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Lightmaps that respond to normal mapping are commonly used in video games. This short paper describes a novel parameterization of a standard lightmap encoding, Ambient Highlight Direction (AHD) --- a model for directional irradiance consisting of ambient and directional light --- that eliminates common interpolation artifacts. It also describes a technique for fitting the AHD model to lighting represented as spherical harmonics, where the unknown model parameters are solved in the null space of the constraint that irradiance is preserved.

We present progressive photon beams, a new algorithm for rendering complex lighting in participating media. Our technique is efficient, robust to complex light paths, and handles heterogeneous media and anisotropic scattering while provably converging to the correct solution using a bounded memory footprint. We achieve this by extending the recent photon beams variant of volumetric photon mapping. We show how to formulate a progressive radiance estimate using photon beams, providing the convergence guarantees and bounded memory usage of progressive photon mapping. Progressive photon beams can robustly handle situations that are difficult for most other algorithms, such as scenes containing participating media and specular interfaces, with realistic light sources completely enclosed by refractive and reflective materials. Our technique handles heterogeneous media and also trivially supports stochastic effects such as depth-of-field and glossy materials. Finally, we show how progressive photon beams can be implemented efficiently on the GPU as a splatting operation, making it applicable to interactive and real-time applications. These features make our technique scalable, providing the same physically-based algorithm for interactive feedback and reference-quality, unbiased solutions.

Many rendering algorithms willingly sacrifice accuracy, favoring plausible shading with high-performance. Modular Radiance Transfer (MRT) models coarse-scale, distant indirect lighting effects in scene geometry that scales from high-end GPUs to low-end mobile platforms. MRT eliminates scene-dependent precomputation by storing compact transport on simple shapes, akin to bounce cards used in film production. These shapes' modular transport can be instanced, warped and connected on-the-fly to yield approximate light transport in large scenes. We introduce a prior on incident lighting distributions and perform all computations in low-dimensional subspaces. An implicit lighting environment induced from the low-rank approximations is in turn used to model secondary effects, such as volumetric transport variation, higher-order irradiance, and transport through lightfields. MRT is a new approach to precomputed lighting that uses a novel low-dimensional subspace simulation of light transport to uniquely balance the need for high-performance and portable solutions, low memory usage, and fast authoring iteration.

We investigate the representation of signals defined on triangle meshes using linearly interpolated vertex attributes. Compared to texture mapping, storing data only at vertices yields significantly lower memory overhead and less expensive runtime reconstruction. However, standard approaches to determine vertex values such as point sampling or averaging triangle samples lead to suboptimal approximations. We discuss how an optimal solution can be efficiently calculated using continuous least-squares. In addition, we propose a regularization term that allows us to minimize gradient discontinuities and mach banding artifacts while staying close to the optimum. Our method has been integrated in a game production lighting tool and we present examples of representing signals such as ambient occlusion and precomputed radiance transfer in real game scenes, where vertex baking was used to free up resources for other game components.

Previous methods for soft shadows numerically integrate over many light directions at each receiver point, testing blocker visibility in each direction. We introduce a method for real-time soft shadows in dynamic scenes illuminated by large, low-frequency light sources where such integration is impractical. Our method operates on vectors representing low-frequency visibility of blockers in the spherical harmonic basis. Blocking geometry is modeled as a set of spheres; relatively few spheres capture the low-frequency blocking effect of complicated geometry. At each receiver point, we compute the product of visibility vectors for these blocker spheres as seen from the point. Instead of computing an expensive SH product per blocker as in previous work, we perform inexpensive vector sums to accumulate the log of blocker visibility. SH exponentiation then yields the product visibility vector over all blockers. We show how the SH exponentiation required can be approximated accurately and efficiently for low-order SH, accelerating previous CPU-based methods by a factor of 10 or more, depending on blocker complexity, and allowing real-time GPU implementation.

One of the most common tasks in computer animation is inverse-kinematics, or determining a joint configuration required to place a particular part of an articulated character at a particular location in global space. Inverse-kinematics is required at design-time to assist artists using commercial 3D animation packages, for motion capture analysis, and for run-time applications such as games. We present an efficient inverse-kinematics methodology based on the interpolation of example motions and positions. The technique is demonstrated on a number of inverse-kinematics positioning tasks for a human figure. In addition to simple positioning tasks, the method provides complete motion sequences that satisfy an inverse-kinematic goal. The interpolation at the heart of the algorithm allows an artist's influence to play a major role in ensuring that the system always generates plausible results. Due to the lightweight nature of the algorithm, we can position a character at extremely high frame rates, making the technique useful for time-critical run-time applications such as games.

