The rapid increase in the performance of graphics hardware, coupled with recent improvements in its programmability, have made graphics hardware a compelling platform for computationally demanding tasks in a wide variety of application domains. In this report, we describe, summarize, and analyze the latest research in mapping general-purpose computation to graphics hardware. We begin with the technical motivations that underlie general-purpose computation on graphics processors (GPGPU) and describe the hardware and software developments that have led to the recent interest in this field. We then aim the main body of this report at two separate audiences. First, we describe the techniques used in mapping general-purpose computation to graphics hardware. We believe these techniques will be generally useful for researchers who plan to develop the next generation of GPGPU algorithms and techniques. Second, we survey and categorize the latest developments in general-purpose application development on graphics hardware. This survey should be of particular interest to researchers who are interested in using the latest GPGPU applications in their systems of interest.

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A Survey of General-Purpose Computation on Graphics Hardware

A Survey of General-Purpose Computation on Graphics Hardware.

The tremendous evolution of programmable graphics hardware has made high-quality real-time volume graphics a reality. In addition to the traditional application of rendering volume data in scientific visualization, the interest in applying these techniques for real-time rendering of atmospheric phenomena and participating media such as fire, smoke, and clouds is growing rapidly. This course covers both applications in scientific visualization, e.g., medical volume data, and real-time rendering, such as advanced effects and illumination in computer games, in detail. Course participants will learn techniques for harnessing the power of consumer graphics hardware and high-level shading languages for real-time rendering of volumetric data and effects. Beginning with basic texture-based approaches including hardware ray casting, the algorithms are improved and expanded incrementally, covering local and global illumination, scattering, pre-integration, implicit surfaces and non-polygonal isosurfaces, transfer function design, volume animation and deformation, dealing with large volumes, high-quality volume clipping, rendering segmented volumes, higher-order filtering, and non-photorealistic volume rendering. Course participants are provided with documented source code covering details usually omitted in publications.

Real-Time Volume Graphics

Morphogenesis emerges from complex multiscale interactions between genetic and mechanical processes. To understand these processes, the evolution of cell shape, proliferation and gene expression must be quantified. This quantification is usually performed either in full 3D, which is computationally expensive and technically challenging, or on 2D planar projections, which introduces geometrical artifacts on highly curved organs. Here we present MorphoGraphX ( www.MorphoGraphX.org), a software that bridges this gap by working directly with curved surface images extracted from 3D data. In addition to traditional 3D image analysis, we have developed algorithms to operate on curved surfaces, such as cell segmentation, lineage tracking and fluorescence signal quantification. The software's modular design makes it easy to include existing libraries, or to implement new algorithms. Cell geometries extracted with MorphoGraphX can be exported and used as templates for simulation models, providing a powerful platform to investigate the interactions between shape, genes and growth.

https://cdn.elifesciences.org/articles/05864/elife-05864-v1.pdf

MorphoGraphX: A platform for quantifying morphogenesis in 4D

A graphics processing system includes a graphics processor and a memory for storing data to be used by and generated by the graphics processor. In a first rendering pass, the graphics processor generates an array of graphics data and stores the generated array of graphics data in the memory. The array of graphics data generated in the first rendering pass is used in a subsequent rendering pass. In the first rendering pass, the graphics processor determines one or more regions of the array of graphics data that have a particular characteristic, and generates information indicative of the one or more regions. In the subsequent rendering pass, the graphics processor uses the information indicative of the one or more regions to control the reading of the array of graphics data when it is to be used in the subsequent rendering pass.

Graphics processing systems

Correctly rendering non-refractive transparent surfaces with core OpenGL functionality [9] has the vexing requirements of depth-sorted traversal and nonintersecting polygons. This is frustrating for most application developers using OpenGL because the natural order of scene traversal (usually one object at a time) rarely satisfies these requirements. Objects can be complex, with their own transformation hierarchies. Even more troublesome, with advanced graphics hardware, the vertices and fragments of objects may be altered by user-defined per-vertex or per-fragment operations within the GPU. When these features are employed, it becomes intractable to guarantee that fragments will arrive in sorted order for each pixel. The technique presented here solves the problem of order dependence by using a technique we call depth peeling. Depth peeling is a fragment-level depth sorting technique described by Mammen using Virtual Pixel Maps [7] and by Diefenbach using a dual depth buffer [3]. Though no dual depth buffer hardware fitting Diefenbach’s description exists, Bastos observed that shadow mapping hardware in conjunction with alpha test can be used to achieve the same effect [2]. Using this variation of depth peeling, each unique depth in the scene is extracted into layers, and the layers are composited in depth-sorted order to produce the correctly blended final image. The peeling of a layer requires a single order-independent pass over the scene. Figure 1 contrasts correct and incorrect rendering of transparent surfaces. (a) (b)

