Tracer::Tracer(QObject *parent)

                {"#9f086e"},

void Tracer::setPalette(const QList<QColor> &newPalette) {

void Tracer::start(const QString &fileName) {

  referenceImage_ = QImage{};

  referenceImage_.load(QUrl(fileName).toLocalFile());

  if (referenceImage_.isNull()) {

  for (int i = 0; i < 600; ++i) {

  const auto size = generation_.size();

  const auto keepSize = 10;

  const auto replaceSize = 50;

  const auto kept = generation_.mid(0, keepSize);

  generation_ = generation_.mid(0, size - replaceSize);

  for (int i = 0; i < replaceSize; ++i) {

    generation_.append(Solution{{32, 32}, palette_});

  }

  auto rg = QRandomGenerator::global();

  for (qsizetype i = 0; i < size; i += 4) {

    const auto first = rg->bounded(size);

    const auto second = rg->bounded(size);

    if (first != second) {

      generation_[first].crossover(generation_[second]);

    }

  }

  std::for_each(std::begin(generation_), std::end(generation_),

                [this](auto &s) { s.mutate(palette_); });

  std::for_each(std::begin(solutions_), std::end(solutions_),

                [this](const auto &fn) { QFile::remove(fn); });

  generation_.append(kept);

  for (auto &solution : generation_) {

    solution.render(newFileName());

    solution.calculateFitness(referenceImage_);

    solution.fitness += solution.cost() * 100;

  std::sort(std::begin(generation_), std::end(generation_),

            [](const auto &a, const auto &b) { return a.fitness < b.fitness; });

  std::for_each(std::begin(generation_) + size, std::end(generation_),

                [](const auto &s) { QFile::remove(s.fileName); });

  generation_.remove(size, kept.size());

  bestSolution_ = generation_[0].fitness;

  std::transform(std::begin(generation_), std::end(generation_),

                 std::back_inserter(solutions_),

                 [](const auto &a) { return a.fileName; });

  emit bestSolutionChanged();

Solution::Solution(QSizeF size, const QList<QColor> &palette) : size{size} {

  primitives = {Primitive(size, palette), Primitive(size, palette)};

void Solution::calculateFitness(const QImage &target) {

  QImage candidate{fileName};

  if (candidate.isNull()) {

    fitness = 1e32;

    return;

  }

  // Both images assumed same size, same format

  double diffSum = 0;

  int width = target.width();

  int height = target.height();

  for (int y = 0; y < height; ++y) {

    auto candScan = reinterpret_cast<const QRgb *>(candidate.scanLine(y));

    auto targScan = reinterpret_cast<const QRgb *>(target.scanLine(y));

    for (int x = 0; x < width; ++x) {

      // Compare RGBA channels

      const QRgb cPix = candScan[x];

      const QRgb tPix = targScan[x];

      // const auto ca = qAlpha(cPix) / 255.0;

      const auto ta = qAlpha(tPix) / 255.0;

      const auto dr = qRed(cPix) - qRed(tPix);

      const auto dg = qGreen(cPix) - qGreen(tPix);

      const auto db = qBlue(cPix) - qBlue(tPix);

      const auto da = qAlpha(cPix) - qAlpha(tPix);

      diffSum +=

          qMax(qMax(qMax(dr * dr, dg * dg), db * db) * ta, da * da * 1.0);

    }

  }

  fitness = diffSum;

}

void Solution::render(const QString &fileName) {

  this->fileName = fileName;

  for (const auto &primitive : primitives) {

void Solution::mutate(const QList<QColor> &palette) {

  if (primitives.isEmpty()) {

    return;

  }

  auto rg = QRandomGenerator::global();

  double mutationRate = 0.05;

  if (rg->bounded(1.0) > mutationRate) {

    return;

  }

  for (auto &prim : primitives) {

    // Pen width

    if (rg->bounded(1.0) < mutationRate) {

      prim.pen.setWidthF(prim.pen.widthF() * (rg->bounded(1.5) + 0.5) + 0.05);

    }

    // Origin

    if (rg->bounded(1.0) < mutationRate) {

      prim.origin += QPointF(rg->bounded(10.0) - 5.0, rg->bounded(10.0) - 5.0);

    }

    if (prim.type == Polygon) {

      // Points

      for (auto &pt : prim.points) {

        if (rg->bounded(1.0) < mutationRate) {

          prim.origin +=

              QPointF(rg->bounded(10.0) - 5.0, rg->bounded(10.0) - 5.0);

        }

      }

    } else {  // Circle/ellipse

      if (rg->bounded(1.0) < mutationRate) {

        prim.radius1 *= rg->bounded(0.4) + 0.8;

      }

      if (rg->bounded(1.0) < mutationRate) {

        prim.radius2 *= rg->bounded(0.4) + 0.8;

      }

      if (rg->bounded(1.0) < mutationRate) {

        prim.rotation = rg->bounded(90.0);

      }

    }

  }

  if (rg->bounded(1.0) < mutationRate) {

    auto i = rg->bounded(primitives.size());

    Primitive p{size, palette};

    primitives.insert(i, p);

  }

  if (rg->bounded(1.0) < mutationRate) {

    auto i = rg->bounded(primitives.size());

    primitives.remove(i);

  }

}

void Solution::crossover(Solution &other) {

  const auto n = qMin(primitives.size(), other.primitives.size());

  auto rg = QRandomGenerator::global();

  if (rg->bounded(1.0) < 0.02) {

    if (n <= 1) {

      return;

    }

    // swap tails

    const auto cp = rg->bounded(1, primitives.size());

    const auto ocp = rg->bounded(1, other.primitives.size());

    const auto tail = primitives.mid(cp);

    const auto otherTail = other.primitives.mid(ocp);

    primitives.remove(cp, primitives.size() - cp);

    other.primitives.remove(ocp, other.primitives.size() - ocp);

    primitives.append(otherTail);

    other.primitives.append(tail);

  } else {

    if (n < 1) {

      return;

    }

    // swap one element

    const auto cp = rg->bounded(primitives.size());

    const auto ocp = rg->bounded(other.primitives.size());

    qSwap(primitives[cp], other.primitives[ocp]);

  }

}

Primitive::Primitive(QSizeF size, const QList<QColor> &palette) {

    radius1 = rg->bounded(size.width() * 0.2) + 2;

    radius2 = rg->bounded(size.width() * 0.2) + 2;