Presents a brute-force ray-tracing system for interactive volume visualization. The system runs on a conventional (distributed) shared-memory multiprocessor machine. For each pixel, we trace a ray through a volume to compute the color for that pixel. Although this method has a high intrinsic computational cost, its simplicity and scalability make it ideal for large data sets on current high-end parallel systems. To gain efficiency, several optimizations are used, including a volume bricking scheme and a shallow data hierarchy. These optimizations are used in three separate visualization algorithms: isosurfacing of rectilinear data, isosurfacing of unstructured data, and maximum-intensity projection on rectilinear data. The system runs interactively (i.e. at several frames per second) on an SGI Reality Monster. The graphics capabilities of the Reality Monster are used only for display of the final color image.

Traditionally, texture coordinates have been generated based solely on the model’s geometry, often even before a model’s textures have been created. With the arrival of new technologies, such as 3D paint programs, weaknesses of a static optimization pre-process are becoming apparent. These weaknesses arise from constructing a parameterization based solely on the model’s geometry, ignoring the fact that detail is not uniformly spaced throughout the texture space. In fact, certain regions of the texture are more important than other regions. In this paper we introduce the notion of the “importance map” and describe how importance values are derived from both intrinsic properties of the texture and user-guided highlights. Furthermore, we describe how importance maps are used to drive the texture coordinate optimization. Finally, we show how this optimization process can be integrated into a 3D painting environment, enabling periodic optimization at any stage of texture design.

Ambient Occlusion and Ambient Obscurance are coarse approximations to global illumination from ambient lighting, commonly used in film and games. This paper describes a system that computes Ambient Obscurance over the vertices of complex polygon meshes. Novel contributions include pre-processing necessary for "triangle soup" scene representations to minimize artifacts, a compact model for different classes of instanced decorator objects such as trees and shrubs, a compact model for pre-computed visibility to be used on dynamically placed objects, and an approximation to model the occlusion of small decorator objects when ray tracing.

Modular Radiance Transfer (MRT) is a recent technique for computing approximate direct-to-indirect transport. Scenes are dynamically constructed by warping and connecting simple shapes and compact transport operators are only precomputed on these simple shapes. MRT ignores fine-scale transport from "clutter" objects inside the scene, and computes light transport with reduced dimensional operators, which allows extremely high performance but can lead to significant approximation error. We present several techniques to alleviate this limitation, allowing the light transport from clutter in a scene to be accounted for. We derive additional low-rank delta operators to compensate for these missing light transport paths by modeling indirect shadows and interreflections from, and onto, clutter objects in the scene. We retain MRT's scene-independent precomputation and augment its scene-dependent initialization with clutter transport generation, resulting in increased accuracy without a performance penalty. Our implementation is simple, requiring a few small matrix-vector multiplications that generate a delta lightmap added to MRT's output, and does not adversely affect the performance benefits of the overall algorithm.

Real-time rendering of indirect lighting significantly enhances the sense of realism in video games. Unfortunately, previously including such effects often required time consuming scene dependent precomputation and heavy runtime computations unsuitable for low-end devices, such as mobile phones or game consoles. Modular Radiance Transfer (MRT) [Loos et al. 2011] is a recent technique that computes approximate direct-to-indirect transfer [Hasan et al. 2006; Kontkanen et al. 2006; Lehtinen et al. 2008] by warping and combining light transport, in real-time, from a small library of simple shapes. This talk focusses on implementation issues of the MRT technical paper, including how our run time is designed to scale across many different platforms, from iPhones to modern GPUs.

Normal mapping is a common technique used in video games, decoupling surface details stored at high spatial frequencies, which are often tiled or repeated, from lighting information that is both unique and stored at a lower sampling rate. This paper presents two techniques that couple normal maps on static geometry with soft shadows from smooth distant lighting in a more efficient manner compared with previous work. In the first technique, the visibility function is represented using low-order spherical harmonics, and the product of the Lambertian-clamped cosine function and the lighting environment is tabulated in textures. The second technique uses principal component analysis to compress the visibility function, decreasing the data size and increasing the performance. Finally, we also examine the efficiency of four common parameterizations for spherical harmonics.

