Text Reflow

Pretext measures the paragraph once per font size, so each frame only does line breaking. For every line band the circle's chord is computed, which leaves a left and a right segment; each segment is filled with the next run of text from layoutNextLineRange before y advances by one line height. Because y only moves once per band, lines can never overlap.

let cursor = START;
let y = startY;
while (!done && y < height + lh) {
  const segs = [];
  let blocked = false;
  if (r > 1) {
    const nearY = Math.min(Math.max(cy, y), y + lh);
    const dy = nearY - cy;
    if (Math.abs(dy) < r) {
      const half = Math.sqrt(r * r - dy * dy) + PAD;
      blocked = true;
      if (Math.min(x1, cx - half) - x0 >= minW) segs.push([x0, Math.min(x1, cx - half)]);
      if (x1 - Math.max(x0, cx + half) >= minW) segs.push([Math.max(x0, cx + half), x1]);
    }
  }
  if (!blocked) segs.push([x0, x1]);

  for (const [sx0, sx1] of segs) {
    const range = layoutNextLineRange(prepared, cursor, sx1 - sx0);
    if (!range) { done = true; break; }
    out.push({ text: materializeLineRange(prepared, range).text, x: sx0, y });
    cursor = range.end;
  }
  y += lh; // exactly one line height per band
}