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Item Freeform Shadow Boundary Editing(The Eurographics Association and Blackwell Publishing Ltd., 2013) Mattausch, Oliver; Igarashi, Takeo; Wimmer, Michael; I. Navazo, P. PoulinWe present an algorithm for artistically modifying physically based shadows. With our tool, an artist can directly edit the shadow boundaries in the scene in an intuitive fashion similar to freeform curve editing. Our algorithm then makes these shadow edits consistent with respect to varying light directions and scene configurations, by creating a shadow mesh from the new silhouettes. The shadow mesh helps a modified shadow volume algorithm cast shadows that conform to the artistic shadow boundary edits, while providing plausible interaction with dynamic environments, including animation of both characters and light sources. Our algorithm provides significantly more fine-grained local and direct control than previous artistic light editing methods, which makes it simple to adjust the shadows in a scene to reach a particular effect, or to create interesting shadow shapes and shadow animations. All cases are handled with a single intuitive interface, be it soft shadows, or (self-)shadows on arbitrary receivers.Item Practical Spectral Photography(The Eurographics Association and John Wiley and Sons Ltd., 2012) Habel, Ralf; Kudenov, Michael; Wimmer, Michael; P. Cignoni and T. ErtlWe introduce a low-cost and compact spectral imaging camera design based on unmodified consumer cameras and a custom camera objective. The device can be used in a high-resolution configuration that measures the spectrum of a column of an imaged scene with up to 0.8 nm spectral resolution, rivalling commercial non-imaging spectrometers, and a mid-resolution hyperspectral mode that allows the spectral measurement of a whole image, with up to 5 nm spectral resolution and 120x120 spatial resolution. We develop the necessary calibration methods based on halogen/fluorescent lamps and laser pointers to acquire all necessary information about the optical system. We also derive the mathematical methods to interpret and reconstruct spectra directly from the Bayer array images of a standard RGGB camera. This objective design introduces accurate spectral remote sensing to computational photography, with numerous applications in color theory, colorimetry, vision and rendering, making the acquisition of a spectral image as simple as taking a high-dynamic-range image.Item Efficient Spherical Harmonics Lighting with the Preetham Skylight Model(The Eurographics Association, 2008) Habel, Ralf; Mustata, Bogdan; Wimmer, Michael; Katerina Mania and Eric ReinhardWe present a fast and compact representation of a skylight model for spherical harmonics lighting, especially for outdoor scenes. This representation allows dynamically changing the sun position and weather conditions on a per frame basis. We chose the most used model in real-time graphics, the Preetham skylight model, because it can deliver both realistic colors and dynamic range and its extension into spherical harmonics can be used to realistically light a scene. We separate the parameters of the Preetham skylight model s spherical harmonics extension and perform a polynomial two-dimensional non-linear least squares fit for the principal parameters to achieve both negligible memory and computation costs. Additionally, we execute a domain specific Gibbs phenomena suppression to remove ringing artifacts.Item CHC+RT: Coherent Hierarchical Culling for Ray Tracing(The Eurographics Association and John Wiley & Sons Ltd., 2015) Mattausch, Oliver; Bittner, JirÃ; Jaspe, Alberto; Gobbetti, Enrico; Wimmer, Michael; Pajarola, Renato; Olga Sorkine-Hornung and Michael WimmerWe propose a new technique for in-core and out-of-core GPU ray tracing using a generalization of hierarchical occlusion culling in the style of the CHC++ method. Our method exploits the rasterization pipeline and hardware occlusion queries in order to create coherent batches of work for localized shader-based ray tracing kernels. By combining hierarchies in both ray space and object space, the method is able to share intermediate traversal results among multiple rays. We exploit temporal coherence among similar ray sets between frames and also within the given frame. A suitable management of the current visibility state makes it possible to benefit from occlusion culling for less coherent ray types like diffuse reflections. Since large scenes are still a challenge for modern GPU ray tracers, our method is most useful for scenes with medium to high complexity, especially since our method inherently supports ray tracing highly complex scenes that do not fit in GPU memory. For in-core scenes our method is comparable to CUDA ray tracing and performs up to 5:94 better than pure shader-based ray tracing.Item Layer-Based Procedural Design of Façades(The Eurographics Association and John Wiley & Sons Ltd., 2015) IlcÃk, Martin; Musialski, Przemyslaw; Auzinger, Thomas; Wimmer, Michael; Olga Sorkine-Hornung and Michael WimmerWe present a novel procedural framework for interactively modeling building façades. Common procedural approaches, such as shape grammars, assume that building façades are organized in a tree structure, while in practice this is often not the case. Consequently, the complexity of their layout description becomes unmanageable for interactive editing. In contrast, we obtain a façade by composing multiple overlapping layers, where each layer contains a single rectilinear grid of façade elements described by two simple generator patterns. This way, the design process becomes more intuitive and the editing effort for complex layouts is significantly reduced. To achieve this, we present a method for the automated merging of different layers in the form of a mixed discrete and continuous optimization problem. Finally, we provide several modeling examples and a comparison to shape grammars in order to highlight the advantages of our method when designing realistic building façades.Item Teaching a Modern Graphics Pipeline Using a Shader-based Software Renderer(The Eurographics Association, 2012) Fink, Heinrich; Weber, Thomas; Wimmer, Michael; Giovanni Gallo and Beatriz Sousa