Wolfgang Straßer

Real time compression of triangle mesh connectivity

In this paper we introduce a new compressed representation for the connectivity of a triangle mesh. We present local compression and decompression algorithms which are fast enough for real time applications. The achieved space compression rates keep pace with the best rates reported for any known global compression algorithm. These nice properties have great benefits for several important applications. Naturally, the technique can be used to compress triangle meshes without significant delay before they are stored on external devices or transmitted over a network. The presented decompression algorithm is very simple allowing a possible hardware realization of the decompression algorithm which could significantly increase the rendering speed of pipelined graphics hardware. CR Categories: I.3.1 [Computer Graphics]: Hardware Architecture; I.3.3 [Computer Graphics]: Picture/Image Generation— Display algorithms

The randomized z-buffer algorithm: interactive rendering of highly complex scenes

We present a new output-sensitive rendering algorithm, the randomized z-buffer algorithm. It renders an image of an arbitrary three-dimensional scene consisting of triangular primitives by reconstruction from a dynamically chosen set of random surface sample points. This approach is independent of mesh connectivity and topology. The resulting rendering time grows only logarithmically with the numbers of triangles in the scene. We were able to render walkthroughs of scenes of up to 1014 triangles at interactive frame rates. Automatic identification of low detail scene components ensures that the rendering speed of the randomized z-buffer cannot drop below that of conventional z-buffer rendering. Experimental and analytical evidence is given that the image quality is comparable to that of common approaches like z-buffer rendering. The precomputed data structures employed by the randomized z-buffer allow for interactive dynamic updates of the scene. Their memory requirements grow only linearly with the number of triangles and allow for a scene graph based instantiation scheme to further reduce memory consumption.

Continuum‐based Strain Limiting

We present Continuum‐based Strain Limiting (CSL) – a new method for limiting deformations in physically‐based cloth simulations. Despite recent developments for nearly inextensible materials, the efficient simulation of general biphasic textiles and their anisotropic behavior remains challenging. Many approaches use soft materials and enforce limits on edge elongations, leading to discretization‐dependent behavior. Moreover, they offer no explicit control over shearing and stretching unless specifically aligned meshes are used. Based on a continuum deformation measure, our method allows accurate control over all strain components using individual thresholds. We impose deformation limits element‐wise and cast the problem as a 6×6 system of linear equations. CSL can be combined with any cloth simulator and, as a velocity filter, integrates seamlessly into standard collision handling.

Fast and Scalable CPU/GPU Collision Detection for Rigid and Deformable Surfaces

We present a new hybrid CPU/GPU collision detection technique for rigid and deformable objects based on spatial subdivision. Our approach efficiently exploits the massive computational capabilities of modern CPUs and GPUs commonly found in off‐the‐shelf computer systems. The algorithm is specifically tailored to be highly scalable on both the CPU and the GPU sides. We can compute discrete and continuous external and self‐collisions of non‐penetrating rigid and deformable objects consisting of many tens of thousands of triangles in a few milliseconds on a modern PC. Our approach is orders of magnitude faster than earlier CPU‐based approaches and up to twice as fast as the most recent GPU‐based techniques.

Terrain sketching

Procedural methods for terrain synthesis are capable of creating realistic depictions of heightfield terrains with little user intervention. However, users often do wish to intervene in controlling the placement and shape of landforms, but without sacrificing realism. In this paper, we present a sketching interface to procedural terrain generation. This system enables users to draw the silhouette, spine and bounding curves of both extruding (hills and mountains) and embedding landforms (river courses and canyons). Terrain is interactively generated to match the sketched constraints using multiresolution surface deformation. In addition, the wavelet noise characteristics of silhouette strokes are propagated to the surrounding terrain. With terrain sketching users can interactively create or modify landscapes incorporating varied and complex land-forms.

Bayesian Point Cloud Reconstruction

In this paper, we propose a novel surface reconstruction technique based on Bayesian statistics: The measurement process as well as prior assumptions on the measured objects are modeled as probability distributions and Bayes’ rule is used to infer a reconstruction of maximum probability. The key idea of this paper is to define both measurements and reconstructions as point clouds and describe all statistical assumptions in terms of this finite dimensional representation. This yields a discretization of the problem that can be solved using numerical optimization techniques. The resulting algorithm reconstructs both topology and geometry in form of a well‐sampled point cloud with noise removed. In a final step, this representation is then converted into a triangle mesh. The proposed approach is conceptually simple and easy to extend. We apply the approach to reconstruct piecewise‐smooth surfaces with sharp features and examine the performance of the algorithm on different synthetic and real‐world data sets.

Hardware for superior texture performance

Abstract Mapping textures onto surfaces of computer-generated objects is a technique which greatly improves the realism of their appearance. Unfortunately, this imposes high computational demands and, even worse, tremendous memory bandwidth requirements on the graphics system. Tight cost frames in the industry in conjunction with ever increasing user expectations make the design of a powerful texture mapping unit a difficult task. To meet these requirements we follow two different approaches. On the technology side, we observe a rapidly emerging technology which offers the combination of enormous transfer rates and computing power: logic-embedded memories. On the algorithmic side, a common way to reduce data traffic is image compression. Its application to texture mapping, however, is difficult since the decompression must be done at pixel frequency. In this work we will focus on the latter approach, describing the use of a specific compression scheme for texture mapping. It allows the use of a very simple and fast decompression hardware, bringing high performance texture mapping to low-cost systems.

A consistent bending model for cloth simulation with corotational subdivision finite elements

Wrinkles and folds play an important role in the appearance of real textiles. The way in which they form depends mainly on the bending properties of the specific material type. Existing approaches fail to reliably reproduce characteristic behaviour like folding and buckling for different material types or resolutions. It is therefore crucial for the realistic simulation of cloth to model bending energy in a physically accurate and consistent way. In this paper we present a new method based on a corotational formulation of subdivision finite elements. Due to the non-local nature of the employed subdivision basis functions a C1-continuous displacement field can be defined. In this way, it is possible to use the governing equations of thin shell analysis leading to physically accurate bending behaviour. Using a corotated strain tensor allows the large displacement analysis of cloth while retaining a linear system of equations. Hence, known convergence properties and computational efficiency are preserved while convincing and detailed folding behaviour is obtained in the simualtion.

A compact volume rendering accelerator

We describe the architecture of a hardware accelerator for volume rendering. The system basically consists of four VLSI chips and the volume memory and represents a singleboard solution to the computational challenges of volume visualization. It generates arbitrary perspective projections, so that walk-through examinations are possible. The classification of structures of interest is an integral part of the rendering pipeline. Image quality is enhanced by providing Phong shading, depth-cueing and support for translucency. Despite its compactness and algorithmic complexity, the system is able to render 2563 data sets at a sustained frame generation rate of about 2.5Hz. CR

Real-Time Caustics

We present a new algorithm to render caustics. The algorithm discretizes the specular surfaces into samplepoints. Each of the sample points is treated as a pinhole camera that projects an image of the incoming lightonto the diffuse receiver surfaces. Anti‐aliasing is performed by considering the local surface curvature at thesample points to filter the projected images. The algorithm can be implemented using programmable texturemapping hardware. It allows to render caustics in fully dynamic scenes in real‐time on current PC hardware.