| 1. |
- Barringer, Rasmus, et al.
(author)
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A(4): Asynchronous Adaptive Anti-Aliasing using Shared Memory
- 2013
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In: ACM Transactions on Graphics. - : Association for Computing Machinery (ACM). - 0730-0301 .- 1557-7368. ; 32:4, s. 100-100
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Journal article (peer-reviewed)abstract
- Edge aliasing continues to be one of the most prominent problems in real-time graphics, e.g., in games. We present a novel algorithm that uses shared memory between the GPU and the CPU so that these two units can work in concert to solve the edge aliasing problem rapidly. Our system renders the scene as usual on the GPU with one sample per pixel. At the same time, our novel edge aliasing algorithm is executed asynchronously on the CPU. First, a sparse set of important pixels is created. This set may include pixels with geometric silhouette edges, discontinuities in the frame buffer, and pixels/polygons under user-guided artistic control. After that, the CPU runs our sparse rasterizer and fragment shader, which is parallel and SIMD:ified, and directly accesses shared resources (e.g., render targets created by the GPU). Our system can render a scene with shadow mapping with adaptive anti-aliasing with 1 6 samples per important pixel faster than the GPU with 8 samples per pixel using multi-sampling anti-aliasing. Since our system consists of an extensive code base, it will be released to the public for exploration and usage.
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| 2. |
- Barringer, Rasmus, et al.
(author)
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Dynamic Ray Stream Traversal
- 2014
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In: ACM Transactions on Graphics. - : Association for Computing Machinery (ACM). - 0730-0301 .- 1557-7368. ; 33:4, s. 9-151
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Conference paper (peer-reviewed)abstract
- While each new generation of processors gets larger caches and more compute power, external memory bandwidth capabilities increase at a much lower pace. Additionally, processors are equipped with wide vector units that require low instruction level divergence to be efficiently utilized. In order to exploit these trends in ray tracing, we present an alternative to traditional depth-first ray traversal that takes advantage of the available cache hierarchy, and provides high SIMD efficiency, while keeping memory bus traffic low. Our main contribution is an efficient algorithm for traversing large packets of rays against a bounding volume hierarchy in a way that groups coherent rays during traversal. In contrast to previous large packet traversal methods, our algorithm allows for individual traversal order for each ray, which is essential for efficient ray tracing. Ray tracing algorithms is a mature research field in computer graphics, and despite this, our new technique increases traversal performance by 36-53%, and is applicable to most ray tracers.
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| 3. |
- Barringer, Rasmus, et al.
(author)
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Dynamic Stackless Binary Tree Traversal
- 2013
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In: Journal of Computer Graphics Techniques. - 2331-7418. ; 2:1, s. 38-49
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Journal article (peer-reviewed)abstract
- A fundamental part of many computer algorithms involves traversing a binary tree. One notable example is traversing a space-partitioning acceleration structure when computing ray-traced images. Traditionally, the traversal requires a stack to be temporarily stored for each ray, which results in both additional storage and memory-bandwidth usage. We present a novel algorithm for traversing a binary tree that does not require a stack and, unlike previous approaches, works with dynamic descent direction without restarting. Our algorithm will visit exactly the same sequence of nodes as a stack-based counterpart with extremely low computational overhead. No additional memory accesses are made for implicit binary trees. For sparse trees, parent links are used to backtrack the shortest path. We evaluate our algorithm using a ray tracer with a bounding volume hierarchy for which source code is supplied.
