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Item SPAF: Sub-texel Precision Anisotropic Filtering(The Eurographics Association, 2001) Shin, Hyun-Chul; Lee, Jin-Aeon; Kim, Lee-Sup; Kurt Akeley and Ulrich NeumannTexture mapping is a technique which most effectively improves the realism of computer-generated scenes in 3D Graphics. Trilinear filtering of the mip-mapped textue has been popular as a texture filtering method but it blurs images on the surface of objects angled obliquely away from the viewer in a scene. Various anisotropic filtering methods like footprint assembly, Feline, and fast footprint mip-mapping have been proposed to satisfy the desire for the high quality image [7]. In spite of the increase of the memory bandwidth, tie memory bandwidth limit is still the bottleneck of the texture filtering hardware. Moreover, it is very important to keep the quality of rendered image good. In this paper, we propose Sub-texel Precision Anisonopic Filtering (SPAF) which filters texels in a region that covers a quadrilateral footprint with the weights. The weight plays a key role in effective filtering to render the image of high quality with the restricted number of texels loaded from memory for real-time filtering. First, the area coverage based texel filtering scheme is introduced to obtain the footprint's coverage for each texel on the sub-texel precision leading to the small weight table size. Second, the Gaussian weight is applied to this footprinfs coverage for each texel to reduce the artifacts. Therefore, the quality of rendered images is superior to other anisotropic filtering methods in the same restricted number of texels. And the size ofthis weight table is several hundred KBytes which is much smaller than fast footprint mip-mapping. This small ROM table size enables the SPAF to be implemented at feasible hardware costs.Item Interactive Rendering of Atmospheric Scattering Effects Using Graphics Hardware(The Eurographics Association, 2002) Dobashi, Yoshinori; Yamamoto, Tsuyoshi; Nishita, Tomoyuki; Thomas Ertl and Wolfgang Heidrich and Michael DoggettTo create realistic images using computer graphics, an important element to consider is atmospheric scattering, that is, the phenomenon by which light is scattered by small particles in the air. This effect is the cause of the light beams produced by spotlights, shafts of light, foggy scenes, the bluish appearance of the earth s atmosphere, and so on. This paper proposes a fast method for rendering the atmospheric scattering effects based on actual physical phenomena. In the proposed method, look-up tables are prepared to store the intensities of the scattered light, and these are then used as textures. Realistic images are then created at interactive rates by making use of graphics hardware.Item Quasi-Linear Depth Buffers With Variable Resolution(The Eurographics Association, 2001) Lapidous, Eugene; Jiao, Guofang; Zhang, Jianbo; Wilson, Timothy; Kurt Akeley and Ulrich NeumannIn this paper we present new class of variable-resolution depth buffers, providing a flexible trade-off between depth precision in the distant areas of the view volume and performance. These depth buffers can be implemented using linear or quasi-linear mapping function of the distance to the camera to the depth in the screens pace. In particular, the complementary Z buffer algorithm combines simplicity of implementation with significant bandwidth savings. A variable-resolution depth buffer saves bandwidth by changing size of the per-pixel depth access from 24 bits to 16 bits when distance to the pixel from the camera becomes larger than a given threshold, This distance is selected in order to keep the resulting resolution equal or larger than the resolution of the 24-bit screen Z buffer. For dynamic ratios of the distances between far and near planes 500 and above, bandwidth savings may exceed 20%. Quasi-linear depth floating-point depth buffers are best at high dynamic ratios; 3D hardware should support per-frame setting of the optimal depth buffer type and format. Per-frame adjustment of the resolution switch distance allows balancing performance with depth precision and should be exposed in the graphics A PI.Item Adaptive Texture Maps(The Eurographics Association, 2002) Kraus, Martin; Ertl, Thomas; Thomas Ertl and Wolfgang Heidrich and Michael DoggettWe introduce several new variants of hardware-based adaptive texture maps and present applications in two, three, and four dimensions. In particular, we discuss representations of images and volumes with locally adaptive resolution, lossless compression of light fields, and vector quantization of volume data. All corresponding texture decoders were successfully integrated into the programmable texturing pipeline of commercial off-the-shelf graphics hardware.Item The Ray Engine(The Eurographics Association, 2002) Carr, Nathan A.; Hall, Jesse D.; Hart, John C.; Thomas Ertl and Wolfgang Heidrich and Michael DoggettAssisted by recent advances in programmable graphics hardware, fast rasterization-based techniques have made significant progress in photorealistic rendering, but still only render a subset of the effects