Table Of Links
ABSTRACT
1 INTRODUCTION
2 FLATTENING AND ARC APPROXIMATION OF CURVES
3 EULER SPIRALS AND THEIR PARALLEL CURVES
4 FLATTENED PARALLEL CURVES
5 ERROR METRICS FOR APPROXIMATION BY ARCS
6 EVOLUTES
7 CONVERSION FROM CUBIC BÉZIERS TO EULER SPIRALS
8 GPU IMPLEMENTATION
9 RESULTS
CONCLUSIONS, FUTURE WORK AND REFERENCES
10 CONCLUSIONS
Path stroking has received attention in recent years, with Nehab [2020] and Kilgard [2020b] both having proposed a complete theory of correct stroking in vector graphics. While there are a number of implementations of path filling on the GPU, the goal of also implementing stroke expansion on the GPU had not yet been realized. Building upon the theory proposed by Nehab [2020], we implemented an approach to stroke expansion that is GPU-friendly, and achieves high performance on commodity hardware.
We present the Euler spiral as an intermediate representation for a fast and precise approximation of both filled and stroked Bézier paths. Our method for lowering to both line and arc primitives avoids recursion and minimizes divergence, potentially serious problems for parallel evaluation on the GPU.
We propose a novel error metric to directly estimate approximation error as opposed to the commonly employed cut-then-measure approaches which often consume the lion’s share of computational expense. Our approach includes an efficient encoding scheme that alleviates the need for expensive CPU pre-computations and unlocks fully GPU-driven rendering of the entire vector graphics model.
FUTURE WORK
• The GPU implementation sequentializes some work that could be parallel, and is thus not as well load-balanced as it might be. An appealing future direction is to split the pipeline into separate stages, executed by the GPU as nodes in a work graph [21]. This structure is appealing because load balancing is done by hardware.
• The pre-allocation requirement for bump-allocated line soup buffer is a limitation due to today’s graphics APIs. A more accurate and optimized buffer size estimation heuristic is considered future work. It may also be interesting to explore whether graphics APIs can be extended to facilitate GPU-driven scheduling of the compute workload under a bounded memory footprint.
• Many of the error metrics were empirically determined. The mathematical theory behind them should be developed more rigorously, and that process will likely uncover opportunities to fine-tune the technique.
• As mentioned earlier, we did not have time to sufficiently explore a pipeline architecture for GPU-based dashing. Given its parameterization by arc length, we believe the Euler spiral representation lends itself well to an approach based on parallel prefix sums of segment arc lengths.
REFERENCES
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Authors:
- Raph Levien
- Arman Uguray
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This paper is available on arxiv under CC 4.0 license.
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