André Maximo

GPU-efficient recursive filtering and summed-area tables

Image processing operations like blurring, inverse convolution, and summed-area tables are often computed efficiently as a sequence of 1D recursive filters. While much research has explored parallel recursive filtering, prior techniques do not optimize across the entire filter sequence. Typically, a separate filter (or often a causal-anticausal filter pair) is required in each dimension. Computing these filter passes independently results in significant traffic to global memory, creating a bottleneck in GPU systems. We present a new algorithmic framework for parallel evaluation. It partitions the image into 2D blocks, with a small band of additional data buffered along each block perimeter. We show that these perimeter bands are sufficient to accumulate the effects of the successive filters. A remarkable result is that the image data is read only twice and written just once, independent of image size, and thus total memory bandwidth is reduced even compared to the traditional serial algorithm. We demonstrate significant speedups in GPU computation.

Introduction to GPU Programming with GLSL

One of the challenging advents in Computer Science in recent years was the fast evolution of parallel processors, specially the GPU – graphics processing unit. GPUs today play a major role in many computational environments, most notably those regarding real-time graphics applications, such as games. The digital game industry is one of the main driving forces behind GPUs, it persistently elevates the state-of-art in Computer Graphics, pushing outstanding realistic scenes to interactive levels. The evolution of photo realistic scenes consequently demands better graphics cards from the hardware industry. Over the last decade, the hardware has not only become a hundred times more powerful, but has also become increasingly customizable allowing programmers to alter some of previously fixed functionalities. This tutorial is an introduction to GPU programming using the OpenGL Shading Language – GLSL. It comprises an overview of graphics concepts and a walk-through the graphics card rendering pipeline. A thorough understanding of the graphics pipeline is extremely important when designing a program in GPU, known as a shader. Throughout this tutorial, the exposition of the GLSL language and GPU programming details are followed closely by examples ranging from very simple to more practical applications. It is aimed at an audience with no or little knowledge on the subject.

Hardware-assisted projected tetrahedra

We present a flexible and highly efficient hardware‐assisted volume renderer grounded on the original Projected Tetrahedra (PT) algorithm. Unlike recent similar approaches, our method is exclusively based on the rasterization of simple geometric primitives and takes full advantage of graphics hardware. Both vertex and geometry shaders are used to compute the tetrahedral projection, while the volume ray integral is evaluated in a fragment shader; hence, volume rendering is performed entirely on the GPU within a single pass through the pipeline. We apply a CUDA‐based visibility ordering achieving rendering and sorting performance of over 6 M Tet/s for unstructured datasets. Furthermore, as each tetrahedron is processed independently, we employ a data‐parallel solution which is neither bound by GPU memory size nor does it rely on auxiliary volume information. In addition, iso‐surfaces can be readily extracted during the rendering process, and time‐varying data are handled without extra burden.

Volume and Isosurface Rendering with GPU-Accelerated Cell Projection*

We present an efficient Graphics Processing Unit GPU‐based implementation of the Projected Tetrahedra (PT) algorithm. By reducing most of the CPU–GPU data transfer, the algorithm achieves interactive frame rates (up to 2.0 M Tets/s) on current graphics hardware. Since no topology information is stored, it requires substantially less memory than recent interactive ray casting approaches. The method uses a two‐pass GPU approach with two fragment shaders. This work includes extended volume inspection capabilities by supporting interactive transfer function editing and isosurface highlighting using a Phong illumination model.

Real-time terrain modeling using CPU: GPU coupled computation

Motivated by the importance of having real-time feedback in sketch-based modeling tools, we propose a framework for terrain edition capable of generating and displaying complex and high-resolution terrains. Our system is efficient and fast enough to allow the user to see the terrain morphing at the same time the drawing edition occurs. We have two types of editing interactions: the user can draw strokes creating elevations and crevices, and previous strokes can be interactively moved to different regions of the terrain. One interesting feature of our tool is that terrain primitives can be interactively manipulated similarly to primitives in vector-graphics tools. We achieve real-time performance in both modeling and rendering using a hybrid CPU -- GPU coupled solution. We maintain a coarse version of the terrain geometry in the CPU by using a quad tree, while a fine version is produced in the GPU using tessellation shaders.

A robust and rotationally invariant local surface descriptor with applications to non-local mesh processing

In recent years, we have witnessed a striking increase in research concerning how to describe a meshed surface. These descriptors are commonly used to encode mesh properties or guide mesh processing, not to augment existing computations by replication. In this work, we first define a robust surface descriptor based on a local height field representation, and present a transformation via the extraction of Zernike moments. Unlike previous work, our local surface descriptor is innately rotationally invariant. Second, equipped with this novel descriptor, we present SAMPLE - similarity augmented mesh processing using local exemplars - a method which uses feature neighbourhoods to propagate mesh processing done in one part of the mesh, the local exemplar, to many others. Finally, we show that SAMPLE can be used in a number of applications, such as detail transfer and parameterization.

GPU-Based Cell Projection for Interactive Volume Rendering

We present a practical approach for implementing the projected tetrahedra (PT) algorithm for interactive volume rendering of unstructured data using programmable graphics cards. Unlike similar works reported earlier, our method employs two fragment shaders, one for computing the tetrahedra projections and another for rendering the elements. We achieve interactive rates by storing the model in texture memory and avoiding redundant projections of implementations using vertex shaders. Our algorithm is capable of rendering over 2.0 M Tet/s on current graphics hardware, making it competitive with recent ray-casting approaches, while occupying a substantially smaller memory footprint

Irregular Grid Raycasting Implementation on the Cell Broadband Engine

Direct volume rendering has become a popular technique for visualizing volumetric data from sources such as scientific simulations, analytic functions, medical scanners, among others. Volume rendering algorithms, such as raycasting, can produce high-quality images, however, the use of raycasting has been limited due to its high demands on computational power and memory bandwidth. In this paper, we propose a new implementation of the raycasting algorithm that takes advantage of the highly parallel architecture of the Cell Broadband Engine processor, with 9 heterogeneous cores, in order to allow efficient raycasting of irregular datasets. All the computational power of the Cell~BE processor, though, comes at the cost of a different programming model. Applications need to be rewritten, which requires using multithreading and vectorized code. In our approach, we tackle this problem by distributing ray computations using the visible faces, and vectorizing the lighting integral operations inside each core. Our experimental results show that we can obtain good speedups reducing the overall rendering time significantly.

Technical Section: Adaptive multi-chart and multiresolution mesh representation

In this paper, we present an adaptive multi-chart and multiresolution mesh representation suitable for both the CPU and the GPU. We build our representation by simplifying a dense-polygon mesh to a base mesh and storing the original geometry in an atlas structure. For both simplification and resolution control, we extend a hierarchical method based on stellar operators to the GPU context. During simplification, we compute local parametrizations to generate charts and an atlas structure to be used later in multiresolution management. Unlike previous approaches, we employ the simplified mesh as our base domain in a novel atlas descriptor combined with a specialized halfedge data structure, achieving superior geometric accuracy while adding a low additional storage. Finally, we show that our mesh representation can be used to adaptively control the mesh resolution in the CPU and the GPU at the same time in a broad range of applications, from mesh editing to rendering.

collecTable: a natural interface for music collections

Introduction and Related Work Tabletop and tangible interfaces have become common in recent years. Technology trends in this area can be found in commercial products, such as Apples iPhone#8482; and Microsoft Surface#8482;, as well as in research ventures, such as Reactable and Perceptive Pixel initiatives. Nevertheless, natural human computer interfaces (HCI) to support this hardware technology are still non-intuitive.