Michael Meißner

OpenGL-assisted occlusion culling for large polygonal models

Abstract We present an OpenGL-assisted visibility culling algorithm to improve the rendering performance of large polygonal models. Using a combination of hierarchical model-space partitioning, OpenGL-assisted view-frustum culling, and OpenGL-assisted occlusion culling, we achieve a significantly better performance on general polygonal models than previous approaches. In contrast to these approaches, we only exploit common OpenGL features and therefore, our algorithm is also well suited for low-end OpenGL graphics hardware. Furthermore, we propose a small addition to the OpenGL rendering pipeline to enhance the framebuffers ability for faster and more detailed occlusion queries.

Extending graphics hardware for occlusion queries in OpenGL

For interactive rendering of large polygonal objects, fast visibility queries are necessary to quickly decide whether polygonal objects are visible and need to be rendered. None of the numerous published algorithms provide visibility performance for interactive rendering of large models. In this paper, we propose an OpenGL extension for fast occlusion queries. Added after the depth test stage of the OpenGL rendering pipeline, our algorithm provides fast queries to establish the occlusion of polygonal objects. Furthermore, hardware aspects of this proposal are discussed and possible implementations on two different graphics architectures are presented.

VIZARD II: a reconfigurable interactive volume rendering system

This paper presents a reconfigurable, hardware accelerated, volume rendering system for high quality perspective ray casting. The volume rendering accelerator performs ray casting by calculating the path of the ray through the volume using a programmable Xilinx Virtex FPGA which provides fast design changes and low cost development. Volume datasets are stored on the card in low profile DIMMs with standard connectors allowing both, large datasets up to 1 GByte with 32 bit per voxel, and easy upgrades to larger memory capacities. Per-sample Phong shading and post-classification is performed in hardware, giving immediate feedback to changes in the visualization of a dataset. Adding new features, such as pre-integrated classification, can be accomplished using the existing card without expensive and time consuming redesigns. The card can also be used for medical image reconstruction by reconfiguring the FPGA broadening its usefulness for end users. For the first time, users are able to generate high quality perspective images as required for applications such as virtual endoscopy and colonoscopy, and stereoscopic image generation.

Visibility Driven Rasterization

We present a new visibility driven rasterization scheme that significantly increases the rendering performance of modern graphic subsystems. Instead of rasterizing, texturing, lighting, and depth‐testing each individual pixel, we introduce a two‐level visibility mask within the rasterization stage which facilitates the removal of groups of pixels and triangles from rasterization and subsequent pipeline stages.

Voxels versus Polygons: A Comparative Approach for Volume Graphics

Different Direct Volume Rendering techniques (DVR) are introduced in the literature. The most important is the Ray Casting (RC) approach [1–2], the forward projection approach [3–4], the splatting algorithm [5], and the 3D texture mapping based projection technique [6]. In this chapter, we focus on the RC approach, since it is so far the only approach which enables adjustable sampling in all dimensions, perspective projections, and gray-level gradients. Although there are several improvements for splatting [7–8] and for texture mapping-based volume rendering [9], the overall quality and generality is not yet comparable to RC.

A low-cost memory architecture for PCI-based interactive ray casting

In this paper we present a low-cost memory architecture running at 100 MHz which is suited for any PCI-based volume rendering accelerator using the ray-casting approach. Current SDRAM technology, parallel access to all voxels required for trilinear interpolation, a cubic addressing scheme, and a buffering mechanism accommodating memory latency are applied to achieve high frame-rates. A total of four off-the-shelf standard DIMM modules are required enabling up to 9 Hz (averaged over a representative set of views) for datasets of 256 voxels, using early ray termination as the only algorithmic optimization. The presented memory architecture is a good balance of cost versus feasibility on a standard PCI card accepting data replication and will be used for the VIZARD II ray casting accelerator. CR Categories: B.3.2 [Memory Structures]: Design Style, Associative and Cache Memories; I.3.1 [Computer Graphics]: Hardware Architecture, Graphics Processors; I.3.3 [Computer Graphics]: Picture/Image Generation, Display Algorithms

Implementations of Cube-4 on the Teramac custom computing machine

Abstract We present two implementations of the Cube-4 volume rendering architecture, developed at SUNY Stony Brook, on the Teramac custom computing machine. Cube-4 uses a slice-parallel ray-casting algorithm that allows for a parallel and pipelined implementation of ray-casting. Tri-linear interpolation, surface normal estimation from interpolated samples, shading, classification, and compositing are part of the rendering pipeline. Using the partitioning schemes introduced in this paper, Cube-4 is capable of rendering in real-time large datasets (e.g., 10243) with a limited number of rendering pipelines. Teramac is a hardware simulator developed at Hewlett-Packard Research Laboratories. Teramac belongs to the new class of custom computing machines, which combine the speed of special-purpose hardware with the flexibility of general-purpose computers. Using Teramac as a development tool, we implemented two working Cube-4 prototypes capable of rendering 1283 datasets in 0.65 s at a very low 0.96 MHz processing frequency. The results from these implementations indicate scalable performance with the number of rendering pipelines and real-time frame-rates for high-resolution datasets.

Translucent and opaque direct volume rendering for virtual endoscopy applications

Virtual endoscopy applications frequently require the visual representation of several material interfaces to show the relevant data feature to the user. This requires the specification of complex transfer function which classify the various materials and color them appropriately. In this paper, we explore the use of the direct volume rendering for virtual endoscopy. We specifically look into the visual representation of different anatomical features of various volume datasets, which are located below the inner surface of the organ of interest. Furthermore, we present how interactivity can be accomplished with the VIZARD II ray casting accelerator board.

Efficient space leaping for ray casting architectures

One of the most severe problems for ray casting architectures is the waste of computation cycles and I/O bandwidth, due to redundant sampling of empty space. While several techniques exist for software implementations to skip these empty regions, few are suitable for hardware implementation. The few which have been presented either require a tremendous amount of logic or are not feasible for high frequency designs (i.e. running at 100 MHz) where latency is the one of the biggest issues. In this paper, we present an efficient space leaping mechanism which requires only a small amount of SRAM (4 Kbit for a 2563 volume) and can be easily integrated into ray casting architectures. For each sub-cube of the volume, a bit is stored in an occupancy map, which can be generated in real-time, using the VIZARD II architecture. Hence, space leaping can be classification dependent achieving yet another significant speed-up over skipping only the empty space (voxel = 0). Using a set of real-world datasets, we show that frame-rates well above 15 frames per second can be accomplished for the VIZARD II architecture.

VIZARD II: An FPGA-based Interactive Volume Rendering System

In this paper we present a volume rendering system that implements a Direct Volume Rendering algorithm on a Xilinx FPGA being capable of visualizing 3D-datasets with highest image quality at interactive frame rate. The volume renderer utilizes a cache optimized memory scheme for maximum memory bandwidth and a fully pipelined architecture of the computational expensive rendering calculations. The used ray-casting algorithm was adapted in critical parts to fit the specific need of an efficient hardware usage, with respect to available resources and computational power, without limiting rendering features.Using a FPGA approach offers full flexibility to the implementation of the algorithm making it easy to adapt and extend new features to the rendering pipeline without the need of time consuming redesigns, especially important in a scientific environment.