qgselevationmap.cpp

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/***************************************************************************
  qgselevationmap.cpp
  --------------------------------------
  Date                 : August 2022
  Copyright            : (C) 2022 by Martin Dobias
  Email                : wonder dot sk at gmail dot com
 ***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/
 
#include "qgselevationmap.h"
 
#include <algorithm>
#include <cmath>
#include <memory>
 
#include "qgsrasterblock.h"
 
#include <QPainter>
#include <QString>
 
using namespace Qt::StringLiterals;
 
static const int ELEVATION_OFFSET = 7900;
static const int ELEVATION_SCALE = 1000;
 
 
QgsElevationMap::QgsElevationMap( const QSize &size, float devicePixelRatio )
  : mElevationImage( size, QImage::Format_ARGB32 )
{
  mElevationImage.fill( 0 );
  mElevationImage.setDevicePixelRatio( devicePixelRatio );
}
 
QgsElevationMap::QgsElevationMap( const QImage &image )
  : mElevationImage( image )
{}
 
QgsElevationMap::QgsElevationMap( const QgsElevationMap &other )
  : mElevationImage( other.mElevationImage )
{
  mPainter.reset();
}
 
QRgb QgsElevationMap::encodeElevation( float z )
{
  double zScaled = ( z + ELEVATION_OFFSET ) * ELEVATION_SCALE;
  unsigned int zInt = static_cast<unsigned int>( std::clamp( zScaled, 0., 16777215. ) ); // make sure to fit into 3 bytes
  return QRgb( zInt | ( static_cast< unsigned int >( 0xff ) << 24 ) );
}
 
float QgsElevationMap::decodeElevation( QRgb colorRaw )
{
  unsigned int zScaled = colorRaw & 0xffffff;
  return ( ( float ) zScaled ) / ELEVATION_SCALE - ELEVATION_OFFSET;
}
 
std::unique_ptr<QgsElevationMap> QgsElevationMap::fromRasterBlock( QgsRasterBlock *block )
{
  auto elevMap = std::make_unique<QgsElevationMap>( QSize( block->width(), block->height() ) );
  QRgb *dataPtr = reinterpret_cast<QRgb *>( elevMap->mElevationImage.bits() );
  for ( int row = 0; row < block->height(); ++row )
  {
    for ( int col = 0; col < block->width(); ++col )
    {
      bool isNoData;
      double value = block->valueAndNoData( row, col, isNoData );
      if ( !isNoData )
        *dataPtr = encodeElevation( static_cast<float>( value ) );
      ++dataPtr;
    }
  }
  return elevMap;
}
 
QgsElevationMap &QgsElevationMap::operator=( const QgsElevationMap &other )
{
  if ( &other == this )
    return *this;
 
  mPainter.reset();
  mElevationImage = other.mElevationImage;
  return *this;
}
 
void QgsElevationMap::applyEyeDomeLighting( QImage &img, int distance, float strength, float rendererScale ) const
{
  const int imgWidth = img.width(), imgHeight = img.height();
  QRgb *imgPtr = reinterpret_cast<QRgb *>( img.bits() );
  const QRgb *elevPtr = reinterpret_cast<const QRgb *>( mElevationImage.constBits() );
 
  const int neighbours[] = { -1, 0, 1, 0, 0, -1, 0, 1 };
  for ( int i = 0; i < imgWidth; ++i )
  {
    for ( int j = 0; j < imgHeight; ++j )
    {
      qgssize index = j * static_cast<qgssize>( imgWidth ) + i;
      float factor = 0.0f;
      float centerDepth = decodeElevation( elevPtr[index] );
      if ( isNoData( elevPtr[index] ) )
        continue;
      for ( qgssize k = 0; k < 4; ++k )
      {
        float borderFactor = 1.0f;
        int iNeighbour = std::clamp( i + distance * neighbours[2 * k], 0, imgWidth - 1 );
        int jNeighbour = std::clamp( j + distance * neighbours[2 * k + 1], 0, imgHeight - 1 );
        qgssize neighbourIndex = jNeighbour * static_cast<qgssize>( imgWidth ) + iNeighbour;
 