Many games have used some form of lighting pre-computation to increase realism. As computational power has increased these techniques have evolved from traditional diffuse scalar radiosity, to vector irradiance formulations of radiosity that decouple normal variation to techniques that can model non-diffuse materials. This talk will cover how these techniques have been used in games over time and the outstanding research problems going forward in this area. The challenge of getting your research adopted in games, or doing research that games find interesting and relevant, will also be discussed.

High dynamic range (HDR) images are increasingly employed in games and interactive applications for accurate rendering and illumination. One disadvantage of HDR images is their large data size; unfortunately, even though solutions have been proposed for future hardware, commodity graphics hardware today does not provide any native compression for HDR textures.In this paper, we perform extensive study of possible methods for supporting compressed HDR textures on commodity graphics hardware. A desirable solution must be implementable on DX9 generation hardware, as well as meet the following requirements. First, the data size should be small and the reconstruction quality must be good. Second, the decompression must be efficient; in particular, bilinear/trilinear/anisotropic texture filtering ought to be performed via native texture hardware instead of custom pixel shader filtering.We present a solution that optimally meets these requirements. Our basic idea is to convert a HDR texture to a custom LUVW space followed by an encoding into a pair of 8-bit DXT textures. Since DXT format is supported on modern commodity graphics hardware, our approach has wide applicability. Our compression ratio is 3:1 for FP16 inputs, allowing applications to store 3 times the number of HDR texels in the same memory footprint. Our decompressor is efficient and can be implemented as a short pixel program. We leverage existing texturing hardware for fast decompression and native texture filtering, allowing HDR textures to be utilized just like traditional 8-bit DXT textures. Our reduced data size has a further advantage: it is even faster than rendering from uncompressed HDR textures due to our reduced texture memory access. Given the quality and efficiency, we believe our approach suitable for games and interactive applications.

Normal mapping is a variant of bump mapping that is commonly used in computer games. It models complex surface variations by explicitly storing a surface normal in a texture map. However, it has not been used with precomputed radiance transfer (PRT), a technique for modeling an object's response to a parameterized model of lighting, which enables interactive rendering of complex global illumination effects such as soft shadows and interreflections. This paper presents several techniques that effectively combine normal mapping and precomputed radiance transfer for rigid objects. In particular, it investigates representing the convolved radiance function in various bases and borrowing concepts from the separable decomposition of BRDF's.

Interactive rendering of realistic objects under general lighting models poses three principal challenges. Handling complex light transport phenomena like shadows, inter-reflections, caustics and sub-surface scattering is difficult to do in real time. Integrating these effects over large area light sources compounds the difficulty, and finally real objects have complex spatially-varying BRDF's. Precomputed Radiance Transfer (PRT) encapsulates a family of techniques that partially addresses these challenges. PRT is an active of area of research that has relevance to both the academic research community and practitioners of interactive computer graphics. This technique and its variants are being actively investigated in the game development community and there is quite a lot of interest due to the recent appearance of PRT techniques in games such as "Halo 2".This course covers these techniques, compares them and discusses their various strengths and weaknesses. A more rigorous derivation directly from the rendering equation is presented along with practical implementation details, both of which are generally not included in technical papers. After introducing the necessary foundation (rendering equation, basis functions, etc.), we begin with simple PRT for diffuse objects. We continue with general PRT using the concept of transfer matrices, which allow for arbitrary reflectance models. The possible choices for basis functions are discussed as well. Different light source representations are presented and compared. Finally, we discuss practical issues with PRT, such as data compression, spatial sampling, normal mapping, precomputation, and more. By the end of the course the audience will be able to pick the right algorithm for their needs and will hopefully have gained some of the unpublished insights the speakers have gained by working in this area.

We examine a rendering system that interactively ray traces an image on a conventional multiprocessor. The implementation is "brute force" in that it explicitly traces rays through every screen pixel, yet pays careful attention to system resources for acceleration. The design of the system is described, along with issues related to material models, lighting and shadows, and frameless rendering. The system is demonstrated for several different types of input scenes.

A sequence of images taken along a camera trajectory captures a subset of scene appearance. If visibility space is the space that encapsulates the appearance of the scene at every conceivable pose and viewing angle, then the act of acquiring the image sequence constitutes "carving a volume in visibility space." We call such a volume a visual tunnel. The analysis of the visual tunnel allows us to do the following: predict the range of virtual camera poses in which the images can be reconstructed totally using the captured rays, predict which parts of the image can be generated for a given virtual camera pose, and plan camera paths for scene visualization at desired locations. We describe our visual tunnel concept and provide illustrative examples in 2D and 3D.

