/******************************************************************************
 *
 * Project:  Virtual GDAL Datasets
 * Purpose:  Implementation of VRTSimpleSource, VRTFuncSource and
 *           VRTAveragedSource.
 * Author:   Frank Warmerdam <warmerdam@pobox.com>
 *
 ******************************************************************************
 * Copyright (c) 2001, Frank Warmerdam <warmerdam@pobox.com>
 * Copyright (c) 2008-2013, Even Rouault <even dot rouault at mines-paris dot org>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 ****************************************************************************/

#include "gdal_vrt.h"
#include "vrtdataset.h"

#include <climits>
#include <cmath>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <limits>
#include <string>

#include "cpl_conv.h"
#include "cpl_error.h"
#include "cpl_hash_set.h"
#include "cpl_minixml.h"
#include "cpl_progress.h"
#include "cpl_string.h"
#include "cpl_vsi.h"
#include "gdal.h"
#include "gdal_priv.h"
#include "gdal_proxy.h"
#include "gdal_priv_templates.hpp"

/*! @cond Doxygen_Suppress */

// #define DEBUG_VERBOSE 1

// See #5459
#ifdef isnan
#define HAS_ISNAN_MACRO
#endif
#include <algorithm>
#if defined(HAS_ISNAN_MACRO) && !defined(isnan)
#define isnan std::isnan
#endif

CPL_CVSID("$Id: vrtsources.cpp 7601a637dfd204948d00f4691c08f02eb7584de5 2019-04-12 04:29:21 -0500 Norman Barker $")

/************************************************************************/
/* ==================================================================== */
/*                             VRTSource                                */
/* ==================================================================== */
/************************************************************************/

VRTSource::~VRTSource() {}

/************************************************************************/
/*                             GetFileList()                            */
/************************************************************************/

void VRTSource::GetFileList(char*** /* ppapszFileList */,
                            int * /* pnSize */,
                            int * /* pnMaxSize */,
                            CPLHashSet * /* hSetFiles */)
{}

/************************************************************************/
/* ==================================================================== */
/*                          VRTSimpleSource                             */
/* ==================================================================== */
/************************************************************************/

/************************************************************************/
/*                          VRTSimpleSource()                           */
/************************************************************************/

VRTSimpleSource::VRTSimpleSource() :
    m_poRasterBand(nullptr),
    m_poMaskBandMainBand(nullptr),
    m_dfSrcXOff(0.0),
    m_dfSrcYOff(0.0),
    m_dfSrcXSize(0.0),
    m_dfSrcYSize(0.0),
    m_dfDstXOff(0.0),
    m_dfDstYOff(0.0),
    m_dfDstXSize(0.0),
    m_dfDstYSize(0.0),
    m_bNoDataSet(FALSE),
    m_dfNoDataValue(VRT_NODATA_UNSET),
    m_nMaxValue(0),
    m_bRelativeToVRTOri(-1),
    m_nExplicitSharedStatus(-1)
{}

/************************************************************************/
/*                          VRTSimpleSource()                           */
/************************************************************************/

VRTSimpleSource::VRTSimpleSource( const VRTSimpleSource* poSrcSource,
                                  double dfXDstRatio, double dfYDstRatio ) :
    m_poRasterBand(poSrcSource->m_poRasterBand),
    m_poMaskBandMainBand(poSrcSource->m_poMaskBandMainBand),
    m_dfSrcXOff(poSrcSource->m_dfSrcXOff),
    m_dfSrcYOff(poSrcSource->m_dfSrcYOff),
    m_dfSrcXSize(poSrcSource->m_dfSrcXSize),
    m_dfSrcYSize(poSrcSource->m_dfSrcYSize),
    m_dfDstXOff(poSrcSource->m_dfDstXOff * dfXDstRatio),
    m_dfDstYOff(poSrcSource->m_dfDstYOff * dfYDstRatio),
    m_dfDstXSize(poSrcSource->m_dfDstXSize * dfXDstRatio),
    m_dfDstYSize(poSrcSource->m_dfDstYSize * dfYDstRatio),
    m_bNoDataSet(poSrcSource->m_bNoDataSet),
    m_dfNoDataValue(poSrcSource->m_dfNoDataValue),
    m_nMaxValue(poSrcSource->m_nMaxValue),
    m_bRelativeToVRTOri(-1),
    m_nExplicitSharedStatus(poSrcSource->m_nExplicitSharedStatus)
{}

