TBA

We present a novel method for increasing the efficiency of stochastic rasterization of motion and defocus blur. Contrary to earlier approaches, our method is efficient even with the low sampling densities commonly encountered in realtime rendering, while allowing the use of arbitrary sampling patterns for maximal image quality. Our clipless dual-space formulation avoids problems with triangles that cross the camera plane during the shutter interval. The method is also simple to plug into existing rendering systems.

Traditionally, effects that require evaluating multidimensional integrals for each pixel, such as motion blur, depth of field, and soft shadows, suffer from noise due to the variance of the highdimensional integrand. In this paper, we describe a general reconstruction technique that exploits the anisotropy in the temporal light field and permits efficient reuse of samples between pixels, multiplying the effective sampling rate by a large factor. We show that our technique can be applied in situations that are challenging or impossible for previous anisotropic reconstruction methods, and that it can yield good results with very sparse inputs. We demonstrate our method for simultaneous motion blur, depth of field, and soft shadows.

Stochastic renderers produce unbiased but noisy images of scenes that include the advanced camera effects of motion and defocus blur and possibly other effects such as transparency. We present a simple algorithm that selectively adds bias in the form of image space blur to pixels that are unlikely to have high frequency content in the final image. For each pixel, we sweep once through a fixed neighborhood of samples in front to back order, using a simple accumulation scheme. We achieve good quality images with only 16 samples per pixel, making the algorithm potentially practical for interactive stochastic rendering in the near future.

This paper proposes a massively parallel hardware architecture for efficient tracing of incoherent rays, e.g. for global illumination. The general approach is centered around hierarchical treelet subdivision of the acceleration structure and repeated queueing/postponing of rays to reduce cache pressure. We describe a heuristic algorithm for determining the treelet subdivision, and show that our architecture can reduce the total memory bandwidth requirements by up to 90% in difficult scenes. Furthermore the architecture allows submitting rays in an arbitrary order with practically no performance penalty. We also conclude that scheduling algorithms can have an important effect on results, and that using fixed-size queues is not an appealing design choice. Increased auxiliary traffic, including traversal stacks, is identified as the foremost remaining challenge of this architecture.

We describe the architecture of a novel system for precomputing sparse directional occlusion caches. These caches are used for accelerating a fast cinematic lighting pipeline that works in the spherical harmonics domain. The system was used as a primary lighting technology in the movie Avatar, and is able to efficiently handle massive scenes of unprecedented complexity through the use of a flexible, stream-based geometry processing architecture, a novel out-of-core algorithm for creating efficient ray tracing acceleration structures, and a novel out-of-core GPU ray tracing algorithm for the computation of directional occlusion and spherical integrals at arbitrary points.

We discuss the mapping of elementary ray tracing operations---acceleration structure traversal and primitive intersection---onto wide SIMD/SIMT machines. Our focus is on NVIDIA GPUs, but some of the observations should be valid for other wide machines as well. While several fast GPU tracing methods have been published, very little is actually understood about their performance. Nobody knows whether the methods are anywhere near the theoretically obtainable limits, and if not, what might be causing the discrepancy. We study this question by comparing the measurements against a simulator that tells the upper bound of performance for a given kernel. We observe that previously known methods are a factor of 1.5--2.5X off from theoretical optimum, and most of the gap is not explained by memory bandwidth, but rather by previously unidentified inefficiencies in hardware work distribution. We then propose a simple solution that significantly narrows the gap between simulation and measurement. This results in the fastest GPU ray tracer to date. We provide results for primary, ambient occlusion and diffuse interreflection rays.

We introduce a meshless hierarchical representation for solving light transport problems. Precomputed radiance transfer (PRT) and ?nite elements require a discrete representation of illumination over the scene. Non-hierarchical approaches such as per-vertex values are simple to implement, but lead to long precomputation. Hier- archical bases like wavelets lead to dramatic acceleration, but in their basic form they work well only on §at or smooth surfaces. We introduce a hierarchical function basis induced by scattered data approximation. It is decoupled from the geometric representation, allowing the hierarchical representation of illumination on complex objects. We present simple data structures and algorithms for con- structing and evaluating the basis functions. Due to its hierarchical nature, our representation adapts to the complexity of the illumi- nation, and can be queried at different scales. We demonstrate the power of the new basis in a novel precomputed direct-to-indirect light transport algorithm that greatly increases the complexity of scenes that can be handled by PRT approaches.

