Interactive isosurface ray tracing of time-varying tetrahedral volumes

Journal ArticleAbstract- We describe a system for interactively rendering isosurfaces of tetrahedral finite-element scalar fields using coherent ray tracing techniques on the CPU. By employing state-of-the art methods in polygonal ray tracing, namely aggressive packet/frustum traversal of a bounding volume hierarchy, we can accomodate large and time-varying unstructured data. In conjunction with this efficiency structure, we introduce a novel technique for intersecting ray packets with tetrahedral primitives. Ray tracing is flexible, allowing for dynamic changes in isovalue and time step, visualization of multiple isosurfaces, shadows, and depth-peeling transparency effects. The resulting system offers the intuitive simplicity of isosurfacing, guaranteed-correct visual results, and ultimately a scalable, dynamic and consistently interactive solution for visualizing unstructured volumes

Ray tracing of dynamic scenes

In the last decade ray tracing performance reached interactive frame rates for nontrivial scenes, which roused the desire to also ray trace dynamic scenes. Changing the geometry of a scene, however, invalidates the precomputed auxiliary data-structures needed to accelerate ray tracing. In this thesis we review and discuss several approaches to deal with the challenge of ray tracing dynamic scenes. In particular we present the motion decomposition approach that avoids the invalidation of acceleration structures due to changing geometry. To this end, the animated scene is analyzed in a preprocessing step to split it into coherently moving parts. Because the relative movement of the primitives within each part is small it can be handled by special, pre-built kd-trees. Motion decomposition enables ray tracing of predefined animations and skinned meshed at interactive frame rates. Our second main contribution is the streamed binning approach. It approximates the evaluation of the cost function that governs the construction of optimized kd-trees and BVHs. As a result, construction speed especially for BVHs can be increased by one order of magnitude while still maintaining their high quality for ray tracing.Im letzten Jahrzehnt wurden interaktive Bildwiederholraten bei dem Raytracen von nicht trivialen Szenen erreicht. Dies hat den Wunsch geweckt, auch sich verändernde Szenen mit Raytracing darstellen zu können. Allerdings werden die vorberechneten Datenstrukturen, welche für die Beschleunigung von Raytracing gebraucht werden, durch Veränderungen an der Geometrie einer Szene unbrauchbar gemacht. In dieser Dissertation untersuchen und diskutieren wir mehrere Lösungsansätze für das Problem der Darstellung von sich verändernden Szenen mittels Raytracings. Insbesondere stellen wir den Motion Decomposition Ansatz vor, welcher die bisher nötige Neuberechnung der Beschleunigungsdatenstrukturen aufgrund von Geometrieänderungen zu einem großen Teil vermeidet. Dazu wird in einem Vorberechnungsschritt die animierte Szene untersucht und diese in sich ähnlich bewegende Teile zerlegt. Da dadurch die relative Bewegung der Primitiven der Teilszenen zueinander sehr klein ist kann sie durch spezielle, vorberechnete kd-Bäume toleriert werden. Motion Decomposition ermöglicht das Raytracen von vordefinierte Animationen und Skinned Meshes mit interaktiven Bildwiederholraten. Unser zweiten Hauptbeitrag ist der Streamed Binning Ansatz. Dabei wird die Kostenfunktion, welche die Konstruktion von für Raytracing optimierten kd-Bäumen und BVHs steuert, näherungsweise ausgewertet, wobei deren Qualität kaum beeinträchtigt wird. Im Ergebnis wird insbesondere die Zeit für den Aufbau von BVHs um eine Größenordnung reduziert

Ray tracing of dynamic scenes

In the last decade ray tracing performance reached interactive frame rates for nontrivial scenes, which roused the desire to also ray trace dynamic scenes. Changing the geometry of a scene, however, invalidates the precomputed auxiliary data-structures needed to accelerate ray tracing. In this thesis we review and discuss several approaches to deal with the challenge of ray tracing dynamic scenes. In particular we present the motion decomposition approach that avoids the invalidation of acceleration structures due to changing geometry. To this end, the animated scene is analyzed in a preprocessing step to split it into coherently moving parts. Because the relative movement of the primitives within each part is small it can be handled by special, pre-built kd-trees. Motion decomposition enables ray tracing of predefined animations and skinned meshed at interactive frame rates. Our second main contribution is the streamed binning approach. It approximates the evaluation of the cost function that governs the construction of optimized kd-trees and BVHs. As a result, construction speed especially for BVHs can be increased by one order of magnitude while still maintaining their high quality for ray tracing.Im letzten Jahrzehnt wurden interaktive Bildwiederholraten bei dem Raytracen von nicht trivialen Szenen erreicht. Dies hat den Wunsch geweckt, auch sich verändernde Szenen mit Raytracing darstellen zu können. Allerdings werden die vorberechneten Datenstrukturen, welche für die Beschleunigung von Raytracing gebraucht werden, durch Veränderungen an der Geometrie einer Szene unbrauchbar gemacht. In dieser Dissertation untersuchen und diskutieren wir mehrere Lösungsansätze für das Problem der Darstellung von sich verändernden Szenen mittels Raytracings. Insbesondere stellen wir den Motion Decomposition Ansatz vor, welcher die bisher nötige Neuberechnung der Beschleunigungsdatenstrukturen aufgrund von Geometrieänderungen zu einem großen Teil vermeidet. Dazu wird in einem Vorberechnungsschritt die animierte Szene untersucht und diese in sich ähnlich bewegende Teile zerlegt. Da dadurch die relative Bewegung der Primitiven der Teilszenen zueinander sehr klein ist kann sie durch spezielle, vorberechnete kd-Bäume toleriert werden. Motion Decomposition ermöglicht das Raytracen von vordefinierte Animationen und Skinned Meshes mit interaktiven Bildwiederholraten. Unser zweiten Hauptbeitrag ist der Streamed Binning Ansatz. Dabei wird die Kostenfunktion, welche die Konstruktion von für Raytracing optimierten kd-Bäumen und BVHs steuert, näherungsweise ausgewertet, wobei deren Qualität kaum beeinträchtigt wird. Im Ergebnis wird insbesondere die Zeit für den Aufbau von BVHs um eine Größenordnung reduziert