/************************************************************************/
/*                          ~VRTSimpleSource()                          */
/************************************************************************/

VRTSimpleSource::~VRTSimpleSource()

{
    if( m_poMaskBandMainBand != nullptr )
    {
        if( m_poMaskBandMainBand->GetDataset() != nullptr )
        {
            m_poMaskBandMainBand->GetDataset()->ReleaseRef();
        }
    }
    else if( m_poRasterBand != nullptr && m_poRasterBand->GetDataset() != nullptr )
    {
        m_poRasterBand->GetDataset()->ReleaseRef();
    }
}

/************************************************************************/
/*                           FlushCache()                               */
/************************************************************************/

CPLErr VRTSimpleSource::FlushCache()

{
    if( m_poMaskBandMainBand != nullptr )
    {
        return m_poMaskBandMainBand->FlushCache();
    }
    else if( m_poRasterBand != nullptr )
    {
        return m_poRasterBand->FlushCache();
    }
    return CE_None;
}

/************************************************************************/
/*                    UnsetPreservedRelativeFilenames()                 */
/************************************************************************/

void VRTSimpleSource::UnsetPreservedRelativeFilenames()
{
    m_bRelativeToVRTOri = -1;
    m_osSourceFileNameOri = "";
}

/************************************************************************/
/*                             SetSrcBand()                             */
/************************************************************************/

void VRTSimpleSource::SetSrcBand( GDALRasterBand *poNewSrcBand )

{
    m_poRasterBand = poNewSrcBand;
}

/************************************************************************/
/*                          SetSrcMaskBand()                            */
/************************************************************************/

// poSrcBand is not the mask band, but the band from which the mask band is
// taken.
void VRTSimpleSource::SetSrcMaskBand( GDALRasterBand *poNewSrcBand )

{
    m_poRasterBand = poNewSrcBand->GetMaskBand();
    m_poMaskBandMainBand = poNewSrcBand;
}

/************************************************************************/
/*                         RoundIfCloseToInt()                          */
/************************************************************************/

static double RoundIfCloseToInt(double dfValue)
{
    double dfClosestInt = floor(dfValue + 0.5);
    return (fabs( dfValue - dfClosestInt ) < 1e-5) ? dfClosestInt : dfValue;
}

/************************************************************************/
/*                            SetSrcWindow()                            */
/************************************************************************/

void VRTSimpleSource::SetSrcWindow( double dfNewXOff, double dfNewYOff,
                                    double dfNewXSize, double dfNewYSize )

{
    m_dfSrcXOff = RoundIfCloseToInt(dfNewXOff);
    m_dfSrcYOff = RoundIfCloseToInt(dfNewYOff);
    m_dfSrcXSize = RoundIfCloseToInt(dfNewXSize);
    m_dfSrcYSize = RoundIfCloseToInt(dfNewYSize);
}

/************************************************************************/
/*                            SetDstWindow()                            */
/************************************************************************/

void VRTSimpleSource::SetDstWindow( double dfNewXOff, double dfNewYOff,
                                    double dfNewXSize, double dfNewYSize )

{
    m_dfDstXOff = RoundIfCloseToInt(dfNewXOff);
    m_dfDstYOff = RoundIfCloseToInt(dfNewYOff);
    m_dfDstXSize = RoundIfCloseToInt(dfNewXSize);
    m_dfDstYSize = RoundIfCloseToInt(dfNewYSize);
}

/************************************************************************/
/*                           SetNoDataValue()                           */
/************************************************************************/

void VRTSimpleSource::SetNoDataValue( double dfNewNoDataValue )