We present a method for rendering single-bounce indirect illumination in real time on currently available graphics hardware. The method is based on the instant radiosity algorithm, where virtual point lights (VPLs) are generated by casting rays from the primary light source. Hardware shadow maps are then employed for determining the indirect illumination from the VPLs. Our main contribution is an algorithm for reusing the VPLs and incrementally maintaining their good distribution. As a result, only a few shadow maps need to be rendered per frame as long as the motion of the primary light source is reasonably smooth. This yields real-time frame rates even when hundreds of VPLs are used.

We present a novel architecture for hardware-accelerated rendering of point primitives. Our pipeline implements a refined version of EWA splatting, a high quality method for antialiased rendering of point sampled representations. A central feature of our design is the seamless integration of the architecture into conventional, OpenGL-like graphics pipelines so as to complement triangle-based rendering. The specific properties of the EWA algorithm required a variety of novel design concepts including a ternary depth test and using an on-chip pipelined heap data structure for making the memory accesses of splat primitives more coherent. In addition, we developed a computationally stable evaluation scheme for perspectively corrected splats. We implemented our architecture both on reconfigurable FPGA boards and as an ASIC prototype, and we integrated it into an OpenGL-like software implementation. Our evaluation comprises a detailed performance analysis using scenes of varying complexity.

We present a novel technique for approximating ambient occlusion of animated objects. Our method automatically determines the correspondence between animation parameters and per-vertex ambient occlusion using a set of reference poses as its input. Then, at runtime, the ambient occlusion is approximated by taking a dot product between the current animation parameters and static per-vertex coefficients. According to our results, both the computational and storage requirements are low enough for the technique to be directly applicable to computer games running on current graphics hardware. The resulting images are also significantly more realistic than the commonly used static ambient occlusion solutions.

Displaying a synthetic image on a computer display requires determining the colors of individual pixels. To avoid aliasing, multiple samples of the image can be taken per pixel, after which the color of a pixel may be computed as a weighted sum of the samples. The positions and weights of the samples play a major role in the resulting image quality, especially in real-time applications where usually only a handful of samples can be afforded per pixel. This paper presents a new error metric and an optimization method for antialiasing patterns used in image reconstruction. The metric is based on comparing the pattern against a given reference reconstruction filter in spatial domain and it takes into account psychovisually measured angle-specific acuities for sharp features.

We identify and analyze several performance problems in a state-of-the-art physically-based soft shadow volume algorithm, and present an improved method that alleviates these problems by replacing an overly conservative spatial acceleration structure by a more efficient one. The new technique consistently outperforms both the previous method and a ray tracing-based reference solution in several realistic situations while retaining the correctness of the solution and other desirable characteristics of the previous method. These include the unintrusiveness of the original algorithm, meaning that our method can be used as a black-box shadow solver in any offline renderer without requiring multiple passes over the image or other special accommodation. We achieve speedup factors from 1.6 to 12.3 when compared to the previous method.

We present a new, fast algorithm for rendering physically-based soft shadows in ray tracing-based renderers. Our method replaces the hundreds of shadow rays commonly used in stochastic ray tracers with a single shadow ray and a local reconstruction of the visibility function. Compared to tracing the shadow rays, our algorithm produces exactly the same image while executing one to two orders of magnitude faster in the test scenes used. Our first contribution is a two-stage method for quickly determining the silhouette edges that overlap an area light source, as seen from the point to be shaded. Secondly, we show that these partial silhouettes of occluders, along with a single shadow ray, are sufficient for reconstructing the visibility function between the point and the light source.

We present a novel algorithm for rendering physically-based soft shadows in complex scenes. Instead of casting shadow rays, we place both the points to be shaded and the samples of an area light source into separate hierarchies, and compute hierarchically the shadows caused by each occluding triangle. This yields an efficient algorithm with memory requirements independent of the complexity of the scene.

