Hansong Zhang

Visibility culling using hierarchical occlusion maps

We present hierarchical occlusion maps (HOM) for visibility culling on complex models with high depth complexity. The culling algorithm uses an object space bounding volume hierarchy and a hierarchy of image space occlusion maps. Occlusion maps represent the aggregate of projections of the occluders onto the image plane. For each frame, the algorithm selects a small set of objects from the modelas occludersand renders them to form an initial occlusion map, from which a hierarchy of occlusion maps is built. The occlusion maps are used to cull away a portion of the model not visible from the current viewpoint. The algorithm is applicable to all models and makes no assumptions about the size, shape, or type of occluders. It supports approximate culling in which small holes in or among occluders can be ignored. The algorithm has been implemented on current graphics systems and has been applied to large models composed of hundreds of thousands of polygons. In practice, it achieves significant speedup in interactive walkthroughs of models with high depth complexity. CR

MMR: an interactive massive model rendering system using geometric and image-based acceleration

We present a system for rendering very complex 3D models at interactive rates. We select a subset of the model as preferred viewpoints and partition the space into virtual cells. Each cell contains near geometry, rendered using levels of detail and visibility culling, and far geometry, rendered as a textured depth mesh. Our system automatically balances the screen-space errors resulting from geometric simplification with those from textureddepth-mesh distortion. We describe our prefetching and data management schemes, both crucial for models significantly larger than available system memory. We have successfully used our system to accelerate walkthroughs of a 13 million triangle model of a large coal-fired power plant and of a 1.7 million triangle architectural model. We demonstrate the walkthrough of a 1.3 GB power plant model with a 140 MB cache footprint.

Fast backface culling using normal masks

This paper presents a novel method for fast and efficient backface culling: we reduce the backface test to one logical operation per polygon while requiring only two bytes extra storage per polygon. The normal mask is introduced, where each bit is associated with a cluster of normals in a normal-space partitioning. A polygons normal is approximated by the cluster of normals in which it falls; the clusters normal mask is stored with the polygon in a preprocessing step. Although conceptually the normal masks require as many bits as the number of clusters, we observe that only two bytes are actually necessary. For each frame (and for each viewing volume), we calculate the backface mask by ORing the normals masks of all normal clusters that are backfacing. The backface test finally reduces to a single logical AND operation between the polygons normal mask and the backface mask. CR

Accelerated walkthrough of large spline models

CAD and rmimation applications. In this pa-per, we present algorithms for interactive walkthrough ofcomplex NURBS models composed of tens of thousands ofpatches on current graphics systems. Given a spline model,the algorithm precomputes simplification of a collection ofpatches and represents them hierarchically. Given a chang-ing viewpoint, the algorithm combines these simplificationswith dynamic tessellations to generate appropriate levels ofdetail. We also propose a system pipeline for parallel im-plementation on multi-processor configurations. Diiferentcomponents,

Efficient radiosity rendering using textures and bicubic reconstruction

Wepresenta method to speed up walkthmttghs of static scenes. It involves the cmatiort of acmttimsous C1 radiosity reconstruction for adaptively sampled tegiotts. This mpmaentation is a unitied solution to handle usuestricted quadtrees and T-vertices, and allows for the generation of multiple different levels-of-detail of the radiosity function, which are represented as texture maps. The method also involves the use of hardwase bicublc filtering for the mdiosity shading. Both techniques allow improvenmts in performance and memory usage while preserving visual appearance. CR CMegories and Subject Deaeriptom: L3.3 [Computer Graphics]: Pictusdmage Generation Viewing Algorithm, 1.3.6 [Computer Graphics]: Methodology and Techniques Integration Techniques. Additioatsl

Order of Pixel Traversal and Parallel Volume Ray-tracing on the Distributed Shared Volume Buffer

The distributed shared volume buffer (DSVB) is a software package we developed to facilitate general, parallel volume ray-tracing on networked workstations. It is internally implemented with message-passing and adopts the cache-coherent shared memory model. Thus the cache efficiency of volume data access is of utter importance to the performance of a DVSB-based ray-tracer. For a given data set, the data access behavior of a volume ray-tracer depends mostly on the way in which pixels of the image are traversed. This paper addresses the cache coherence problem and compares three kinds of pixel traversal order: one-way, two-way and along a space filling curve. Experiments show that traversing pixels along a space filling curve (e.g. a Hilbert curve) greatly enhances cache efficiency especially when size of the cache is small compared to that of the volume data, and in the meantime greatly simplifies task distribution and management.

A derivation of image-based rendering for conventional three-dimensional graphics

Abstract Image-based rendering generates images from one or more known images without explicit geometric representation of objects. This paper presents a derivation of the pixel transformations for three-dimensional image warping, a popular form of image-based rendering. The derivation is based entirely on traditional three-dimensional graphics terminology, using only 4 × 4 matrices. The transformations are optimized based on the fact that transformations of adjacent pixels share much common computation. Derivatives and frame-to-frame coherence are also discussed.

Pattern generation with color map Gouraud shading

Abstract This paper introduces a simple and fast method for generating intricate and aesthetically pleasing patterns. The essence of the method is rendering color map Gouraud-shaded polygons. In color map Gouraud shading, the interpolated values are not the RGB color components but the indices of entries in a color map. The method can produce a great variety of complex patterns, and the generation time depends almost solely on the speed of rendering Gouraud-shaded polygons.