Coherent multiresolution isosurface ray tracing

We implement and evaluate a fast ray tracing method for rendering large structured volumes. Input data is losslessly compressed into an octree, enabling residency in CPU main memory. We cast packets of coherent rays through a min/max acceleration structure within the octree, employing a slice-based technique to amortize the higher cost of compressed data access. By employing a multiresolution level of detail (LOD) scheme in conjunction with packets, coherent ray tracing can efficiently render inherently incoherent scenes of complex data. We achieve higher performance with lesser footprint than previous isosurface ray tracers, and deliver large frame buffers, smooth gradient normals and shadows at relatively lesser cost. In this context, we weigh the strengths of coherent ray tracing against those of the conventional single-ray approach, and present a system that visualizes large volumes at full data resolution on commodity computers.     

Direct Ray Tracing of Phong Tessellation

There are two major ways of calculating ray and parametric surface intersections in rendering. The first is through the use of tessellated triangles, and the second is to use parametric surfaces together with numerical methods such as Newton's method. Both methods are computationally expensive and complicated to implement. In this paper, we focus on Phong Tessellation and introduce a simple direct ray tracing method for Phong Tessellation. Our method enables rendering smooth surfaces in a computationally inexpensive yet robust way.     

Highly Parallel Fast KD-tree Construction for Interactive Ray Tracing of Dynamic Scenes

We present a highly parallel, linearly scalable technique of kd-tree construction for ray tracing of dynamic geometry. We use conventional kd-tree compatible with the high performing algorithms such as MLRTA or frustum tracing. Proposed technique offers exceptional construction speed maintaining reasonable kd-tree quality for rendering stage. The algorithm builds a kd-tree from scratch each frame, thus prior knowledge of motion /deformation or motion constraints are not required. We achieve nearly real-time performance of 7-12 FPS for models with 200K of dynamic triangles at 1024x1024 resolution with shadows and textures.     

Shadows on bump-mapped surfaces in ray tracing

This paper presents a method of generating shadows on bump-mapped surfaces in ray tracing. The method yields images with realistic shadows influenced by bumpy surface geometry. In our method, intersections are calculated between eye/reflection/refraction rays and smooth original surfaces as usual, and the surfaces and shaded according to Blinn's bump mapping. For shadowing, however, we shift the intersection points based on the approximated bumpy surface shape, and the shadow rays are fired from the shifted intersection points. Since the method involves no explicit intersection calculation between rays and bumpy surfaces, it requires only a small amount of computation in addition to conventional ray tracting. It is easy to insert the method into existing ray tracers, and it can be applied to variants of ray tracing algorithms that use shadow rays.     

Shallow Bounding Volume Hierarchies for Fast SIMD Ray Tracing of Incoherent Rays

Photorealistic image synthesis is a computationally demanding task that relies on ray tracing for the evaluation of integrals. Rendering time is dominated by tracing long paths that are very incoherent by construction. We therefore investigate the use of SIMD instructions to accelerate incoherent rays. SIMD is used in the hierarchy construction, the tree traversal and the leaf intersection. This is achieved by increasing the arity of acceleration structures, which also reduces memory requirements. We show that the resulting hierarchies can be built quickly and are smaller than acceleration structures known so far while at the same time outperforming them for incoherent rays. Our new acceleration structure speeds up ray tracing by a factor of 1.6 to 2.0 compared to a highly optimized bounding interval hierarchy implementation, and 1.3 to 1.6 compared to an efficient kd‐tree. At the same time, the memory requirements are reduced by 10–50%. Additionally we show how a caching mechanism in conjunction with this memory efficient hierarchy can be used to speed up shadow rays in a global illumination algorithm without increasing the memory footprint. This optimization decreased the number of traversal steps up to 50%.     

Sorted Deferred Shading for Production Path Tracing

Ray‐traced global illumination (GI) is becoming widespread in production rendering but incoherent secondary ray traversal limits practical rendering to scenes that fit in memory. Incoherent shading also leads to intractable performance with production‐scale textures forcing renderers to resort to caching of irradiance, radiosity, and other values to amortize expensive shading. Unfortunately, such caching strategies complicate artist workflow, are difficult to parallelize effectively, and contend for precious memory. Worse, these caches involve approximations that compromise quality. In this paper, we introduce a novel path‐tracing framework that avoids these tradeoffs. We sort large, potentially out‐of‐core ray batches to ensure coherence of ray traversal. We then defer shading of ray hits until we have sorted them, achieving perfectly coherent shading and avoiding the need for shading caches.     