possible with ray tracing. We are closing this gap with the implementation of ray-triangle intersection as a pixel shader on existing hardware. This GPU ray-intersection implementation reconfigures the geometry engine into a ray engine that efficiently intersects caches of rays for a wide variety of host-based rendering tasks, including ray tracing, path tracing, form factor computation, photon mapping, subsurface scattering and general visibility processing.Item Low Latency Photon Mapping Using Block Hashing(The Eurographics Association, 2002) Ma, Vincent C. H.; McCool, Michael D.; Thomas Ertl and Wolfgang Heidrich and Michael DoggettFor hardware accelerated rendering, photon mapping is especially useful for simulating caustic lighting effects on non-Lambertian surfaces. However, an efficient hardware algorithm for the computation of the k nearest neighbours to a sample point is required. Existing algorithms are often based on recursive spatial subdivision techniques, such as kd-trees. However, hardware implementation of a tree-based algorithm would have a high latency, or would require a large cache to avoid this latency on average. We present a neighbourhood-preserving hashing algorithm that is low-latency and has sub-linear access time. This algorithm is more amenable to fine-scale parallelism than tree-based recursive spatial subdivision, and maps well onto coherent block-oriented pipelined memory access. These properties make the algorithm suitable for implementation using future programmable fragment shaders with only one stage of dependent texturing.Item Vertex-based Anisotropic Texturing(The Eurographics Association, 2001) Olano, Marc; Mukherjee, Shrijeet; Dorbie, Angus; Kurt Akeley and Ulrich NeumannMIP mapping is a common method used by graphics hardware to avoid texture aliasing. In many situations, MIP mapping over-blurs in one direction to prevent aliasing in another. Anisotropic texturing reduces this blurring by allowing differing degrees of filtering in different directions, but is not as common in hardware due to the implementation complexity of current techniques. We present a new algorithm that enables anisotropic texturing on any current MIP map graphics hardware supporting MIP level biasing, available in OpenGL 7.2 or through the GLEXT-texture-lod-bias or GL-SGIX-texture-lod-bias OpenGL extensions. The new algorithm computes anisotropic filter footprint parameters per vertex. It constructs the anisotropic filter out of several MIP map texturing passes or multitexture lookups. Each lookup uses MIP level bias and perturbed texture coordinates to place one probe used to construct the more complex filter profile.Item Algorithms for Division Free Perspective Correct Rendering(The Eurographics Association, 2000) Barenbrug, B.; Peters, F.J.; Overveld, C.W.A.M. van; I. Buck and G. Humphreys and P. HanrahanWell known implementations for perspective correct rendering of planar polygons require a division per rendered pixel. Such a division is better to be avoided as it is an expensive operation in terms of silicon gates and clock cycles. In this paper we present a family of efficient midpoint algorithms that can be used to avoid division operators. These algorithms do not require more than a small number of additions per pixel. We show how these can be embedded in scan line algorithms and in algorithms that use mipmaps. Experiments with software implementations show that the division free algorithms are a factor of two faster, provided that the polygons are not too small. These algorithms are however most profitable when realised in hardware.Item Perlin Noise Pixel Shaders(The Eurographics Association, 2001) Hart, John C.; Kurt Akeley and Ulrich NeumannWhile working on a method for supporting real-time procedural solid texturing, we developed a general purpose multipass pixel shader to generate the Perlin noise function. We implemented this algorithm on SGI workstations using accelerated OpenGL PixelMap and PixelTransfer operations, achieving a rate of 2.5 Hz for a 256x256 image. We also implemented the noise algorithm on the NVidia GeForce2 using register combiners. Our register combiner implementation required 375 passes, but ran at 1.3 Hz. This exercise illustrated a variety of abilities and shortcomings of current graphics hardware. The paper concludes with an exploration of directions for expanding pixel shading hardware to further support iterative multipass pixel-shader applications.Item GI-Cube: An Architecture for Volumetric Global Illumination and Rendering(The Eurographics Association, 2000) Dachille, Frank; Kaufman, Arie; I. Buck and G. Humphreys and P. HanrahanThe power and utility of volume rendering is increased by global illumination. We present a hardware architecture, GI-Cube, designed to accelerate volume rendering, empower volumetric global illumination, and enable a host of ray-based volumetric processing. The algorithm reorders ray processing based on a partitioning of the volume. A cache enables efficient processing of coherent rays within a hardware pipeline. We study the flexibility and performance of this new architecture using both high and low level simulations.