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| 4. |
- Barringer, Rasmus
(author)
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Fast and High-Quality Visibility Determination
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Computer generated imagery is vital to the entertainment industry in the production of games and films, for example. It is also increasingly important for visualization in design, architecture, engineering, and medicine, to name a few. Improvements to rendering techniques come from a combination of improved algorithms and more powerful hardware. Typically, hardware developments introduce new challenges and opportunities for algorithms that better fit the platform. Recently, these developments involve a widening gap between memory bandwidth and compute capabilities, wide SIMD units, and shared memory between CPU and GPU. The focus of this thesis is on improved algorithms for visibility queries that are used in graphics, motivated by challenges introduced by recent hardware developments. Geometry sampling lies at the core of rendering techniques, both for real-time and offline rendering, and generating images of higher quality generally involves taking more samples. Performance and quality improvements for visibility samples can thus enable higher quality rendering within a smaller time budget. This thesis presents five published papers with new solutions for visibility queries in the two major rendering paradigms in use today: rasterization and ray tracing. Two-dimensional rasterization is common in real-time graphics because of its computational efficiency. Multiple point samples are usually taken for each pixel to get high-quality images without aliasing artifacts. When rendering thin curves, many samples will typically be required to achieve acceptable quality. In this context, we propose that thin curves can be rasterized in high quality on a graphics processor using spatial line samples and curve-specific intersection tests. Further, we propose that the recent advent of shared memory between CPU and GPU can allow for MSAA computations to be offloaded to idle CPU cores. In three-dimensional rasterization, specifically rasterization with motion blur, we introduce a way to render practically noise- and alias-free images with competitive performance using semi-analytical line-based visibility queries on a multi-core CPU. Ray tracing, common in offline rendering, is a flexible rendering technique that can model how light propagates in a scene. Challenges in ray tracing include how a ray can be efficiently tested against a scene. Tests are accelerated by building a spatial hierarchy over the scene and our work in ray tracing specifically targets the process of traversing rays against a bounding volume hierarchy (BVH). The first contribution involves a flexible BVH traversal algorithm that executes without storing the traversal state in a stack, which may be beneficial in cases where storing a stack is expensive. The second contribution is an efficient algorithm for traversing large streams of rays against a BVH while making use of wide SIMD.
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| 5. |
- Barringer, Rasmus, et al.
(author)
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High-Quality Curve Rendering using Line Sampled Visibility
- 2012
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In: ACM Transactions on Graphics. - : Association for Computing Machinery (ACM). - 0730-0301 .- 1557-7368. ; 31:6, s. 162-162
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Journal article (peer-reviewed)abstract
- Computing accurate visibility for thin primitives, such as hair strands, fur, grass, at all scales remains difficult or expensive. To that end, we present an efficient visibility algorithm based on spatial line sampling, and a novel intersection algorithm between line sample planes and Bezier splines with varying thickness. Our algorithm produces accurate visibility both when the projected width of the curve is a tiny fraction of a pixel, and when the projected width is tens of pixels. In addition, we present a rapid resolve procedure that computes final visibility. Using an optimized implementation running on graphics processors, we can render tens of thousands long hair strands with noise-free visibility at near-interactive rates.
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| 6. |
- Ganestam, Per, et al.
(author)
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Bonsai: Rapid Bounding Volume Hierarchy Generation using Mini Trees
- 2015
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In: Journal of Computer Graphics Techniques. - 2331-7418. ; 4:3, s. 23-42
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Journal article (peer-reviewed)abstract
- We present an algorithm, called Bonsai, for rapidly building bounding volume hierarchies for ray tracing. Our method starts by computing midpoints of the triangle bounding boxes and then performs a rough hierarchical top-down split using the midpoints, creating triangle groups with tight bounding boxes. For each triangle group, a mini tree is built using an improved sweep SAH method. Once all mini trees have been built, we use them as leaves when building the top tree of the bounding volume hierarchy. We also introduce a novel and inexpensive optimization technique, called mini-tree pruning, that can be used to detect and improve poorly built parts of the tree. We achieve a little better than 100% in ray-tracing performance compared to a "ground truth" greedy top-down sweep SAH method, and our build times are the lowest we have seen with comparable tree quality.
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| 7. |
- Gribel, Carl Johan, et al.
(author)
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High-Quality Spatio-Temporal Rendering using Semi-Analytical Visibility
- 2011
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In: ACM Transactions on Graphics. - : Association for Computing Machinery (ACM). - 0730-0301 .- 1557-7368. ; 30:4, s. 1-54
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Conference paper (peer-reviewed)abstract
- We present a novel visibility algorithm for rendering motion blur with per-pixel anti-aliasing. Our algorithm uses a number of line samples over a rectangular group of pixels, and together with the time dimension, a two-dimensional spatio-temporal visibility problem needs to be solved per line sample. In a coarse culling step, our algorithm first uses a bounding volume hierarchy to rapidly remove geometry that do not overlap with the current line sample. For the remaining triangles, we approximate each triangle's depth function, along the line and along the time dimension, with a number of patch triangles. We resolve for the final color using an analytical visibility algorithm with depth sorting, simple occlusion culling, and clipping. Shading is decoupled from visibility, and we use a shading cache for efficient reuse of shaded values. In our results, we show practically noise-free renderings of motion blur with high-quality spatial anti-aliasing and with competitive rendering times. We also demonstrate that our algorithm, with some adjustments, can be used to accurately compute motion blurred ambient occlusion.
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