Polar Stroking: New Theory and Methods for Stroking Paths
This work addresses a foundational gap in vector graphics rendering for developers and standards bodies, though it is incremental in providing a new method rather than a paradigm shift.
The paper tackles the lack of a rigorous theory for stroking paths in vector graphics standards like PDF and SVG, developing a principled theory and a novel polar stroking method that robustly renders stroked paths with bounded tessellation error without recursion.
Stroking and filling are the two basic rendering operations on paths in vector graphics. The theory of filling a path is well-understood in terms of contour integrals and winding numbers, but when path rendering standards specify stroking, they resort to the analogy of painting pixels with a brush that traces the outline of the path. This means important standards such as PDF, SVG, and PostScript lack a rigorous way to say what samples are inside or outside a stroked path. Our work fills this gap with a principled theory of stroking. Guided by our theory, we develop a novel polar stroking method to render stroked paths robustly with an intuitive way to bound the tessellation error without needing recursion. Because polar stroking guarantees small uniform steps in tangent angle, it provides an efficient way to accumulate arc length along a path for texturing or dashing. While this paper focuses on developing the theory of our polar stroking method, we have successfully implemented our methods on modern programmable GPUs.