使用多重纹理实时绘制Phong高光表面

物体表面的高光现象均由镜面反射的一个复杂的非线性表达式描述,这为实时绘制带来了困难,由此本文提出了一种使用纹理映射技术绘制高光表面的方法。首先将具有镜面反射表达式的Phong模型分解成多个预计算的函数,然后存储为纹理图,最后使用多重纹理技术将这些纹理组合起来,实现高光表面的绘制。实验结果表明,本文算法大大提高了绘制的性能。     

Interactive Glossy Reflections using GPU‐based Ray Tracing with Adaptive LOD

We present an interactive GPU‐based algorithm for accurately rendering high‐quality, dynamic glossy reflection effects from both HDR environment maps and local scene objects. Our method uses hardware rasterization to produce primary pixels, and GPU‐based BRDF importance sampling [ [CK07] ] to quickly generate reflected rays. We utilize a fast GPU ray tracer proposed by Carr et al. [ [CHCH06] ] to compute reflection hits. Our main contribution is an adaptive level‐of‐detail (LOD) control algorithm that greatly improves ray tracing performance during reflection shading. Specifically, we use the solid angle represented by each reflected ray to adaptively pick the level of termination in the BVH traversal step during ray tracing. This leads to 2 ～ 3x speedup over an unmodified implementation of [ [CHCH06] ]. Based on the same solid angle measure, we derive a texture filtering formula to reduce reflection aliasing artifacts, taking advantage of hardware MIP mapping. This extends the filtering algorithm presented in [ [CK07] ] from environment mapping to local scene reflection. Using our algorithm, we demonstrate interactive rendering rates for several scenes featuring dynamic lighting and material changes, spatially varying BRDF parameters, and rigid‐body object movement.     

Geometry Textures and Applications†

Geometry textures are a novel geometric representation for surfaces based on height maps. The visualization is done through a graphics processing unit (GPU) ray casting algorithm applied to the whole object. At rendering time, the fine‐scale details (mesostructures) are reconstructed preserving original quality. Visualizing surfaces with geometry textures allows a natural level‐of‐detail (LOD) behaviour. There are numerous applications that can benefit from the use of geometry textures. In this paper, besides a mesostructure visualization survey, we present geometry textures with three possible applications: rendering of solid models, geological surfaces visualization and surface smoothing.     

A Viewpoint-Dependent Approach to Ray Trace Free-Form Surfaces

For convincing realistic scenes objects with free‐form surfaces are essential. Especially for photorealistic rendering pure polygonal models are often not sufficient. We present a new kind of algorithm to render free‐form surfaces in a rendering system based on ray tracing. We describe a triangular patch as usual by its three points and normal vectors, but base the intersection calculation as well on the viewpoint of the camera (or, in general, on the ray itself). Hence, the shape of the object depends to some extent on the sampling rays. However, the resulting differences of, for instance, the shape of the silhouette to the shape of the corresponding shadow is usually not perceived by the observer of the rendered image. Because we perform a direct computation without a tessellation process, the resulting surface, its shadows, and its reflections appear smooth independent of the distance to the camera. Furthermore, the memory consumption depends only linearly on the number of input triangles. Special features like creases, T‐vertices, and darts are also well supported. The computed uv‐coordinates provide a direct means for texture mapping whose visual appearance improves significantly compared to triangle meshes of the same resolution.     

Perturbation methods for interactive specular reflections

We describe an approach for interactively approximating specular reflections in arbitrary curved surfaces. The technique is applicable to any smooth implicitly defined reflecting surface that is equipped with a ray intersection procedure; it is also extremely efficient as it employs local perturbations to interpolate point samples analytically. After ray tracing a sparse set of reflection paths with respect to a given vantage point and static reflecting surfaces, the algorithm rapidly approximates reflections of arbitrary points in 3-space by expressing them as perturbations of nearby points with known reflections. The reflection of each new point is approximated to second-order accuracy by applying a closed-form perturbation formula to one or more nearby reflection paths. This formula is derived from the Taylor expansion of a reflection path and is based on first and second-order path derivatives. After preprocessing, the approach is fast enough to compute reflections of tessellated diffuse objects in arbitrary curved surfaces at interactive rates using standard graphics hardware. The resulting images are nearly indistinguishable from ray traced images that take several orders of magnitude longer to generate     

On-the-fly texture computation for real-time surface shading

Standard texture mapping hardware enables rapid rendering of color mapped surfaces with interpolated surface shading. New algorithms extend this to bump mapping, Phong shading, and reflection mapping. We first introduce the bidirectional reflectance function we wish to optimize, split into diffuse, specular and environment terms. Casting the diffuse term as a table lookup, we introduce lighting tables and efficient ways to compute them for distant lights. We also revisit the geometry of bump mapping, extending Blinn's (1978) results. We consider caching intermediate results for rendering animated rigid bodies, generalizing this to animated surfaces using a technique called parametric rasterization. Finally, we describe efficient reflection mapping and discuss implications for bump-mapped surfaces. We present a fast method for rendering Phong highlights and discuss a special case of a planar surface with simulated water ripples     

Adaptive records for volume irradiance caching

In this paper, we present a new irradiance caching scheme using Monte Carlo ray tracing for efficiently rendering participating media. The irradiance cache algorithm is extended to participating media. Our method allows to adjust the density of cached records depending on illumination changes. Direct and indirect contributions can be stored in the records but also multiple scattering. An adaptive shape of the influence zone of records, depending on geometrical features and irradiance variations, is introduced. To avoid a high density of cached records in low interest areas, a new method controls the density of the cache when adding new records. This record density control depends on the interpolation quality and on the photometric characteristics of the medium. Reducing the number of records accelerates both the computation pass and the rendering pass by decreasing the number of queries to the cache data structure (Kd-tree). Finally, instead of using an expensive ray marching to find records that cover the ray, we gather all the contributive records along the ray. With our method, pre-computing and rendering passes are significantly speeded-up.     