https://gamedevs.org/uploads/interactive-order-independent-transparency.pdf

Interactive Order-Independent Transparency

Twenty-five years ago, Crow published the shadow volume approach for determining shadowed regions in a scene. A decade ago, Heidmann described a hardware-accelerated stencil bufferbased shadow volume algorithm. However, hardware-accelerated stenciled shadow volume techniques have not been widely adopted by 3D games and applications due in large part to the lack of robustness of described techniques. This situation persists despite widely available hardware support. Specifically what has been lacking is a technique that robustly handles various "hard" situations created by near or far plane clipping of shadow volumes. We describe a robust, artifact-free technique for hardwareaccelerated rendering of stenciled shadow volumes. Assuming existing hardware, we resolve the issues otherwise caused by shadow volume near and far plane clipping through a combination of (1) placing the conventional far clip plane “at infinity”, (2) rasterization with infinite shadow volume polygons via homogeneous coordinates, and (3) adopting a zfail stencil-testing scheme. Depth clamping, a new rasterization feature provided by NVIDIA's GeForce3 & GeForce4 Ti GPUs, preserves existing depth precision by not requiring the far plane to be placed at infinity. We also propose two-sided stencil testing to improve the efficiency of rendering stenciled shadow volumes.

/pdf/practical-and-robust-stenciled-shadow-volumes-for-hardware-32nfis1kko.pdf

Practical and Robust Stenciled Shadow Volumes for Hardware-Accelerated Rendering

A system, method and computer program product are provided for transparency rendering in a graphics pipeline. Initially, colored-transparency information is collected from a plurality of depth layers (i.e. colored-transparency layers, etc.) in a scene to be rendered. The collected colored-transparency information is then stored in memory. The colored-transparency information from the depth layers may then be blended in a predetermined order.

Order-independent transparency rendering system and method

Lights can be conservatively bounded within a depth range. When image pixels are outside of a light's depth range, an associated volume fragment does not have to be rendered. Depth bounds registers can be used to store minimum and maximum depth values for a light. As graphics hardware processes volume fragments overlapping the image, the image's depth values are compared with the values in the depth bounds register. If the image's depth is outside of the depth range for the light, stencil buffer and illumination operations for this volume fragment are bypassed. This optimization can be performed on a per-pixel basis, or simultaneously on a group of adjacent pixels. The depth bounds are calculated from the light, or from the intersection of the volume with one or more other features. A rendering application uses API functions to set the depth bounds for each light and to activate depth bounds checking.

Depth bounds testing

A system and method are provided for using information from at least one depth layer and for collecting information about at least one additional depth layer utilizing a graphics pipeline. Initially, constraining depth layers are provided which, in turn, define a plurality of depth constraints. Next, a plurality of tests is performed involving the constraining depth layers for collecting information about at least one additional depth layer. The information relating to the at least one depth layer may then be used to improve processing in the graphics pipeline. By the foregoing multiple tests, information relating to a plurality of depth layers may be collected during each of a plurality of rendering passes. Initially, information relating to the constraining depth layers and associated depth constraints is provided in the aforementioned manner. Thereafter, information relating to at least one additional depth layer is collected during additional rendering passes using multiple tests on each rendering pass. Once collected, such information relating to the constraining depth layers and the information relating to the at least one additional depth layer may be used to further improve processing in the graphics pipeline.

Cass W. Everitt

Papers

Interactive Order-Independent Transparency

Practical and Robust Stenciled Shadow Volumes for Hardware-Accelerated Rendering

Order-independent transparency rendering system and method

Depth bounds testing

System and method for using and collecting information from a plurality of depth layers