Sparse Volumetric Deformation

Volume rendering is becoming increasingly popular as applications require realistic solid shape representations with seamless texture mapping and accurate filtering. However rendering sparse volumetric data is difficult because of the limited memory and processing capabilities of current hardware. To address these limitations, the volumetric information can be stored at progressive resolutions in the hierarchical branches of a tree structure, and sampled according to the region of interest. This means that only a partial region of the full dataset is processed, and therefore massive volumetric scenes can be rendered efficiently. The problem with this approach is that it currently only supports static scenes. This is because it is difficult to accurately deform massive amounts of volume elements and reconstruct the scene hierarchy in real-time. Another problem is that deformation operations distort the shape where more than one volume element tries to occupy the same location, and similarly gaps occur where deformation stretches the elements further than one discrete location. It is also challenging to efficiently support sophisticated deformations at hierarchical resolutions, such as character skinning or physically based animation. These types of deformation are expensive and require a control structure (for example a cage or skeleton) that maps to a set of features to accelerate the deformation process. The problems with this technique are that the varying volume hierarchy reflects different feature sizes, and manipulating the features at the original resolution is too expensive; therefore the control structure must also hierarchically capture features according to the varying volumetric resolution. This thesis investigates the area of deforming and rendering massive amounts of dynamic volumetric content. The proposed approach efficiently deforms hierarchical volume elements without introducing artifacts and supports both ray casting and rasterization renderers. This enables light transport to be modeled both accurately and efficiently with applications in the fields of real-time rendering and computer animation. Sophisticated volumetric deformation, including character animation, is also supported in real-time. This is achieved by automatically generating a control skeleton which is mapped to the varying feature resolution of the volume hierarchy. The output deformations are demonstrated in massive dynamic volumetric scenes

Interactive ray tracing of arbitrary implicits with SIMD interval arithmetic

Journal ArticleWe present a practical and efficient algorithm for interactively ray tracing arbitrary implicit surfaces. We use interval arithmetic (IA) both for robust root computation and guaranteed detection of topological features. In conjunction with ray tracing, this allows for rendering literally any programmable implicit function simply from its definition. Our method requires neither special hardware, nor preprocessing or storage of any data structure. Efficiency is achieved through SIMD optimization of both the interval arithmetic computation and coherent ray traversal algorithm, delivering interactive results even for complex implicit functions

Estimating performance of an ray- tracing ASIC design

Journal ArticleRecursive ray tracing is a powerful rendering technique used to compute realistic images by simulating the global light transport in a scene. Algorithmic improvements and FPGA-based hardware implementations of ray tracing have demonstrated realtime performance but hardware that achieves performance levels comparable to commodity rasterization graphics chips is still not available. This paper describes the architecture and ASIC implementations of the DRPU design (Dynamic Ray Processing Unit) that closes this performance gap. The DRPU supports fully programmable shading and most kinds of dynamic scenes and thus provides similar capabilities as current GPUs. It achieves high efficiency due to SIMD processing of floating point vectors, massive multithreading, synchronous execution of packets of threads, and careful management of caches for scene data. To support dynamic scenes B-KD trees are used as spatial index structures that are processed by a custom traversal and intersection unit and modified by an Update Processor on scene changes

Hardware Accelerators for Animated Ray Tracing

Future graphics processors are likely to incorporate hardware accelerators for real-time ray tracing, in order to render increasingly complex lighting effects in interactive applications. However, ray tracing poses difficulties when drawing scenes with dynamic content, such as animated characters and objects. In dynamic scenes, the spatial datastructures used to accelerate ray tracing are invalidated on each animation frame, and need to be rapidly updated. Tree update is a complex subtask in its own right, and becomes highly expensive in complex scenes. Both ray tracing and tree update are highly memory-intensive tasks, and rendering systems are increasingly bandwidth-limited, so research on accelerator hardware has focused on architectural techniques to optimize away off-chip memory traffic. Dynamic scene support is further complicated by the recent introduction of compressed trees, which use low-precision numbers for storage and computation. Such compression reduces both the arithmetic and memory bandwidth cost of ray tracing, but adds to the complexity of tree update.This thesis proposes methods to cope with dynamic scenes in hardware-accelerated ray tracing, with focus on reducing traffic to external memory. Firstly, a hardware architecture is designed for linear bounding volume hierarchy construction, an algorithm which is a basic building block in most state-of-the-art software tree builders. The algorithm is rearranged into a streaming form which reduces traffic to one-third of software implementations of the same algorithm. Secondly, an algorithm is proposed for compressing bounding volume hierarchies in a streaming manner as they are output from a hardware builder, instead of performing compression as a postprocessing pass. As a result, with the proposed method, compression reduces the overall cost of tree update rather than increasing it. The last main contribution of this thesis is an evaluation of shallow bounding volume hierarchies, common in software ray tracing, for use in hardware pipelines. These are found to be more energy-efficient than binary hierarchies. The results in this thesis both confirm that dynamic scene support may become a bottleneck in real time ray tracing, and add to the state of the art on tree update in terms of energy-efficiency, as well as the complexity of scenes that can be handled in real time on resource-constrained platforms