        // neighbour is no data, we try to reach one pixel closer that is not no data
        // and calculate a factor to take account of the reduction of the distance
        if ( isNoData( elevPtr[neighbourIndex] ) )
        {
          if ( neighbours[2 * k] != 0 )
          {
            int corrI = iNeighbour;
            int inc = neighbours[2 * k];
            while ( corrI != i && isNoData( elevPtr[neighbourIndex] ) )
            {
              corrI -= inc;
              neighbourIndex = jNeighbour * static_cast<qgssize>( imgWidth ) + corrI;
            }
            if ( corrI == i )
              continue;
 
            borderFactor = static_cast<float>( distance ) / static_cast<float>( std::abs( i - corrI ) );
          }
 
          if ( neighbours[2 * k + 1] != 0 )
          {
            int corrJ = jNeighbour;
            int inc = neighbours[2 * k + 1];
            while ( corrJ != j && isNoData( elevPtr[neighbourIndex] ) )
            {
              corrJ -= inc;
              neighbourIndex = corrJ * static_cast<qgssize>( imgWidth ) + iNeighbour;
            }
            if ( corrJ == j )
              continue;
 
            borderFactor = static_cast<float>( distance ) / static_cast<float>( std::abs( j - corrJ ) );
          }
        }
 
        // neighbour is outside the extent (right or left), we take the pixel on border
        // and calculate a factor to take account of the reduction of the distance
        if ( neighbours[2 * k] != 0 && std::abs( iNeighbour - i ) < distance )
        {
          if ( i > iNeighbour )
            borderFactor = static_cast<float>( distance ) / static_cast<float>( i );
          else if ( i < iNeighbour )
            borderFactor = static_cast<float>( distance ) / static_cast<float>( ( imgWidth - i - 1 ) );
        }
        if ( neighbours[2 * k + 1] != 0 && std::abs( jNeighbour - j ) < distance )
        {
          if ( j > jNeighbour )
            borderFactor = static_cast<float>( distance ) / static_cast<float>( j );
          else if ( j < jNeighbour )
            borderFactor = static_cast<float>( distance ) / static_cast<float>( imgHeight - j - 1 );
        }
 
        float neighbourDepth = decodeElevation( elevPtr[neighbourIndex] );
        factor += std::max<float>( 0, -( centerDepth - neighbourDepth ) * borderFactor );
      }
      float shade = expf( -factor * strength / rendererScale );
 
      QRgb c = imgPtr[index];
      imgPtr[index]
        = qRgba( static_cast<int>( static_cast<float>( qRed( c ) ) * shade ), static_cast<int>( static_cast<float>( qGreen( c ) ) * shade ), static_cast<int>( static_cast<float>( qBlue( c ) ) * shade ), qAlpha( c ) );
    }
  }
}
 
void QgsElevationMap::applyHillshading( QImage &img, bool multiDirectional, double altitude, double azimuth, double zFactor, double cellSizeX, double cellSizeY ) const
{
  // algs from  src/raster/qgshillshaderenderer.cpp
  double altRad = altitude * M_PI / 180.0;
  double cos_altRadian = std::cos( altRad );
  double sin_altRadian = std::sin( altRad );
  double cos_alt_mul_z = cos_altRadian * zFactor;
  double azimuthRad = -1 * azimuth * M_PI / 180.0;
  double cos_az_mul_cos_alt_mul_z = std::cos( azimuthRad ) * cos_alt_mul_z;
  double sin_az_mul_cos_alt_mul_z = std::sin( azimuthRad ) * cos_alt_mul_z;
 
  // From qgshillshaderenderer.cpp, -32.87001872802012 comes from ( 127.0 * std::cos(225.0 *  M_PI / 180.0))
  // but this expression actually equals -89.8025612106916. To be consistent, we keep -32.87001872802012
  // and divide it by 254 because, here, values are between 0.0 and 1.0, not between 0 and 255
  double cos225_az_mul_cos_alt_mul_z_mul_0_5 = -32.87001872802012 * cos_alt_mul_z / 255;
  double square_z = zFactor * zFactor;
 
  QRgb *imgPtr = reinterpret_cast<QRgb *>( img.bits() );
  const QRgb *elevPtr = reinterpret_cast<const QRgb *>( mElevationImage.constBits() );
 
  const int imgWidth = img.width(), imgHeight = img.height();
 
  auto colRowToIndex = [&]( int c, int r ) -> qgssize { return static_cast<qgssize>( r ) * imgWidth + c; };
 
  float noData = noDataValue();
 
