Function interpolateSpline

web/js/sparse_track_editor.js:26–53

(controlPoints, numSamples)

}

function interpolateSpline(controlPoints, numSamples) {
  if (controlPoints.length === 0) return [];
  if (controlPoints.length === 1) {
    return Array.from({ length: numSamples }, () => ({ ...controlPoints[0] }));
  }
  if (controlPoints.length === 2) {
    const [a, b] = controlPoints;
    return Array.from({ length: numSamples }, (_, i) => {
      const t = i / (numSamples - 1);
      return { x: a.x + (b.x - a.x) * t, y: a.y + (b.y - a.y) * t };
    });
  }
  // Pad with phantom endpoints for Catmull-Rom
  const pts = [
    controlPoints[0],
    ...controlPoints,
    controlPoints[controlPoints.length - 1],
  ];
  const nSeg = pts.length - 3;
  const result = [];
  for (let i = 0; i < numSamples; i++) {
    const gT = (i / (numSamples - 1)) * nSeg;
    const seg = Math.min(Math.floor(gT), nSeg - 1);
    const lT = gT - seg;
    result.push(catmullRom(pts[seg], pts[seg + 1], pts[seg + 2], pts[seg + 3], lT));
  }
  return result;
}

// ---------------------------------------------------------------------------
// Visual constants