38-Issue 8

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    HMLFC: Hierarchical Motion-Compensated Light Field Compression for Interactive Rendering
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Pratapa, Srihari; Manocha, Dinesh; Steinberger, Markus and Foley, Tim
    We present a new motion-compensated hierarchical compression scheme (HMLFC) for encoding light field images (LFI) that is suitable for interactive rendering. Our method combines two different approaches, motion compensation schemes and hierarchical compression methods, to exploit redundancies in LFI. The motion compensation schemes capture the redundancies in local regions of the LFI efficiently (local coherence) and the hierarchical schemes capture the redundancies present across the entire LFI (global coherence). Our hybrid approach combines the two schemes effectively capturing both local as well as global coherence to improve the overall compression rate. We compute a tree from LFI using a hierarchical scheme and use phase shifted motion compensation techniques at each level of the hierarchy. Our representation provides random access to the pixel values of the light field, which makes it suitable for interactive rendering applications using a small run-time memory footprint. Our approach is GPU friendly and allows parallel decoding of LF pixel values. We highlight the performance on the two-plane parameterized light fields and obtain a compression ratio of 30-800x with a PSNR of 40-45 dB. Overall, we observe a 2-5x improvement in compression rates using HMLFC over prior light field compression schemes that provide random access capability. In practice, our algorithm can render new views of resolution 512x512 on an NVIDIA GTX-980 at around 200 fps.
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    Position-Based Simulation of Elastic Models on the GPU with Energy Aware Gauss-Seidel Algorithm
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Cetinaslan, Ozan; Steinberger, Markus and Foley, Tim
    In this paper, we provide a smooth extension of the energy aware Gauss-Seidel iteration to the Position-Based Dynamics (PBD) method. This extension is inspired by the kinetic and potential energy changes equalization and uses the foundations of the recent extended version of PBD algorithm (XPBD). The proposed method is not meant to conserve the total energy of the system and modifies each position constraint based on the equality of the kinetic and potential energy changes within the Gauss-Seidel process of the XPBD algorithm. Our extension provides an implicit solution for relatively better stiffness during the simulation of elastic objects. We apply our solution directly within each Gauss-Seidel iteration and it is independent of both simulation step-size and integration methods. To demonstrate the benefits of our proposed extension with higher frame rates, we develop an efficient and practical mesh coloring algorithm for the XPBD method which provides parallel processing on a GPU. During the initialization phase, all mesh primitives are grouped according to their connectivity. Afterwards, all these groups are computed simultaneously on a GPU during the simulation phase. We demonstrate the benefits of our method with many spring potential and strain-based continuous material constraints. Our proposed algorithm is easy to implement and seamlessly fits into the existing position-based frameworks.
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    An Analysis of Region Clustered BVH Volume Rendering on GPU
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Ganter, David; Manzke, Michael; Steinberger, Markus and Foley, Tim
    We present a Direct Volume Rendering method that makes use of newly available Nvidia graphics hardware for Bounding Volume Hierarchies. Using BVHs for DVR has been overlooked in recent research due to build times potentially impeding interactive rates. We indicate that this is not necessarily the case, especially when a clustering algorithm is applied before the BVH build to reduce leaf-node complexity. Our results show substantial render time improvements for full-resolution DVR on GPU in comparison to a recent state-of-the-art approach for empty-space-skipping. Furthermore, the use of a BVH for DVR allows seamless integration into popular surface-based path-tracing technologies like Nvidia's OptiX.
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    Real-Time Analytic Antialiased Text for 3-D Environments
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Ellis, Apollo; Hunt, Warren; Hart, John; Steinberger, Markus and Foley, Tim
    Text is a crucial component of 3-D environments and virtual worlds for user interfaces and wayfinding. Implementing text using standard antialiased texture mapping leads to blurry and illegible writing which hinders usability and navigation. While supersampling removes some of these artifacts, distracting artifacts can still impede legibility, especially for recent high-resolution head-mounted displays. We propose an analytic antialiasing technique that efficiently computes the coverage of text glyphs, over pixel footprints, designed to run at real-time rates. It decomposes glyphs into piecewise-biquadratics and trapezoids that can be quickly area-integrated over a pixel footprint to provide crisp legible antialiased text, even when mapped onto an arbitrary surface in a 3-D virtual environment.
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    Distortion-Free Displacement Mapping
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Zirr, Tobias; Ritschel, Tobias; Steinberger, Markus and Foley, Tim
    Displacement mapping is routinely used to add geometric details in a fast and easy-to-control way, both in offline rendering as well as recently in interactive applications such as games. However, it went largely unnoticed (with the exception of McGuire and Whitson [MW08]) that, when applying displacement mapping to a surface with a low-distortion parametrization, this parametrization is distorted as the geometry was changed by the displacement mapping. Typical resulting artifacts are ''rubber band''-like distortion patterns in areas of strong displacement change where a small isotropic area in texture space is mapped to a large anisotropic area in world space. We describe a fast, fully GPU-based two-step procedure to resolve this problem. First, a correction deformation is computed from the displacement map. Second, two variants to apply this correction when computing displacement mapping are proposed. The first variant is backward-compatible and can resolve the artifact in any rendering pipeline without modifying it and without requiring additional computation at render time, but only works for bijective parametrizations. The second variant works for more general parametrizations, but requires to modify the rendering code and incurs a very small computational overhead.
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    An Efficient Solution to Structured Optimization Problems using Recursive Matrices
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Rückert, Darius; Stamminger, Marc; Steinberger, Markus and Foley, Tim
    We present a linear algebra framework for structured matrices and general optimization problems. The matrices and matrix operations are defined recursively to efficiently capture complex structures and enable advanced compiler optimization. In addition to common dense and sparse matrix types, we define mixed matrices, which allow every element to be of a different type. Using mixed matrices, the low- and high-level structure of complex optimization problems can be encoded in a single type. This type is then analyzed at compile time by a recursive linear solver that picks the optimal algorithm for the given problem. For common computer vision problems, our system yields a speedup of 3-5 compared to other optimization frameworks. The BLAS performance is benchmarked against the MKL library. We achieve a significant speedup in block-SPMV and block-SPMM. This work is implemented and released open-source as a header-only extension to the C++ math library Eigen.
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    High-Performance Graphics 2019 - CGF38-8: Frontmatter
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Steinberger, Markus; Foley, Tim; Steinberger, Markus and Foley, Tim