Perception-motivated multiresolution rendering on sole-cube maps

This paper presents a novel GPU-based multiresolution rendering on sole-cube maps (SCMs), which is a variant of geometry images built upon spherical parameterization. Given spherical parametrization of a manifold mesh, the sphere domain is gnomonically projected to a closed cube, which constitutes the 6-chart sole-cube maps. A quadtree structure of SCMs and normal map atlas are then constructed by using the regular re-sampling. Then, by packing the quadtree nodes into the SCMs texture atlas, a new parallel multiresolution rendering is processed on the latest GPU in two rendering passes: the multiresolution node selection in fragment shader; the triangulation in vertex shader followed by the node culling operation in geometry shader. The proposed approach generates adaptive mesh surfaces dynamically, and can be fully implemented in GPU parallelization. The proposed scheme alleviates the computing load of multiresolution mesh refinement on CPU, and our GPU-based multiresolution rendering is demonstrated with a variety of examples. Our user study confirmed that the visual quality of the SCMs multiresolution rendering, in comparison with the meshes/geometry images rendering, is also highly efficient especially for complex models in large-scale virtual environment.     

Priority-driven Ray Tracing

A typical ray tracing algorithm traces a ray through each screen-pixel and spawns secondary rays at ray–object intersection points. Unlike traditional ray tracers which follow these rays recursively, we assign a priority value to each newly spawned ray and insert it into a priority queue. The priority assigned to each ray can be based on a variety of criteria, some of which we explore here. The next ray we trace is always the one with the highest priority in the queue. Occasionally, we trigger display updates when a checkpoint or predefined threshold is reached, providing intermediate images for review and evaluation. Classical ray tracers, once given the rendering specifications, are not controllable by the user. The priority-driven ray tracing, on the other hand, provides the user with a mechanism to steer the rendering and deliver intermediate images amid processing. This paper describes the illumination model of the non-recursive priority-driven ray tracer and evaluates its memory and time requirements. We show that although worst-case memory requirements can be overwhelming, in practice, our method is both useful and feasible. © 1997 by John Wiley & Sons, Ltd.     

基于硬件的实时地平映射

地平映射是用于计算凹凸映射表面阴影的一项技术.在可编程图形硬件上运用并扩展地平映射技术,力求更准确地表达凹凸表面的层次细节.采取在表面切空间对光照向量进行插值的方法,在多遍渲染算法的基础上,使用三维体纹理代替二维地平贴图,一遍渲染即得到较好的实时自阴影效果.     

Ray Specialized Contraction on Bounding Volume Hierarchies

In this paper we propose a simple but effective method to modify a BVH based on ray distribution for improved ray tracing performance. Our method starts with an initial BVH generated by any state‐of‐the‐art offline algorithm. Then by traversing a small set of sample rays we collect statistics at each node of the BVH. Finally, a simple but ultra‐fast BVH contraction algorithm modifies the initial binary BVH to a multi‐way BVH. The overall acceleration for ray‐primitive testing is about 25% for incoherent diffuse rays and 30% for shadow rays, which is significant as a data structure optimization. Similar results are also presented for packet ray tracing, and for Quad‐BVHs the improvement is 10% to 15%. The approach has the advantages of being simple, and compatible with almost any existing BVH and ray tracing techniques, and it require very little extra work to generate the modified tree.     

Ray Accelerator: Efficient and Flexible Ray Tracing on a Heterogeneous Architecture

We present a hybrid ray tracing system, where the work is divided between the CPU cores and the GPU in an integrated chip, and communication occurs via shared memory. Rays are organized in large packets that can be distributed among the two units as needed. Testing visibility between rays and the scene is mostly performed using an optimized kernel on the GPU, but the CPU can help as necessary. The CPU cores typically handle most or all shading, which makes it easy to support complex appearances. For efficiency, the CPU cores shade whole batches of rays by sorting them on material and shading each material using a vectorized kernel. In addition, we introduce a method to support light paths with arbitrary recursion, such as multiple recursive Whitted‐style ray tracing and adaptive sampling where the result of a ray is examined before sending the next, while still batching up rays for the benefit of GPU‐accelerated traversal and vectorized shading. This allows our system to achieve high rendering performance while maintaining the flexibility to accommodate different rendering algorithms.