{
    if( dfNewNoDataValue == VRT_NODATA_UNSET )
    {
        m_bNoDataSet = FALSE;
        m_dfNoDataValue = VRT_NODATA_UNSET;
        return;
    }

    m_bNoDataSet = TRUE;
    m_dfNoDataValue = dfNewNoDataValue;
}

/************************************************************************/
/*                           SerializeToXML()                           */
/************************************************************************/

static const char* const apszSpecialSyntax[] = {
    "HDF5:\"{FILENAME}\":{ANY}",
    "HDF5:{FILENAME}:{ANY}",
    "NETCDF:\"{FILENAME}\":{ANY}",
    "NETCDF:{FILENAME}:{ANY}",
    "NITF_IM:{ANY}:{FILENAME}",
    "PDF:{ANY}:{FILENAME}",
    "RASTERLITE:{FILENAME},{ANY}",
    "TILEDB:\"{FILENAME}\":{ANY}",
    "TILEDB:{FILENAME}:{ANY}"
 };

CPLXMLNode *VRTSimpleSource::SerializeToXML( const char *pszVRTPath )

{
    if( m_poRasterBand == nullptr )
        return nullptr;

    GDALDataset *poDS = nullptr;

    if( m_poMaskBandMainBand )
    {
        poDS = m_poMaskBandMainBand->GetDataset();
        if( poDS == nullptr || m_poMaskBandMainBand->GetBand() < 1 )
            return nullptr;
    }
    else
    {
        poDS = m_poRasterBand->GetDataset();
        if( poDS == nullptr || m_poRasterBand->GetBand() < 1 )
            return nullptr;
    }

    CPLXMLNode * const psSrc =
        CPLCreateXMLNode( nullptr, CXT_Element, "SimpleSource" );

    if( !m_osResampling.empty() )
    {
        CPLCreateXMLNode(
            CPLCreateXMLNode( psSrc, CXT_Attribute, "resampling" ),
                CXT_Text, m_osResampling.c_str() );
    }

    VSIStatBufL sStat;
    CPLString osTmp;
    int bRelativeToVRT = FALSE;  // TODO(schwehr): Make this a bool?
    const char *pszRelativePath = nullptr;

    if( m_bRelativeToVRTOri >= 0 )
    {
        pszRelativePath = m_osSourceFileNameOri;
        bRelativeToVRT = m_bRelativeToVRTOri;
    }
    else if( strstr(poDS->GetDescription(), "/vsicurl/http") != nullptr ||
             strstr(poDS->GetDescription(), "/vsicurl/ftp") != nullptr )
    {
        // Testing the existence of remote resources can be excruciating
        // slow, so let's just suppose they exist.
        pszRelativePath = poDS->GetDescription();
        bRelativeToVRT = FALSE;
    }
    // If this isn't actually a file, don't even try to know if it is a
    // relative path. It can't be !, and unfortunately CPLIsFilenameRelative()
    // can only work with strings that are filenames To be clear
    // NITF_TOC_ENTRY:CADRG_JOG-A_250K_1_0:some_path isn't a relative file
    // path.
    else if( VSIStatExL( poDS->GetDescription(), &sStat,
                         VSI_STAT_EXISTS_FLAG ) != 0 )
    {
        pszRelativePath = poDS->GetDescription();
        bRelativeToVRT = FALSE;
        for( size_t i = 0;
             i < sizeof(apszSpecialSyntax) / sizeof(apszSpecialSyntax[0]);
             ++i )
        {
            const char* const pszSyntax = apszSpecialSyntax[i];
            CPLString osPrefix(pszSyntax);
            osPrefix.resize(strchr(pszSyntax, ':') - pszSyntax + 1);
            if( pszSyntax[osPrefix.size()] == '"' )
                osPrefix += '"';
            if( EQUALN(pszRelativePath, osPrefix, osPrefix.size()) )
            {
                if( STARTS_WITH_CI(pszSyntax + osPrefix.size(), "{ANY}") )
                {
                    const char* pszLastPart = strrchr(pszRelativePath, ':') + 1;
                    // CSV:z:/foo.xyz
                    if( (pszLastPart[0] == '/' || pszLastPart[0] == '\\') &&
                        pszLastPart - pszRelativePath >= 3 &&
                        pszLastPart[-3] == ':' )
                        pszLastPart -= 2;
                    CPLString osPrefixFilename(pszRelativePath);
                    osPrefixFilename.resize(pszLastPart - pszRelativePath);
                    pszRelativePath =
                        CPLExtractRelativePath( pszVRTPath, pszLastPart,
                                                &bRelativeToVRT );
                    osTmp = osPrefixFilename + pszRelativePath;
                    pszRelativePath = osTmp.c_str();
                }
                else if( STARTS_WITH_CI(pszSyntax + osPrefix.size(),
                                        "{FILENAME}") )
                {
                    CPLString osFilename(pszRelativePath + osPrefix.size());
                    size_t nPos = 0;
                    if( osFilename.size() >= 3 && osFilename[1] == ':' &&
                        (osFilename[2] == '\\' || osFilename[2] == '/') )
                        nPos = 2;
                    nPos =
                        osFilename.find(
                            pszSyntax[osPrefix.size() + strlen("{FILENAME}")],
                            nPos );
                    if( nPos != std::string::npos )
                    {
                        const CPLString osSuffix = osFilename.substr(nPos);
                        osFilename.resize(nPos);
                        pszRelativePath =
                            CPLExtractRelativePath( pszVRTPath, osFilename,
                                        &bRelativeToVRT );
                        osTmp = osPrefix + pszRelativePath + osSuffix;
                        pszRelativePath = osTmp.c_str();
                    }
                }
                break;
            }
        }
    }
    else
    {
        pszRelativePath =
            CPLExtractRelativePath( pszVRTPath, poDS->GetDescription(),
                                    &bRelativeToVRT );
    }

