in single-viewer scenarios. Our quantitative experiments demonstrate computational cost savings proportional to the number of viewers placed in the scene when relying on our caches compared to traditional rendering.
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    Compressed Opacity Maps for Ray Tracing
    (The Eurographics Association, 2023) Fenney, Simon; Ozkan, Alper; Bikker, Jacco; Gribble, Christiaan
    Recently, schemes have been proposed for accelerating 'alpha-tested' triangles in ray-tracing through the use of precomputed, three-level Opacity Masks/Maps that can significantly reduce the need for expensive of 'Any-Hit shader' invocations. We propose and compare two related schemes, VQ2 and VQ4, of compressing such maps that provide both random access and low-cost decompression. Each compressed opacity map, however, relates to a pair of adjacent triangles, taking advantage of correlation across the shared edge and matching likely underlying hardware primitive models.
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    Efficient Rendering of Participating Media for Multiple Viewpoints
    (The Eurographics Association, 2023) Stojanovic, Robert; Weinrauch, Alexander; Tatzgern, Wolfgang; Kurz, Andreas; Steinberger, Markus; Bikker, Jacco; Gribble, Christiaan
    Achieving realism in modern games requires the integration of participating media effects, such as fog, dust, and smoke. However, due to the complex nature of scattering and partial occlusions within these media, real-time rendering of high-quality participating media remains a computational challenge. To address this challenge, traditional approaches of real-time participating media rendering involve storing temporary results in a view-aligned grid before ray marching through these cached values. In this paper, we investigate alternative hybrid worldand view-aligned caching methods that allow for the sharing of intermediate computations across cameras in a scene. This approach is particularly relevant for multi-camera setups, such as stereo rendering for VR and AR, local split-screen games, or cloud-based rendering for game streaming, where a large number of players may be in the same location. Our approach relies on a view-aligned grid for near-field computations, which enables us to capture high-frequency shadows in front of a viewer. Additionally, we use a world-space caching structure to selectively activate distant computations based on each viewer's visibility, allowing for the sharing of computations and maintaining high visual quality. The results of our evaluation demonstrate computational savings of up to 50% or more, without compromising visual quality.
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    High-Performance Graphics 2023 Symposium Track: Frontmatter
    (The Eurographics Association, 2023) Bikker, Jacco; Gribble, Christiaan; Bikker, Jacco; Gribble, Christiaan
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    Massively Parallel Adaptive Collapsing of Edges for Unstructured Tetrahedral Meshes
    (The Eurographics Association, 2023) Ströter, Daniel; Stork, André; Fellner, Dieter W.; Bikker, Jacco; Gribble, Christiaan
    Many tasks in computer graphics and engineering involve unstructured tetrahedral meshes. Numerical methods such as the finite element method (FEM) oftentimes use tetrahedral meshes to compute a solution for complex problems such as physicallybased simulation or shape deformation. As each tetrahedron costs computationally, coarsening tetrahedral meshes typically reduces the overhead of numerical methods, which is attractive for interactive applications. In order to enable reduction of the tetrahedron count, we present a quick adaptive coarsening method for unstructured tetrahedral meshes. Our method collapses edges using the massively parallel processing power of present day graphics processing units (GPU)s to achieve run times of up to one order of magnitude faster than sequential collapsing. For efficient exploitation of parallel processing power, we contribute a quick method for finding a compact set of conflict-free sub-meshes, which results in up to 59% fewer parallel collapsing iterations compared to the state of the art massively parallel conflict detection.
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    Minimal Convolutional Neural Networks for Temporal Anti Aliasing
    (The Eurographics Association, 2023) Herveau, Killian; Piochowiak, Max; Dachsbacher, Carsten; Bikker, Jacco; Gribble, Christiaan
    Existing deep learning methods for performing temporal anti aliasing (TAA) in rendering are either closed source or rely on upsampling networks with a large operation count which are expensive to evaluate. We propose a simple deep learning architecture for TAA combining only a few common primitives, easy to assemble and to change for application needs. We use a fully-convolutional neural network architecture with recurrent temporal feedback, motion vectors and depth values as input and show that a simple network can produce satisfactory results. Our architecture template, for which we provide code, introduces a method that adapts to different temporal subpixel offsets for accumulation without increasing the operation count. To this end, convolutional layers cycle through a set of different weights per temporal subpixel offset while their operations remain fixed. We analyze the effect of this method on image quality and present different tradeoffs for adapting the architecture. We show that our simple network performs remarkably better than variance clipping TAA, eliminating both flickering and ghosting without performing upsampling.
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    Neural Intersection Function
    (The Eurographics Association, 2023) Fujieda, Shin; Kao, Chih Chen; Harada, Takahiro; Bikker, Jacco; Gribble, Christiaan
    The ray casting operation in the Monte Carlo ray tracing algorithm usually adopts a bounding volume hierarchy (BVH) to accelerate the process of finding intersections to evaluate visibility. However, its characteristics are irregular, with divergence in memory access and branch execution, so it cannot achieve maximum efficiency on GPUs. This paper proposes a novel Neural Intersection Function based on a multilayer perceptron whose core operation contains only dense matrix multiplication with predictable memory access. Our method is the first solution integrating the neural network-based approach and BVH-based ray tracing pipeline into one unified rendering framework. We can evaluate the visibility and occlusion of secondary rays without traversing the most irregular and time-consuming part of the BVH and thus accelerate ray casting. The experiments show the proposed method can reduce the secondary ray casting time for direct illumination by up to 35% compared to a BVH-based implementation and still preserve the image quality.