  // Elevation value matrix
  // 0 1 2   11 12 13
  // 3 4 5   21 22 23
  // 6 7 8   31 32 33
  float pixelValues[9];
 
  for ( int rowC = 0; rowC < imgHeight; ++rowC )
  {
    int rowU = std::max( 0, rowC - 1 );
    int rowD = std::min( imgHeight - 1, rowC + 1 );
 
    pixelValues[1] = decodeElevation( elevPtr[colRowToIndex( 0, rowU )] );
    pixelValues[4] = decodeElevation( elevPtr[colRowToIndex( 0, rowC )] );
    pixelValues[7] = decodeElevation( elevPtr[colRowToIndex( 0, rowD )] );
 
    pixelValues[2] = decodeElevation( elevPtr[colRowToIndex( 1, rowU )] );
    pixelValues[5] = decodeElevation( elevPtr[colRowToIndex( 1, rowC )] );
    pixelValues[8] = decodeElevation( elevPtr[colRowToIndex( 1, rowD )] );
 
 
    for ( int colC = 0; colC < imgWidth; ++colC )
    {
      qgssize centerIndex = colRowToIndex( colC, rowC );
      int colR = std::min( imgWidth - 1, colC + 1 );
 
      pixelValues[0] = pixelValues[1];
      pixelValues[3] = pixelValues[4];
      pixelValues[6] = pixelValues[7];
 
      pixelValues[1] = pixelValues[2];
      pixelValues[4] = pixelValues[5];
      pixelValues[7] = pixelValues[8];
 
      pixelValues[2] = decodeElevation( elevPtr[colRowToIndex( colR, rowU )] );
      pixelValues[5] = decodeElevation( elevPtr[colRowToIndex( colR, rowC )] );
      pixelValues[8] = decodeElevation( elevPtr[colRowToIndex( colR, rowD )] );
 
      if ( elevPtr[centerIndex] != 0 )
      {
        // This is center cell. Use this in place of nodata neighbors
        const float x22 = pixelValues[4];
        if ( x22 == noData )
          continue;
 
        const float x11 = ( pixelValues[0] == noData ) ? x22 : pixelValues[0];
        const float x21 = ( pixelValues[3] == noData ) ? x22 : pixelValues[3];
        const float x31 = ( pixelValues[6] == noData ) ? x22 : pixelValues[6];
 
        const float x12 = ( pixelValues[1] == noData ) ? x22 : pixelValues[1];
        const float x32 = ( pixelValues[7] == noData ) ? x22 : pixelValues[7];
 
        const float x13 = ( pixelValues[2] == noData ) ? x22 : pixelValues[2];
        const float x23 = ( pixelValues[5] == noData ) ? x22 : pixelValues[5];
        const float x33 = ( pixelValues[8] == noData ) ? x22 : pixelValues[8];
 
        const double derX = static_cast<double>( ( x13 + x23 + x23 + x33 ) - ( x11 + x21 + x21 + x31 ) ) / ( 8 * cellSizeX );
        const double derY = static_cast<double>( ( x31 + x32 + x32 + x33 ) - ( x11 + x12 + x12 + x13 ) ) / ( 8 * -cellSizeY );
 
        double shade = 0;
        if ( !multiDirectional )
        {
          // Standard single direction hillshade
          shade = std::clamp( ( sin_altRadian - ( derY * cos_az_mul_cos_alt_mul_z - derX * sin_az_mul_cos_alt_mul_z ) ) / std::sqrt( 1 + square_z * ( derX * derX + derY * derY ) ), 0.0, 1.0 );
        }
        else
        {
          // Weighted multi direction as in http://pubs.usgs.gov/of/1992/of92-422/of92-422.pdf
          // Fast formula from GDAL DEM
          const double xx = derX * derX;
          const double yy = derY * derY;
          const double xx_plus_yy = xx + yy;
          // Flat?
          if ( xx_plus_yy == 0.0 )
          {
            shade = std::clamp( sin_altRadian, 0.0, 1.0 );
          }
          else
          {
            // ... then the shade value from different azimuth
            double val225_mul_0_5 = sin_altRadian * 0.5 + ( derX - derY ) * cos225_az_mul_cos_alt_mul_z_mul_0_5;
            val225_mul_0_5 = ( val225_mul_0_5 <= 0.0 ) ? 0.0 : val225_mul_0_5;
            double val270_mul_0_5 = sin_altRadian * 0.5 - derX * cos_alt_mul_z * 0.5;
            val270_mul_0_5 = ( val270_mul_0_5 <= 0.0 ) ? 0.0 : val270_mul_0_5;
            double val315_mul_0_5 = sin_altRadian * 0.5 + ( derX + derY ) * cos225_az_mul_cos_alt_mul_z_mul_0_5;
            val315_mul_0_5 = ( val315_mul_0_5 <= 0.0 ) ? 0.0 : val315_mul_0_5;
            double val360_mul_0_5 = sin_altRadian * 0.5 - derY * cos_alt_mul_z * 0.5;
            val360_mul_0_5 = ( val360_mul_0_5 <= 0.0 ) ? 0.0 : val360_mul_0_5;
 