We present a new set of non-photorealistic rendering (NPR) tools for processing video. Our approach is to treat the video as a space-time volume of image data. Previous tools to process video for an impressionist effect have painted collections of two-dimensional strokes on each successive frame of video. In contrast, we create a set of "rendering solids." Each rendering solid is a function defined over an interval of time; when evaluated at a particular time within that interval, it provides parameters necessary for rendering an NPR primitive. Rendering solids can be rendered interactively, giving immediate feedback to an artist along with the ability to modify styles in real time.Benefits of our approach include: a more unified treatment of the video volume's spatial and temporal dimensions; interactive, aesthetic flexibility and control; and the extension of stylized rendering techniques for video beyond the impressionist styles previously explored. We show example styles inspired by impressionist, cubist, and abstract art of the past century.

We present a new, real-time method for rendering diffuse and glossy objects in low-frequency lighting environments that captures soft shadows, interreflections, and caustics. As a preprocess, a novel global transport simulator creates functions over the object's surface representing transfer of arbitrary, low-frequency incident lighting into transferred radiance which includes global effects like shadows and interreflections from the object onto itself. At run-time, these transfer functions are applied to actual incident lighting. Dynamic, local lighting is handled by sampling it close to the object every frame; the object can also be rigidly rotated with respect to the lighting and vice versa. Lighting and transfer functions are represented using low-order spherical harmonics. This avoids aliasing and evaluates efficiently on graphics hardware by reducing the shading integral to a dot product of 9 to 25 element vectors for diffuse receivers. Glossy objects are handled using matrices rather than vectors. We further introduce functions for radiance transfer from a dynamic lighting environment through a preprocessed object to neighboring points in space. These allow soft shadows and caustics from rigidly moving objects to be cast onto arbitrary, dynamic receivers. We demonstrate real-time global lighting effects with this approach.

Modern modeling systems enable artists to create highquality content, but provide limited support for interactive applications. Although complex forms can be constructed either by hand or with geometry capture technologies, once they are created, they are difficult to modify, particularly at runtime. Interpolation provides a way to leverage artist-generated source material. We present a methodology for efficient runtime interpolation between multiple forms. Linear plus radial basis functions provide the key mathematical support for the interpolation. Once our system is provided with example forms, it generates a continuous range of forms we call a shape. We also apply the shape interpolation methodology to articulated figures and human face models to create smoothly skinned figures that deform in natural ways. Unlike previous formulations, the one presented here is efficient enough to support interactive design of the abstract interpolation space as well as support runtime interpolation of the forms in interactive applications such as games. The reader is encouraged to visit the project’s website for more information and late-breaking results at http:\\research.microsoft.com\graphics\hfap.

Shadows, which play an important role in perceiving the shape and texture of an object, are simulated interactively in a real time, self-shadowing of a bump mapped surface for a computer rendered object. A computer graphics textured object function defines a horizon map over an orientation in a tangent space of the object using different textures or basis functions. The implementation can be performed using commodity graphics hardware by precomputing the horizon map for limited visibility for each point on the bump mapped surface given light in each of a plurality of radial directions. The horizon map is used to produce self-shadowing of the bump mapped surface of the object.

Presents three techniques for reconstructing lumigraphs/lightfields on commercial ccNUMA parallel distributed shared memory computers. The first method is a parallel extension of the software-based lightfield method proposed by M. Levoy and P. Hanrahan (1996). This expands the ray/two-plane intersection test along the film plane, which effectively becomes scan conversion. The second method extends this idea by using a shear/warp factorization that accelerates rendering. The third technique runs on an SGI Reality Monster using up to eight graphics pipes and texture mapping hardware to reconstruct images. We characterize the memory access patterns exhibited using the hardware-based method and use this information to reconstruct images from a tiled UV plane. We describe a method to use quad-cubic reconstruction kernels. We analyze the memory access patterns that occur when viewing lumigraphs. This allows us to ascertain the cost/benefit ratio of various tilings of the texture plane.

It was illustrated in that the light leaving the con vex hull of an object or entering a convex region of empty space can be fully characterized by a D function over the space of rays crossing a surface surrounding the object or surrounding the empty space Methods to repre sent this function and quickly render individual images from this representation given an arbitrary cameras were also de scribed This paper extends the work outlined by Gortler et al by demonstrating a taxonomy of methods to accelerate the rendering process by trading o quality for time Given the speci c limitation of a given hardware con guration we discuss methods to tailor a critical time rendering strategy using these methods CR Descriptors I Computer Graphics Three Dimensional Graphics and Realism Additional