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    PSAO: Point-Based Split Rendering for Ambient Occlusion
    (The Eurographics Association, 2023) Neff, Thomas; Budge, Brian; Dong, Zhao; Schmalstieg, Dieter; Steinberger, Markus; Bikker, Jacco; Gribble, Christiaan
    Recent advances in graphics hardware have enabled ray tracing to produce high-quality ambient occlusion (AO) in real-time, which is not plagued by the artifacts typically found in real-time screen-space approaches. However, the high computational cost of ray tracing remains a significant hurdle for low-power devices like standalone VR headsets or smartphones. To address this challenge, inspired by point-based global illumination and texture-space split rendering, we propose point-based split ambient occlusion (PSAO), a novel split-rendering system that streams points sparsely from server to client. PSAO first evenly distributes points across the scene, and then subsequently only transmits points that changed more than a given threshold, using an efficient hash grid to blend neighboring points for the final compositing pass on the client. PSAO outperforms recent texture-space shading approaches in terms of quality and required network bit rate, while demonstrating performance similar to commonly used lower-quality screen-space approaches. Our point-based split rendering representation lends itself to highly compressible signals such as AO and is scalable towards quality or bandwidth requirements by adjusting the number of points in the scene.
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    Spherical Parametric Measurement for Continuous and Balanced Mesh Segmentation
    (The Eurographics Association, 2023) Zhang, Huadong; Cao, Lizhou; Peng, Chao; Bikker, Jacco; Gribble, Christiaan
    Mesh segmentation is an important process for building the discrete mesh structure used on the GPU to accelerate geometry processing applications. In this paper, we introduce a novel mesh segmentation method that creates balanced sub-meshes for high-performance geometry processing. The method ensures topological continuity within sub-meshes (segments) and evenly distributes the number of triangles across all sub-meshes. A new cohesion algorithm computes the chord distances between triangles in the spherical domain and re-groups the triangles into the sub-meshes based on a distance-based measurement condition. A new refinement algorithm between the neighboring sub-meshes is conducted to resolve the non-manifold issue and improve the boundary smoothness. Both algorithms are executed in a parallel fashion. In advancing the state-of-the-art, our approach achieves exactly balanced triangle counts and mitigates the non-manifold issue significantly. The algorithms require the input meshes to have a closed-manifold genus of zero, which is a constraint that is commonly associated with the concept of sphere-based parameterization. We evaluated the effectiveness of our approach in supporting two geometry processing applications. The results show that the performance is enhanced by leveraging the structure of the balanced sub-meshes from our approach.
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    Surface Light Cones: Sharing Direct Illumination for Efficient Multi-viewer Rendering
    (The Eurographics Association, 2023) Stadlbauer, Pascal; Weinrauch, Alexander; Tatzgern, Wolfgang; Steinberger, Markus; Bikker, Jacco; Gribble, Christiaan
    Even though stochastic methods and hardware supported ray tracing are increasingly used for computing direct illumination, the efficient real-time rendering of dynamic area light sources still forms a challenge. In this paper, we propose a method for representing and caching direct illumination information using a compact multi-cone representation that is stored on the surface of objects. While shading due to direct illumination is typically heavily view-dependent, the incoming radiance for surface points is view-independent. Relying on cones, to represent the projection of the dominant visible light sources, allows to reuse the incoming radiance information across frames and even among multiple cameras or viewers within the same scene. Progressively refining and updating the cone structures not only allows to adapt to dynamic scenes, but also leads to reduced noise levels in the output images compared to sampling based methods. Relying on surface light cones allows to render single viewer setups 2-3x faster than random sampling, and 1.5-2x faster than reservoir-based sampling with the same quality. The main selling point for surface light cones is multi-camera rendering, For stereo rendering, our approach essentially halves the time required for determining direct light visibility. For rendering in the cloud, where multiple viewers are positioned close to another, such as in virtual meetings, gathering locations in games, or online events such as virtual concerts, our approach can reduce overall rendering times by a factor of 20x for as few as 16 viewers in a scene compared to traditional light sampling. Finally, under heavily constraint ray budgets where noise levels typically overshadow bias, surface light cones can dramatically reduce noise.
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    Voxel-based Representations for Improved Filtered Appearance
    (The Eurographics Association, 2023) Brito, Caio José Dos Santos; Poulin, Pierre; Teichrieb, Veronica; Bikker, Jacco; Gribble, Christiaan
    Volumetric representations allow filtering of mesh-based complex 3D scenes to control both the efficiency and quality of rendering. Unfortunately, directional variations in the visual appearance of a volume still hinder its adoption by the real-time rendering community. To alleviate this problem, we propose two simple structures: (1) a virtual mesh to encode the directional distribution of colors and normals, and (2) a low-resolution subgrid of opacities to encode directional visibility. We precompute these structures from a mesh-based scene into a regular voxelization. During display, we use simple rendering methods on the two structures to compute the image contribution of the appearance of a visible voxel, optimizing for efficiency and/or quality. The improved visual results compared to previous work are a step forward to the integration of volumetric representations in real-time rendering.