    CPLSetXMLValue( psSrc, "SourceFilename", pszRelativePath );

    CPLCreateXMLNode(
        CPLCreateXMLNode( CPLGetXMLNode( psSrc, "SourceFilename" ),
                          CXT_Attribute, "relativeToVRT" ),
        CXT_Text, bRelativeToVRT ? "1" : "0" );

    // Determine if we must write the shared attribute. The config option
    // will override the m_nExplicitSharedStatus value
    const char* pszShared = CPLGetConfigOption("VRT_SHARED_SOURCE", nullptr);
    if( (pszShared == nullptr && m_nExplicitSharedStatus == 0) ||
        (pszShared != nullptr && !CPLTestBool(pszShared)) )
    {
        CPLCreateXMLNode(
            CPLCreateXMLNode( CPLGetXMLNode( psSrc, "SourceFilename" ),
                              CXT_Attribute, "shared" ),
                              CXT_Text, "0" );
    }

    char** papszOpenOptions = poDS->GetOpenOptions();
    GDALSerializeOpenOptionsToXML(psSrc, papszOpenOptions);

    if( m_poMaskBandMainBand )
        CPLSetXMLValue( psSrc, "SourceBand",
                        CPLSPrintf("mask,%d",m_poMaskBandMainBand->GetBand()) );
    else
        CPLSetXMLValue( psSrc, "SourceBand",
                        CPLSPrintf("%d",m_poRasterBand->GetBand()) );

    /* Write a few additional useful properties of the dataset */
    /* so that we can use a proxy dataset when re-opening. See XMLInit() */
    /* below */
    CPLSetXMLValue( psSrc, "SourceProperties.#RasterXSize",
                    CPLSPrintf("%d",m_poRasterBand->GetXSize()) );
    CPLSetXMLValue( psSrc, "SourceProperties.#RasterYSize",
                    CPLSPrintf("%d",m_poRasterBand->GetYSize()) );
    CPLSetXMLValue( psSrc, "SourceProperties.#DataType",
                GDALGetDataTypeName( m_poRasterBand->GetRasterDataType() ) );

    int nBlockXSize = 0;
    int nBlockYSize = 0;
    m_poRasterBand->GetBlockSize(&nBlockXSize, &nBlockYSize);