SantosShaders are a fundamental pattern of the modern graphics pipeline. This paper presents a syllabus for an introductory computer graphics course that emphasizes the use of programmable shaders while teaching raster-level algorithms at the same time. We describe a Java-based framework that is used for programming assignments in this course. This framework implements a shader-enabled software renderer and an interactive 3D editor. We also show how to create attractive course materials by using COLLADA, an open standard for 3D content exchange.Item The Road to Vulkan: Teaching Modern Low-Level APIs in Introductory Graphics Courses(The Eurographics Association, 2022) Unterguggenberger, Johannes; Kerbl, Bernhard; Wimmer, Michael; Bourdin, Jean-Jacques; Paquette, EricFor over two decades, the OpenGL API provided users with the means for implementing versatile, feature-rich, and portable real-time graphics applications. Consequently, it has been widely adopted by practitioners and educators alike and is deeply ingrained in many curricula that teach real-time graphics for higher education. Over the years, the architecture of graphics processing units (GPUs) incrementally diverged from OpenGL's conceptual design. The more recently introduced Vulkan API provides a more modern, fine-grained approach for interfacing with the GPU. Various properties of this API and overall trends suggest that Vulkan could soon replace OpenGL in many areas. Hence, it stands to reason that educators who have their students' best interests at heart should provide them with corresponding lecture material. However, Vulkan is notoriously verbose and rather challenging for first-time users, thus transitioning to this new API bears a considerable risk of failing to achieve expected teaching goals. In this paper, we document our experiences after teaching Vulkan in an introductory graphics course side-by-side with conventional OpenGL. A final survey enables us to draw conclusions about perceived workload, difficulty, and students' acceptance of either approach and identify suitable conditions and recommendations for teaching Vulkan to undergraduate students.Item Analytic Visibility on the GPU(The Eurographics Association and Blackwell Publishing Ltd., 2013) Auzinger, Thomas; Wimmer, Michael; Jeschke, Stefan; I. Navazo, P. PoulinThis paper presents a parallel, implementation-friendly analytic visibility method for triangular meshes. Together with an analytic filter convolution, it allows for a fully analytic solution to anti-aliased 3D mesh rendering on parallel hardware. Building on recent works in computational geometry, we present a new edge-triangle intersection algorithm and a novel method to complete the boundaries of all visible triangle regions after a hidden line elimination step. All stages of the method are embarrassingly parallel and easily implementable on parallel hardware. A GPU implementation is discussed and performance characteristics of the method are shown and compared to traditional sampling-based rendering methods.Item Automatic Generation of Tourist Brochures(The Eurographics Association and John Wiley and Sons Ltd., 2014) Birsak, Michael; Musialski, Przemyslaw; Wonka, Peter; Wimmer, Michael; B. Levy and J. KautzWe present a novel framework for the automatic generation of tourist brochures that include routing instructions and additional information presented in the form of so-called detail lenses. The first contribution of this paper is the automatic creation of layouts for the brochures. Our approach is based on the minimization of an energy function that combines multiple goals: positioning of the lenses as close as possible to the corresponding region shown in an overview map, keeping the number of lenses low, and an efficient numbering of the lenses. The second contribution is a route-aware simplification of the graph of streets used for traveling between the points of interest (POIs). This is done by reducing the graph consisting of all shortest paths through the minimization of an energy function. The output is a subset of street segments that enable traveling between all the POIs without considerable detours, while at the same time guaranteeing a clutter-free visualization.Item A Survey on Temporal Coherence Methods in Real-Time Rendering(The Eurographics Association, 2011) Scherzer, Daniel; Yang, Lei; Mattausch, Oliver; Nehab, Diego; Sander, Pedro V.; Wimmer, Michael; Eisemann, Elmar; N. John and B. WyvillNowadays, there is a strong trend towards rendering to higher-resolution displays and at high frame rates. This development aims at delivering more detail and better accuracy, but it also comes at a significant cost. Although graphics cards continue to evolve with an ever-increasing amount of computational power, the processing gain is counteracted to a high degree by increasingly complex and sophisticated pixel computations. For real-time applications, the direct consequence is that image resolution and temporal resolution are often the first candidates to bow to the performance constraints (e.g., although full HD is possible, PS3 and XBox often render at lower resolutions). In order to achieve high-quality rendering at a lower cost, one can exploit temporal coherence (TC). The underlying observation is that a higher resolution and frame rate do not necessarily imply a much higher workload, but a larger amount of redundancy and a higher potential for amortizing rendering over several frames. In this state-of-the-art report, we investigate methods that make use of this principle and provide practical and theoretical advice on how to exploit temporal coherence for performance optimization. These methods not only allow incorporating more computationally intensive shading effects into many existing applications, but also offer exciting opportunities for extending high-end graphics applications to lower-spec consumer-level hardware. To this end, we first introduce the notion and main concepts of TC, including an overview of historical methods. We then describe a key data structure, the so-called reprojection cache, with several supporting algorithms that facilitate reusing shading information from previous frames, and finally illustrated its usefulness in various applications.