Проективное преобразование (поиск относительного положения точки)

import 'package:image/image.dart' as imglib;

class PerspectiveRectifier {
  late num a, b, c;
  late num a1, b1, c1;
  late num d, e, f;

  PerspectiveRectifier(imglib.Point topLeft, imglib.Point topRight,
      imglib.Point bottomLeft, imglib.Point bottomRight) {
    final x1 = topLeft.x;
    final y1 = topLeft.y;
    final x2 = topRight.x;
    final y2 = topRight.y;
    final x3 = bottomRight.x;
    final y3 = bottomRight.y;
    final x4 = bottomLeft.x;
    final y4 = bottomLeft.y;

    a = ((y4 - y3) * (x1 + x3 - x2 - x4) - (x4 - x3) * (y1 + y3 - y2 - y4)) /
        ((y4 - y3) * (x2 - x3) - (x4 - x3) * (y2 - y3));
    b = (x1 + x3 - x2 - x4 - (x2 - x3) * a) / (x4 - x3);
    c = 1;
    a1 = x2 * a + x2 - x1;
    b1 = x4 * b + x4 - x1;
    c1 = x1;
    d = y2 * a + y2 - y1;
    e = y4 * b + y4 - y1;
    f = y1;
  }

  Offset calculateSourceOffset(Offset relativeTargetOffset) {
    return Offset(
        (a1 * relativeTargetOffset.dx + b1 * relativeTargetOffset.dy + c1) /
            (a * relativeTargetOffset.dx + b * relativeTargetOffset.dy + c),
        (d * relativeTargetOffset.dx + e * relativeTargetOffset.dy + f) /
            (a * relativeTargetOffset.dx + b * relativeTargetOffset.dy + c));
  }
}

  imglib.Image copyRectifyWithPerspectiveCorrection(
      imglib.Image src, PerspectiveRectifier r, imglib.Image? toImage) {
    final dst = toImage ?? imglib.Image.from(src);

    for (int y = 0; y < dst.height; ++y) {
      for (int x = 0; x < dst.width; ++x) {
        final srsOffset =
            r.calculateSourceOffset(Offset(x / dst.width, y / dst.height));
        final srcPixel =
            src.isBoundsSafe(srsOffset.dx.toInt(), srsOffset.dy.toInt())
                ? src.getPixel(srsOffset.dx.toInt(), srsOffset.dy.toInt())
                : src.getColor(0, 0, 0);
        dst.setPixel(x, y, srcPixel);
      }
    }
    return dst;
  }