手绘草图图形库

Implement a seeded PRNG so drawings are stable across redraws. For a line, generate two cubic Bézier curves from start to end whose control points are offset perpendicular to the line by random amounts scaled by roughness and line length. For ellipses, sample points around the curve with jittered radius and an overshoot so the stroke does not close perfectly. For fills, compute hachure lines by intersecting parallel lines at an angle with the polygon edges, then draw each segment with the same jittered-line routine. Output either canvas paths or SVG path strings.