压感手写笔迹

Collect pointer events with pressure (fall back to simulated pressure from speed). Smooth points with an exponential moving average, then for each point compute a radius from pressure and a thinning factor. Offset each point along the perpendicular of the local direction by +radius and -radius to get left and right outlines, add tapered caps by shrinking radius over the first and last segments, and join left plus reversed right into one polygon. Render it as a filled SVG path using quadratic curves between midpoints for smoothness.