29-Issue 4

Permanent URI for this collection

https://diglib.eg.org/handle/10.2312/155

Browse

Now showing 1 - 20 of 29

A Layered Particle-Based Fluid Model for Real-Time Rendering of Water
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Bagar, Florian; Scherzer, Daniel; Wimmer, Michael
We present a physically based real-time water simulation and rendering method that brings volumetric foam to the real-time domain, significantly increasing the realism of dynamic fluids. We do this by combining a particle-based fluid model that is capable of accounting for the formation of foam with a layered rendering approach that is able to account for the volumetric properties of water and foam. Foam formation is simulated through Weber number thresholding. For rendering, we approximate the resulting water and foam volumes by storing their respective boundary surfaces in depth maps. This allows us to calculate the attenuation of light rays that pass through these volumes very efficiently. We also introduce an adaptive curvature flow filter that produces consistent fluid surfaces from particles independent of the viewing distance.
Interactive Editing of Lighting and Materials using a Bivariate BRDF Representation
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Sitthi-Amorn, Pitchaya; Romeiro, Fabiano; Zickler, Todd; Lawrence, Jason
We present a new Precomputed Radiance Transfer (PRT) algorithm based on a two dimensional representation of isotropic BRDFs. Our approach involves precomputing matrices that allow quickly mapping environment lighting, which is represented in the global coordinate system, and the surface BRDFs, which are represented in a bivariate domain, to the local hemisphere at a surface location where the reflection integral is evaluated. When the lighting and BRDFs are represented in a wavelet basis, these rotation matrices are sparse and can be efficiently stored and combined with pre-computed visibility at run-time. Compared to prior techniques that also precompute wavelet rotation matrices, our method allows full control over the lighting and materials due to the way the BRDF is represented. Furthermore, this bivariate parameterization preserves sharp specular peaks and grazing effects that are attenuated in conventional parameterizations. We demonstrate a prototype rendering system that achieves real-time framerates while lighting and materials are edited.
A PCA Decomposition for Real-time BRDF Editing and Relighting with Global Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Nguyen, Chuong H.; Kyung, Min-Ho; Lee, Joo-Haeng; Nam, Seung-Woo
We propose a novel rendering method which supports interactive BRDF editing as well as relighting on a 3D scene. For interactive BRDF editing, we linearize an analytic BRDF model with basis BRDFs obtained from a principal component analysis. For each basis BRDF, the radiance transfer is precomputed and stored in vector form. In rendering time, illumination of a point is computed by multiplying the radiance transfer vectors of the basis BRDFs by the incoming radiance from gather samples and then linearly combining the results weighted by user-controlled parameters. To improve the level of accuracy, a set of sub-area samples associated with a gather sample refines the glossy reflection of the geometric details without increasing the precomputation time. We demonstrate this program with a number of examples to verify the real-time performance of relighting and BRDF editing on 3D scenes with complex lighting and geometry.
An Optimizing Compiler for Automatic Shader Bounding
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Clarberg, Petrik; Toth, Robert; Hasselgren, Jon; Akenine-Moeller, Tomas
A New Ward BRDF Model with Bounded Albedo
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Geisler-Moroder, David; Duer, Arne
Due to its realistic appearance, computational convenience, and efficient Monte Carlo sampling, Ward s anisotropic BRDF is widely used in computer graphics for modeling specular reflection. Incorporating the criticism that the Ward and the Ward-Duer model do not meet energy balance at grazing angles, we propose a modified BRDF that is energy conserving and preserves Helmholtz reciprocity. The new BRDF is computationally cheap to evaluate, admits efficient importance sampling, and thus sustains the main benefits of the Ward model. We show that the proposed BRDF is better suited for fitting measured reflectance data of a linoleum floor used in a real-world building than the Ward and the Ward-Duer model.
Visibility Editing For All-Frequency Shadow Design
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Obert, Juraj; Pellacini, Fabio; Pattanaik, Sumanta
