co-maps/tools/topography_generator/marching_squares/square.hpp

#pragma once

#include "topography_generator/marching_squares/contours_builder.hpp"

namespace topography_generator
{
template <typename ValueType>
class Square
{
public:
  Square(ValueType minValue, ValueType valueStep, std::string const & debugId)
    : m_minValue(minValue)
    , m_valueStep(valueStep)
    , m_debugId(debugId)
  {
    static_assert(std::is_integral<ValueType>::value && std::is_signed<ValueType>::value);
  }

  void Init(double left, double bottom, double right, double top, ValueType lb, ValueType rb, ValueType lt,
            ValueType rt, ValueType invalid)
  {
    m_isValid = true;

    m_left = left;
    m_bottom = bottom;
    m_right = right;
    m_top = top;

    m_valueLB = GetValue(lb, invalid);
    m_valueRB = GetValue(rb, invalid);
    m_valueLT = GetValue(lt, invalid);
    m_valueRT = GetValue(rt, invalid);
  }

  void GenerateSegments(ContoursBuilder & builder) const
  {
    if (!m_isValid)
      return;

    ValueType minVal = std::min(m_valueLB, std::min(m_valueLT, std::min(m_valueRT, m_valueRB)));
    ValueType maxVal = std::max(m_valueLB, std::max(m_valueLT, std::max(m_valueRT, m_valueRB)));

    ToLevelsRange(m_valueStep, minVal, maxVal);

    CHECK_GREATER_OR_EQUAL(minVal, m_minValue, (m_debugId));

    for (auto val = minVal; val < maxVal; val += m_valueStep)
      AddSegments(val, (val - m_minValue) / m_valueStep, builder);
  }

  static void ToLevelsRange(ValueType step, ValueType & minVal, ValueType & maxVal)
  {
    if (minVal > 0)
      minVal = step * ((minVal + step - 1) / step);
    else
      minVal = step * (minVal / step);

    if (maxVal > 0)
      maxVal = step * ((maxVal + step) / step);
    else
      maxVal = step * ((maxVal + 1) / step);
  }

private:
  enum class Rib
  {
    None,
    Left,
    Top,
    Right,
    Bottom,
    Unclear,
  };

  ValueType GetValue(ValueType val, ValueType invalid)
  {
    // If a contour goes right through the corner of the square false segments can be generated.
    // Shift the value slightly from the corner.
    if (val == invalid)
    {
      // LOG(LWARNING, ("Invalid value at the position", pos, m_debugId));
      m_isValid = false;
      return val;
    }

    if (abs(val) % m_valueStep == 0)
      return val + 1;
    return val;
  }

  void AddSegments(ValueType val, uint16_t ind, ContoursBuilder & builder) const
  {
    // Segment is a vector directed so that higher values is on the right.
    static std::pair<Rib, Rib> const intersectedRibs[] = {
        {Rib::None, Rib::None},        // 0000
        {Rib::Left, Rib::Bottom},      // 0001
        {Rib::Top, Rib::Left},         // 0010
        {Rib::Top, Rib::Bottom},       // 0011
        {Rib::Right, Rib::Top},        // 0100
        {Rib::Unclear, Rib::Unclear},  // 0101
        {Rib::Right, Rib::Left},       // 0110
        {Rib::Right, Rib::Bottom},     // 0111
        {Rib::Bottom, Rib::Right},     // 1000
        {Rib::Left, Rib::Right},       // 1001
        {Rib::Unclear, Rib::Unclear},  // 1010
        {Rib::Top, Rib::Right},        // 1011
        {Rib::Bottom, Rib::Top},       // 1100
        {Rib::Left, Rib::Top},         // 1101
        {Rib::Bottom, Rib::Left},      // 1110
        {Rib::None, Rib::None},        // 1111
    };

    uint8_t const pattern = (m_valueLB > val ? 1u : 0u) | ((m_valueLT > val ? 1u : 0u) << 1u) |
                            ((m_valueRT > val ? 1u : 0u) << 2u) | ((m_valueRB > val ? 1u : 0u) << 3u);

    auto const ribs = intersectedRibs[pattern];

    if (ribs.first == Rib::None)
      return;

    if (ribs.first != Rib::Unclear)
    {
      builder.AddSegment(ind, InterpolatePoint(ribs.first, val), InterpolatePoint(ribs.second, val));
    }
    else
    {
      auto const leftPos = InterpolatePoint(Rib::Left, val);
      auto const rightPos = InterpolatePoint(Rib::Right, val);
      auto const bottomPos = InterpolatePoint(Rib::Bottom, val);
      auto const topPos = InterpolatePoint(Rib::Top, val);

      ValueType const avVal = (m_valueLB + m_valueLT + m_valueRT + m_valueRB) / 4;
      if (avVal > val)
      {
        if (m_valueLB > val)
        {
          builder.AddSegment(ind, leftPos, topPos);
          builder.AddSegment(ind, rightPos, bottomPos);
        }
        else
        {
          builder.AddSegment(ind, bottomPos, leftPos);
          builder.AddSegment(ind, topPos, rightPos);
        }
      }
      else if (m_valueLB > val)
      {
        builder.AddSegment(ind, leftPos, bottomPos);
        builder.AddSegment(ind, rightPos, topPos);
      }
      else
      {
        builder.AddSegment(ind, topPos, leftPos);
        builder.AddSegment(ind, bottomPos, rightPos);
      }
    }
  }

  ms::LatLon InterpolatePoint(Square::Rib rib, ValueType val) const
  {
    double val1;
    double val2;
    double lat;
    double lon;

    switch (rib)
    {
    case Rib::Left:
      val1 = static_cast<double>(m_valueLB);
      val2 = static_cast<double>(m_valueLT);
      lon = m_left;
      break;
    case Rib::Right:
      val1 = static_cast<double>(m_valueRB);
      val2 = static_cast<double>(m_valueRT);
      lon = m_right;
      break;
    case Rib::Top:
      val1 = static_cast<double>(m_valueLT);
      val2 = static_cast<double>(m_valueRT);
      lat = m_top;
      break;
    case Rib::Bottom:
      val1 = static_cast<double>(m_valueLB);
      val2 = static_cast<double>(m_valueRB);
      lat = m_bottom;
      break;
    default: UNREACHABLE();
    }

    CHECK_NOT_EQUAL(val, val2, (m_debugId));
    double const coeff = (val1 - val) / (val - val2);

    switch (rib)
    {
    case Rib::Left:
    case Rib::Right: lat = (m_bottom + m_top * coeff) / (1 + coeff); break;
    case Rib::Bottom:
    case Rib::Top: lon = (m_left + m_right * coeff) / (1 + coeff); break;
    default: UNREACHABLE();
    }

    return {lat, lon};
  }

  double m_left;
  double m_right;
  double m_bottom;
  double m_top;

  ValueType m_valueLB;
  ValueType m_valueLT;
  ValueType m_valueRT;
  ValueType m_valueRB;

  ValueType m_minValue;
  ValueType m_valueStep;
  std::string m_debugId;

  bool m_isValid;
};
}  // namespace topography_generator