    CPLSetXMLValue( psSrc, "SourceProperties.#BlockXSize",
                    CPLSPrintf("%d",nBlockXSize) );
    CPLSetXMLValue( psSrc, "SourceProperties.#BlockYSize",
                    CPLSPrintf("%d",nBlockYSize) );

    if( m_dfSrcXOff != -1
        || m_dfSrcYOff != -1
        || m_dfSrcXSize != -1
        || m_dfSrcYSize != -1 )
    {
        CPLSetXMLValue( psSrc, "SrcRect.#xOff",
                        CPLSPrintf( "%.15g", m_dfSrcXOff ) );
        CPLSetXMLValue( psSrc, "SrcRect.#yOff",
                        CPLSPrintf( "%.15g", m_dfSrcYOff ) );
        CPLSetXMLValue( psSrc, "SrcRect.#xSize",
                        CPLSPrintf( "%.15g", m_dfSrcXSize ) );
        CPLSetXMLValue( psSrc, "SrcRect.#ySize",
                        CPLSPrintf( "%.15g", m_dfSrcYSize ) );
    }

    if( m_dfDstXOff != -1
        || m_dfDstYOff != -1
        || m_dfDstXSize != -1
        || m_dfDstYSize != -1 )
    {
        CPLSetXMLValue( psSrc, "DstRect.#xOff", CPLSPrintf( "%.15g", m_dfDstXOff ) );
        CPLSetXMLValue( psSrc, "DstRect.#yOff", CPLSPrintf( "%.15g", m_dfDstYOff ) );
        CPLSetXMLValue( psSrc, "DstRect.#xSize",CPLSPrintf( "%.15g", m_dfDstXSize ));
        CPLSetXMLValue( psSrc, "DstRect.#ySize",CPLSPrintf( "%.15g", m_dfDstYSize ));
    }

    return psSrc;
}

/************************************************************************/
/*                              XMLInit()                               */
/************************************************************************/

CPLErr VRTSimpleSource::XMLInit( CPLXMLNode *psSrc, const char *pszVRTPath,
                                 void* pUniqueHandle,
                                 std::map<CPLString, GDALDataset*>& oMapSharedSources )

{
    m_osResampling = CPLGetXMLValue( psSrc, "resampling", "");

/* -------------------------------------------------------------------- */
/*      Prepare filename.                                               */
/* -------------------------------------------------------------------- */
    CPLXMLNode* psSourceFileNameNode = CPLGetXMLNode(psSrc,"SourceFilename");
    const char *pszFilename =
        psSourceFileNameNode ?
        CPLGetXMLValue(psSourceFileNameNode, nullptr, nullptr) : nullptr;

    if( pszFilename == nullptr )
    {
        CPLError( CE_Warning, CPLE_AppDefined,
                  "Missing <SourceFilename> element in VRTRasterBand." );
        return CE_Failure;
    }

    // Backup original filename and relativeToVRT so as to be able to
    // serialize them identically again (#5985)
    m_osSourceFileNameOri = pszFilename;
    m_bRelativeToVRTOri =
        atoi( CPLGetXMLValue( psSourceFileNameNode, "relativetoVRT", "0") );
    const char* pszShared = CPLGetXMLValue( psSourceFileNameNode,
                                            "shared", nullptr );
    if( pszShared == nullptr )
    {
        pszShared = CPLGetConfigOption("VRT_SHARED_SOURCE", nullptr );
    }
    bool bShared = false;
    if( pszShared != nullptr )
    {
        bShared = CPLTestBool(pszShared);
        m_nExplicitSharedStatus = bShared;
    }
    else
    {
        bShared = true;
    }