We present an approach for editing shadows in all-frequency lighting environments. To support artistic control, we propose to decouple shadowing from lighting and focus on providing intuitive controls to edit the former. To accomplish this task, we precompute and store scene visibility information separately from lighting and BRDFs and allow artists to edit visibility directly, by providing operations to select shadows and edit their shape. To facilitate a wider range of editing operations, we generalize visibility from binary to three-channel oating point quantities and introduce a novel shadow representation based on computation of visibility ratios between the original render and the edited one. We demonstrate our results for diffuse and glossy surfaces, still scenes and animations.
Interactive Rendering of Non-Constant, Refractive Media Using the Ray Equations of Gradient-Index Optics
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Cao, Chen; Ren, Zhong; Guo, Baining; Zhou, Kun
Existing algorithms can efficiently render refractive objects of constant refractive index. For a medium with a continuously varying index of refraction, most algorithms use the ray equation of geometric optics to compute piecewise-linear approximations of the non-linear rays. By assuming a constant refractive index within each tracing step, these methods often need a large number of small steps to generate satisfactory images. In this paper, we present a new approach for tracing non-constant, refractive media based on the ray equations of gradient-index optics. We show that in a medium of constant index gradient, the ray equation has a closed-form solution, and the intersection point between a ray and the medium boundaries can be efficiently computed using the bisection method. For general non-constant media, we model the refractive index as a piecewise-linear function and render the refraction by tracing the tetrahedron-based representation of the media. Our algorithm can be easily combined with existing rendering algorithms such as photon mapping to generate complex refractive caustics at interactive frame rates. We also derive analytic ray formulations for tracing mirages - a special gradient-index optical phenomenon.
Multi-Image Based Photon Tracing for Interactive Global Illumination of Dynamic Scenes
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Yao, Chunhui; Wang, Bin; Chan, Bin; Yong, Junhai; Paul, Jean-Claude
Image space photon mapping has the advantage of simple implementation on GPU without pre-computation of complex acceleration structures. However, existing approaches use only a single image for tracing caustic photons, so they are limited to computing only a part of the global illumination effects for very simple scenes. In this paper we fully extend the image space approach by using multiple environment maps for photon mapping computation to achieve interactive global illumination of dynamic complex scenes. The two key problems due to the introduction of multiple images are 1) selecting the images to ensure adequate scene coverage; and 2) reliably computing ray-geometry intersections with multiple images. We present effective solutions to these problems and show that, with multiple environment maps, the image-space photon mapping approach can achieve interactive global illumination of dynamic complex scenes. The advantages of the method are demonstrated by comparison with other existing interactive global illumination methods.
Invisible Seams
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Ray, Nicolas; Nivoliers, Vincent; Lefebvre, Sylvain; Levy, Bruno
Surface materials are commonly described by attributes stored in textures (for instance, color, normal, or displacement). Interpolation during texture lookup provides a continuous value field everywhere on the surface, except at the chart boundaries where visible discontinuities appear. We propose a solution to make these seams invisible, while still outputting a standard texture atlas. Our method relies on recent advances in quad remeshing using global parameterization to produce a set of texture coordinates aligning texel grids across chart boundaries. This property makes it possible to ensure that the interpolated value fields on both sides of a chart boundary precisely match, making all seams invisible. However, this requirement on the uv coordinates needs to be complemented by a set of constraints on the colors stored in the texels. We propose an algorithm solving for all the necessary constraints between texel values, including through different magnification modes (nearest, bilinear, biquadratic and bicubic), and across facets using different texture resolutions. In the typical case of bilinear magnification and uniform resolution, none of the texels appearing on the surface are constrained. Our approach also ensures perfect continuity across several MIP-mapping levels.
Fragment-Parallel Composite and Filter
(The Eurographics Association and Blackwell Publishing Ltd, 2010)
Adaptive Volumetric Shadow Maps
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Salvi, Marco; Vidimce, Kiril; Lauritzen, Andrew; Lefohn, Aaron