            // ... then the weighted shading
            const double weight_225 = 0.5 * xx_plus_yy - derX * derY;
            const double weight_270 = xx;
            const double weight_315 = xx_plus_yy - weight_225;
            const double weight_360 = yy;
            const double cang_mul_127 = ( ( weight_225 * val225_mul_0_5 + weight_270 * val270_mul_0_5 + weight_315 * val315_mul_0_5 + weight_360 * val360_mul_0_5 ) / xx_plus_yy )
                                        / ( 1 + square_z * xx_plus_yy );
 
            shade = std::clamp( cang_mul_127, 0.0, 1.0 );
          }
        }
 
        QRgb c = imgPtr[centerIndex];
        imgPtr[centerIndex]
          = qRgba( static_cast<int>( static_cast<float>( qRed( c ) ) * shade ), static_cast<int>( static_cast<float>( qGreen( c ) ) * shade ), static_cast<int>( static_cast<float>( qBlue( c ) ) * shade ), qAlpha( c ) );
      }
    }
  }
}
 
QPainter *QgsElevationMap::painter() const
{
  if ( !mPainter )
  {
    mPainter = std::make_unique<QPainter>();
    mPainter->begin( &mElevationImage );
  }
  return mPainter.get();
}
 
void QgsElevationMap::combine( const QgsElevationMap &otherElevationMap, Qgis::ElevationMapCombineMethod method )
{
  if ( otherElevationMap.mElevationImage.size() != mElevationImage.size() )
  {
    QgsDebugMsgLevel( u"Elevation map with different sizes can not be combined"_s, 4 );
    return;
  }
 
  QRgb *elevPtr = reinterpret_cast<QRgb *>( mElevationImage.bits() );
  const QRgb *otherElevPtr = reinterpret_cast<const QRgb *>( otherElevationMap.mElevationImage.constBits() );
 
  int width = mElevationImage.width();
  int height = mElevationImage.height();
 
  for ( int row = 0; row < height; ++row )
  {
    for ( int col = 0; col < width; ++col )
    {
      qgssize index = col + static_cast<qgssize>( row ) * width;
      if ( !isNoData( otherElevPtr[index] ) )
      {
        switch ( method )
        {
          case Qgis::ElevationMapCombineMethod::HighestElevation:
          {
            double elev = decodeElevation( elevPtr[index] );
            double otherElev = decodeElevation( otherElevPtr[index] );
            if ( otherElev > elev )
              elevPtr[index] = otherElevPtr[index];
          }
          break;
          case Qgis::ElevationMapCombineMethod::NewerElevation:
            elevPtr[index] = otherElevPtr[index];
            break;
        }
      }
    }
  }
}
 
 
bool QgsElevationMap::isValid() const
{
  return !mElevationImage.isNull();
}
 
void QgsElevationMap::fillWithRasterBlock( QgsRasterBlock *block, int top, int left, double zScale, double offset )
{
  QRgb *dataPtr = reinterpret_cast<QRgb *>( mElevationImage.bits() );
 
  int widthMap = mElevationImage.width();
  int heightMap = mElevationImage.height();
  int widthBlock = block->width();
  int combinedHeight = std::min( mElevationImage.height(), block->height() + top );
  int combinedWidth = std::min( widthMap, widthBlock + left );
  for ( int row = std::max( 0, top ); row < combinedHeight; ++row )
  {
    if ( row >= heightMap )
      continue;
 
    for ( int col = std::max( 0, left ); col < combinedWidth; ++col )
    {
      if ( col >= widthMap )
        continue;
 
      bool isNoData = true;
      double value = block->valueAndNoData( ( row - top ), ( col - left ), isNoData );
      qgssize index = col + static_cast<qgssize>( row ) * widthMap;
      if ( isNoData )
        dataPtr[index] = 0;
      else
        dataPtr[index] = encodeElevation( static_cast<float>( value * zScale + offset ) );
    }
  }
}