    CPLString osSrcDSName;
    if( pszVRTPath != nullptr && m_bRelativeToVRTOri )
    {
        bool bDone = false;
        for( size_t i = 0;
             i < sizeof(apszSpecialSyntax) / sizeof(apszSpecialSyntax[0]);
             ++i )
        {
            const char* pszSyntax = apszSpecialSyntax[i];
            CPLString osPrefix(pszSyntax);
            osPrefix.resize(strchr(pszSyntax, ':') - pszSyntax + 1);
            if( pszSyntax[osPrefix.size()] == '"' )
                osPrefix += '"';
            if( EQUALN(pszFilename, osPrefix, osPrefix.size()) )
            {
                if( STARTS_WITH_CI(pszSyntax + osPrefix.size(), "{ANY}") )
                {
                    const char * pszLastPart = strrchr(pszFilename, ':') + 1;
                    // CSV:z:/foo.xyz
                    if( ( pszLastPart[0] == '/' ||
                          pszLastPart[0] == '\\') &&
                        pszLastPart - pszFilename >= 3 &&
                        pszLastPart[-3] == ':' )
                    {
                        pszLastPart -= 2;
                    }
                    CPLString osPrefixFilename = pszFilename;
                    osPrefixFilename.resize(pszLastPart - pszFilename);
                    osSrcDSName = osPrefixFilename +
                        CPLProjectRelativeFilename( pszVRTPath, pszLastPart );
                    bDone = true;
                }
                else if( STARTS_WITH_CI(pszSyntax + osPrefix.size(), "{FILENAME}") )
                {
                    CPLString osFilename(pszFilename + osPrefix.size());
                    size_t nPos = 0;
                    if( osFilename.size() >= 3 && osFilename[1] == ':' &&
                        (osFilename[2] == '\\' || osFilename[2] == '/') )
                        nPos = 2;
                    nPos = osFilename.find(
                        pszSyntax[osPrefix.size() + strlen("{FILENAME}")],
                        nPos);
                    if( nPos != std::string::npos )
                    {
                        const CPLString osSuffix = osFilename.substr(nPos);
                        osFilename.resize(nPos);
                        osSrcDSName =
                            osPrefix + CPLProjectRelativeFilename(
                                pszVRTPath, osFilename ) + osSuffix;
                        bDone = true;
                    }
                }
                break;
            }
        }
        if( !bDone )
        {
            osSrcDSName = CPLProjectRelativeFilename( pszVRTPath, pszFilename );
        }
    }
    else
    {
        osSrcDSName = pszFilename;
    }

    const char* pszSourceBand = CPLGetXMLValue(psSrc,"SourceBand","1");
    int nSrcBand = 0;
    bool bGetMaskBand = false;
    if( STARTS_WITH_CI(pszSourceBand, "mask") )
    {
        bGetMaskBand = true;
        if( pszSourceBand[4] == ',' )
            nSrcBand = atoi(pszSourceBand + 5);
        else
            nSrcBand = 1;
    }
    else
    {
        nSrcBand = atoi(pszSourceBand);
    }
    if( !GDALCheckBandCount(nSrcBand, 0) )
    {
        CPLError( CE_Warning, CPLE_AppDefined,
                  "Invalid <SourceBand> element in VRTRasterBand." );
        return CE_Failure;
    }

    // Newly generated VRT will have RasterXSize, RasterYSize, DataType,
    // BlockXSize, BlockYSize tags, so that we don't have actually to
    // open the real dataset immediately, but we can use a proxy dataset
    // instead. This is particularly useful when dealing with huge VRT
    // For example, a VRT with the world coverage of DTED0 (25594 files).
    CPLXMLNode* psSrcProperties = CPLGetXMLNode(psSrc,"SourceProperties");
    int nRasterXSize = 0;
    int nRasterYSize = 0;
    // TODO(schwehr): What is the difference between 0 (GDT_Unknown) and -1?
    // Does there need to be a GDT_Uninitialized?
    GDALDataType eDataType = static_cast<GDALDataType>(-1);
    int nBlockXSize = 0;
    int nBlockYSize = 0;
    if( psSrcProperties )
    {
        nRasterXSize =
            atoi(CPLGetXMLValue(psSrcProperties, "RasterXSize", "0"));
        nRasterYSize =
            atoi(CPLGetXMLValue(psSrcProperties, "RasterYSize", "0"));
        const char *pszDataType =
            CPLGetXMLValue(psSrcProperties, "DataType", nullptr);
        if( pszDataType != nullptr )
        {
            for( int iType = 0; iType < GDT_TypeCount; iType++ )
            {
                const char *pszThisName =
                    GDALGetDataTypeName(static_cast<GDALDataType>(iType));