We introduce adaptive volumetric shadow maps (AVSM), a real-time shadow algorithm that supports high-quality shadowing from dynamic volumetric media such as hair and smoke. The key contribution of AVSM is the introduction of a streaming simplification algorithm that generates an accurate volumetric light attenuation function using a small fixed memory footprint. This compression strategy leads to high performance because the visibility data can remain in on-chip memory during simplification and can be efficiently sampled during rendering. We demonstrate that AVSM compression closely approximates the ground-truth correct solution and performs competitively to existing real-time rendering techniques while providing higher quality volumetric shadows.
On the Effective Dimension of Light Transport
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Lessig, Christian; Fiume, Eugene
Light transport is often characterized within a high-dimensional space although practitioners have long known that it commonly behaves as a much lower-dimensional phenomenon. We study the effective dimension of light transport over a neighborhood on the scene manifold and show that under plausible assumptions the dimensionality is characterized by the spectrum of the spatio-spectral concentration problem. This allows us to improve existing estimates for the dimension in computer graphics using a more insightful derivation and for the first time we obtain optimal representations. The relevance of our results for existing rendering applications is discussed.
On Floating-Point Normal Vectors
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Meyer, Quirin; Suessmuth, Jochen; Sussner, Gerd; Stamminger, Marc; Greiner, Guenther
In this paper we analyze normal vector representations. We derive the error of the most widely used representation, namely 3D floating-point normal vectors. Based on this analysis, we show that, in theory, the discretization error inherent to single precision floating-point normals can be achieved by 250.2 uniformly distributed normals, addressable by 51 bits. We review common sphere parameterizations and show that octahedron normal vectors perform best: they are fast and stable to compute, have a controllable error, and require only 1 bit more than the theoretical optimal discretization with the same error.
Two Methods for Fast Ray-Cast Ambient Occlusion
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Laine, Samuli; Karras, Tero
Ambient occlusion has proven to be a useful tool for producing realistic images, both in offline rendering and interactive applications. In production rendering, ambient occlusion is typically computed by casting a large number of short shadow rays from each visible point, yielding unparalleled quality but long rendering times. Interactive applications typically use screen-space approximations which are fast but suffer from systematic errors due to missing information behind the nearest depth layer.In this paper, we present two efficient methods for calculating ambient occlusion so that the results match those produced by a ray tracer. The first method is targeted for rasterization-based engines, and it leverages the GPU graphics pipeline for finding occlusion relations between scene triangles and the visible points. The second method is a drop-in replacement for ambient occlusion computation in offline renderers, allowing the querying of ambient occlusion for any point in the scene. Both methods are based on the principle of simultaneously computing the result of all shadow rays for a single receiver point.
Interactive, Multiresolution Image-Space Rendering for Dynamic Area Lighting
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Nichols, Greg; Penmatsa, Rajeev; Wyman, Chris
Area lights add tremendous realism, but rendering them interactively proves challenging. Integrating visibility is costly, even with current shadowing techniques, and existing methods frequently ignore illumination variations at unoccluded points due to changing radiance over the light s surface. We extend recent image-space work that reduces costs by gathering illumination in a multiresolution fashion, rendering varying frequencies at corresponding resolutions. To compute visibility, we eschew shadow maps and instead rely on a coarse screen-space voxelization, which effectively provides a cheap layered depth image for binary visibility queries via ray marching. Our technique requires no precomputation and runs at interactive rates, allowing scenes with large area lights, including dynamic content such as video screens.
Fast Estimation and Rendering of Indirect Highlights
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Laurijssen, J.; Wang, R.; Dutre, Ph.; Brown, B.J.
