Binary search for point on path (https://stackoverflow.com/q/72764799/6509751)

main.dart

import 'dart:math';
import 'dart:ui';

void main() {
  final path = Path();
  path.moveTo(0, 200);
  path.lineTo(10, 210);
  path.lineTo(30, 190);
  path.lineTo(55, 150);
  path.lineTo(80, 205);
  path.lineTo(100, 0);
  
  const searchDx = 75;
  const iterations = 20;
  
  final pathMetric = path.computeMetrics().first;
  final pathDistance = pathMetric.length;
  late Offset closestOffset;
  var closestDistance = pathDistance / 2;
  for (var n = 1; n <= iterations; n++) {
    closestOffset = pathMetric.getTangentForOffset(closestDistance)!.position;
    if (closestOffset.dx == searchDx) break;
    
    final change = pathDistance / pow(2, n);
    if (closestOffset.dx < searchDx) {
      closestDistance += change;
    } else {
      closestDistance -= change;
    }
  }
  
  print(closestOffset);
}