                if( pszThisName != nullptr && EQUAL(pszDataType, pszThisName) )
                {
                    eDataType = static_cast<GDALDataType>(iType);
                    break;
                }
            }
        }
        nBlockXSize = atoi(CPLGetXMLValue(psSrcProperties, "BlockXSize", "0"));
        nBlockYSize = atoi(CPLGetXMLValue(psSrcProperties, "BlockYSize", "0"));
        if( nRasterXSize < 0 || nRasterYSize < 0 ||
            nBlockXSize < 0 || nBlockYSize < 0 )
        {
            CPLError( CE_Warning, CPLE_AppDefined,
                      "Invalid <SourceProperties> element in VRTRasterBand." );
            return CE_Failure;
        }
    }

    char** papszOpenOptions = GDALDeserializeOpenOptionsFromXML(psSrc);
    if( strstr(osSrcDSName.c_str(),"<VRTDataset") != nullptr )
        papszOpenOptions =
            CSLSetNameValue(papszOpenOptions, "ROOT_PATH", pszVRTPath);

    bool bAddToMapIfOk = false;
    GDALDataset *poSrcDS = nullptr;
    if( nRasterXSize == 0 || nRasterYSize == 0 ||
        eDataType == static_cast<GDALDataType>(-1) ||
        nBlockXSize == 0 || nBlockYSize == 0 )
    {
        /* ----------------------------------------------------------------- */
        /*      Open the file (shared).                                      */
        /* ----------------------------------------------------------------- */
        const int nOpenFlags = GDAL_OF_RASTER | GDAL_OF_VERBOSE_ERROR;
        if( bShared )
        {
            // We no longer use GDAL_OF_SHARED as this can cause quite
            // annoying reference cycles in situations like you have
            // foo.tif and foo.tif.ovr, the later being actually a VRT file
            // that points to foo.tif
            auto oIter = oMapSharedSources.find(osSrcDSName);
            if( oIter != oMapSharedSources.end() )
            {
                poSrcDS = oIter->second;
                poSrcDS->Reference();
            }
            else
            {
                poSrcDS = static_cast<GDALDataset *>( GDALOpenEx(
                        osSrcDSName, nOpenFlags, nullptr,
                        (const char* const* )papszOpenOptions, nullptr ) );
                if( poSrcDS )
                {
                    bAddToMapIfOk = true;
                }
            }
        }
        else
        {
            poSrcDS = static_cast<GDALDataset *>( GDALOpenEx(
                        osSrcDSName, nOpenFlags, nullptr,
                        (const char* const* )papszOpenOptions, nullptr ) );
        }
    }
    else
    {
        /* ----------------------------------------------------------------- */
        /*      Create a proxy dataset                                       */
        /* ----------------------------------------------------------------- */
        CPLString osUniqueHandle( CPLSPrintf("%p", pUniqueHandle) );
        GDALProxyPoolDataset * const proxyDS =
            new GDALProxyPoolDataset( osSrcDSName, nRasterXSize, nRasterYSize,
                                      GA_ReadOnly, bShared, nullptr, nullptr,
                                      osUniqueHandle.c_str() );
        proxyDS->SetOpenOptions(papszOpenOptions);
        poSrcDS = proxyDS;