This paper proposes a method for efficiently rendering indirect highlights. Indirect highlights are caused by the primary light source reflecting off two or more glossy surfaces. Accurately simulating such highlights is important to convey the realistic appearance of materials such as chrome and shiny metal. Our method models the glossy BRDF at a surface point as a directional distribution, using a spherical von Mises-Fisher (vMF) distribution. As our main contribution, we merge multiple vMFs into a combined multimodal distribution. This effectively creates a filtered radiance response function, allowing us to efficiently estimate indirect highlights. We demonstrate our method in a near-interactive application for rendering scenes with highly glossy objects. Our results produce realistic reflections under both local and environment lighting.
A Closed-Form Solution to Single Scattering for General Phase Functions and Light Distributions
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Pegoraro, Vincent; Schott, Mathias; Parker, Steven G.
Due to the intricate nature of the equation governing light transport in participating media, accurately and efficiently simulating radiative energy transfer remains very challenging in spite of its broad range of applications. As an alternative to traditional numerical estimation methods such as ray-marching and volume-slicing, a few analytical approaches to solving single scattering have been proposed but current techniques are limited to the assumption of isotropy, rely on simplifying approximations and/or require substantial numerical precomputation and storage. In this paper, we present the very first closed-form solution to the air-light integral in homogeneous media for general 1-D anisotropic phase functions and punctual light sources. By addressing an open problem in the overall light transport literature, this novel theoretical result enables the analytical computation of exact solutions to complex scattering phenomena while achieving semi-interactive performance on graphics hardware for several common scattering modes.
Semi-Stochastic Tilings for Example-Based Texture Synthesis
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Schloemer, Thomas; Deussen, Oliver
We investigate semi-stochastic tilings based on Wang or corner tiles for the real-time synthesis of example-based textures. In particular, we propose two new tiling approaches: (1) to replace stochastic tilings with pseudo-random tilings based on the Halton low-discrepancy sequence, and (2) to allow the controllable generation of tilings based on a user-provided probability distribution. Our first method prevents local repetition of texture content as common with stochastic approaches and yields better results with smaller sets of utilized tiles. Our second method allows to directly influence the synthesis result which-in combination with an enhanced tile construction method that merges multiple source textures-extends synthesis tasks to globally-varying textures. We show that both methods can be implemented very efficiently in connection with tile-based texture mapping and also present a general rule that allows to significantly reduce resulting tile sets.
BendyLights: Artistic Control of Direct Illumination by Curving Light Rays
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Kerr, William B.; Pellacini, Fabio; Denning, Jonathan D.
In computer cinematography, artists routinely use non-physical lighting models to achieve desired appearances. This paper presents BendyLights, a non-physical lighting model where light travels nonlinearly along splines, allowing artists to control light direction and shadow position at different points in the scene independently. Since the light deformation is smoothly defined at all world-space positions, the resulting non-physical lighting effects remain spatially consistent, avoiding the frequent incongruences of many non-physical models. BendyLights are controlled simply by reshaping splines, using familiar interfaces, and require very few parameters. BendyLight control points can be keyframed to support animated lighting effects. We demonstrate BendyLights both in a realtime rendering system for editing and a production renderer for final rendering, where we show that BendyLights can also be used with global illumination.
Grammar-based Encoding of Facades
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Haegler, Simon; Wonka, Peter; Arisona, Stefan Mueller; Van Gool, Luc; Mueller, Pascal
In this paper we propose a real-time rendering approach for procedural cities. Our first contribution is a new lightweight grammar representation that compactly encodes facade structures and allows fast per-pixel access. We call this grammar F-shade. Our second contribution is a prototype rendering system that renders an urban model from the compact representation directly on the GPU. Our suggested approach explores an interesting connection from procedural modeling to real-time rendering. Evaluating procedural descriptions at render time uses less memory than the generation of intermediate geometry. This enables us to render large urban models directly from GPU memory.

Browse

Browsing 29-Issue 4 by Issue Date

Results Per Page

Sort Options