Several algorithms that use graphics hardware to accelerate processing require conservative rasterization in order to function correctly. Conservative rasterization stands for either overestimating or underestimating the size of the triangles. Overestimation is carried out by including all pixels that are at least partially overlapped by the triangle, whereas underestimation includes only the pixels that are fully inside the triangle. None or few algorithms for conservative rasterization have been described in the literature, and current hardware does not explicitly support it. Therefore, we present a simple algorithm, which requires only a small modification to the triangle setup when edge functions are used. Furthermore, the same algorithm can be used for tiled rasterization, where all pixels in a tile (e.g. 8x8 pixels) are visited before moving to the next tile.

The shadow volume algorithm is a popular technique for real-time shadow generation using graphics hardware. Its major disadvantage is that it is inherently fillrate-limited, as the performance is inversely proportional to the area of the projected shadow volumes. We present a new algorithm that reduces the shadow volume rasterization work significantly. With our algorithm, the amount of per-pixel processing becomes proportional to the screenspace length of the visible shadow boundary instead of the projected area. The first stage of the algorithm finds 8x8 pixel tiles, whose 3D bounding boxes are either completely inside or outside the shadow volume.

After that, the second stage performs per-pixel computations only for the potential shadow boundary tiles. We outline a two-pass implementation, and also describe an efficient single-pass hardware architecture, in which the two stages are separated using a delay stream. The only modification required in applications is a new pair of calls for marking the beginning and end of a shadow volume. In our test scenes, the algorithm processes up to 11.5 times fewer pixels compared to current state-of-the-art methods, while reducing the external video memory bandwidth by a factor of up to 17.1.

In this paper we abandon the regular structure of shadow maps. Instead, we transform the visible pixels P(x,y,z) from screen space to the image plane of a light source P'(x',y',z'). The (x',y') are then used as sampling points when the geometry is rasterized into the shadow map. This eliminates the resolution issues that have plagued shadow maps for decades, e.g., jagged shadow boundaries. Incorrect self-shadowing is also greatly reduced, and semi-transparent shadow casters and receivers can be supported. A hierarchical software implementation is outlined.

We present a method for interactive rendering of dynamic models with self-shadows due to time-varying, low-frequency lighting environments. In contrast to previous techniques, the method is not limited to static or pre-animated models. Our main contribution is a hemispherical rasterizer, which rapidly computes visibility by rendering blocker geometry into a 2D occlusion mask with correct occluder fusion. The response of an object to the lighting is found by integrating the visibility function at each of the vertices against the spherical harmonic functions and the BRDF. This yields transfer coefficients that are then multiplied by the lighting coefficients to obtain the final, shadowed exitant radiance. No precomputation is necessary and memory requirements are modest. The method supports both diffuse and glossy BRDFs.

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Shadow maps and shadow volumes are common techniques for computing real-time shadows. We optimize the performance of a hardware-accelerated shadow mapping algorithm by rasterizing the light frustum into the stencil buffer, in a manner similar to the shadow volume algorithm. The pixel shader code that performs shadow tests and illumination computations is applied only to the pixels that are inside the light frustum. We also use deferred shading to further limit the operations to visible pixels. Our technique can be easily plugged into existing applications, and is especially useful for dynamic scenes that contain several local light sources. In our test scenarios, the overall frame rate was up 2.2 times higher than for our comparison methods.

In causal processes decisions do not depend on future data. Many well-known problems, such as occlusion culling, order-independent transparency and edge antialiasing cannot be properly solved using the traditional causal rendering architectures, because future data may change the interpretation of current events.

We propose adding a delay stream between the vertex and pixel processing units. While a triangle resides in the delay stream, subsequent triangles generate occlusion information. As a result, the triangle may be culled by primitives that were submitted after it. We show two- to fourfold efficiency improvements in pixel processing and video memory bandwidth usage in common benchmark scenes. We also demonstrate how the memory requirements of order-independent transparency can be substantially reduced by using delay streams. Finally, we describe how discontinuity edges can be detected in hardware. Previously used heuristics for collapsing samples in adaptive supersampling are thus replaced by connectivity information.