Polar Stroking: New Theory and Methods for Stroking Paths

TL;DR

This paper introduces a rigorous theoretical framework for stroking in vector graphics, along with a novel polar stroking method that improves rendering robustness and efficiency.

Contribution

It provides the first principled theory of stroking, enabling more accurate and efficient rendering of stroked paths in standards like PDF, SVG, and PostScript.

Findings

Developed a new polar stroking algorithm with bounded tessellation error

Achieved robust path rendering on modern GPUs

Enhanced efficiency in arc length accumulation for texturing and dashing

Abstract

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.