        // Only the information of rasterBand nSrcBand will be accurate
        // but that's OK since we only use that band afterwards.
        //
        // Previously this added a src band for every band <= nSrcBand, but this becomes
        // prohibitely expensive for files with a large number of bands. This optimization
        // only adds the desired band and the rest of the bands will simply be initialized with a nullptr.
        // This assumes no other code here accesses any of the lower bands in the GDALProxyPoolDataset.
        // It has been suggested that in addition, we should to try share GDALProxyPoolDataset between multiple
        // Simple Sources, which would save on memory for papoBands. For now, that's not implemented.
        proxyDS->AddSrcBand(nSrcBand, eDataType, nBlockXSize, nBlockYSize);

        if( bGetMaskBand )
        {
          GDALProxyPoolRasterBand *poMaskBand =
              dynamic_cast<GDALProxyPoolRasterBand *>(
              proxyDS->GetRasterBand(nSrcBand) );
          if( poMaskBand == nullptr )
          {
              CPLError(
                  CE_Fatal, CPLE_AssertionFailed, "dynamic_cast failed." );
          }
          else
          {
              poMaskBand->AddSrcMaskBandDescription(
                  eDataType, nBlockXSize, nBlockYSize );
          }
        }
    }

    CSLDestroy(papszOpenOptions);

    if( poSrcDS == nullptr )
        return CE_Failure;

/* -------------------------------------------------------------------- */
/*      Get the raster band.                                            */
/* -------------------------------------------------------------------- */

    m_poRasterBand = poSrcDS->GetRasterBand(nSrcBand);
    if( m_poRasterBand == nullptr )
    {
        poSrcDS->ReleaseRef();
        return CE_Failure;
    }
    else if( bAddToMapIfOk )
    {
        oMapSharedSources[osSrcDSName] = poSrcDS;
    }

    if( bGetMaskBand )
    {
        m_poMaskBandMainBand = m_poRasterBand;
        m_poRasterBand = m_poRasterBand->GetMaskBand();
        if( m_poRasterBand == nullptr )
            return CE_Failure;
    }

/* -------------------------------------------------------------------- */
/*      Set characteristics.                                            */
/* -------------------------------------------------------------------- */
    CPLXMLNode * const psSrcRect = CPLGetXMLNode(psSrc,"SrcRect");
    if( psSrcRect )
    {
        double xOff = CPLAtof(CPLGetXMLValue(psSrcRect,"xOff","-1"));
        double yOff = CPLAtof(CPLGetXMLValue(psSrcRect,"yOff","-1"));
        double xSize = CPLAtof(CPLGetXMLValue(psSrcRect,"xSize","-1"));
        double ySize = CPLAtof(CPLGetXMLValue(psSrcRect,"ySize","-1"));
        if( !CPLIsFinite(xOff) || !CPLIsFinite(yOff) ||
            !CPLIsFinite(xSize) || !CPLIsFinite(ySize) ||
            xOff < INT_MIN || xOff > INT_MAX ||
            yOff < INT_MIN || yOff > INT_MAX ||
            !(xSize > 0 || xSize == -1) || xSize > INT_MAX ||
            !(ySize > 0 || ySize == -1) || ySize > INT_MAX )
        {
            CPLError(CE_Failure, CPLE_AppDefined, "Wrong values in SrcRect");
            return CE_Failure;
        }
        SetSrcWindow( xOff, yOff, xSize, ySize );
    }
    else
    {
        m_dfSrcXOff = -1;
        m_dfSrcYOff = -1;
        m_dfSrcXSize = -1;
        m_dfSrcYSize = -1;
    }

    CPLXMLNode * const psDstRect = CPLGetXMLNode(psSrc,"DstRect");
    if( psDstRect )
    {
        double xOff = CPLAtof(CPLGetXMLValue(psDstRect,"xOff","-1"));
        double yOff = CPLAtof(CPLGetXMLValue(psDstRect,"yOff","-1"));
        double xSize = CPLAtof(CPLGetXMLValue(psDstRect,"xSize","-1"));
        double ySize = CPLAtof(CPLGetXMLValue(psDstRect,"ySize","-1"));
        if( !CPLIsFinite(xOff) || !CPLIsFinite(yOff) ||
            !CPLIsFinite(xSize) || !CPLIsFinite(ySize) ||
            xOff < INT_MIN || xOff > INT_MAX ||
            yOff < INT_MIN || yOff > INT_MAX ||
            !(xSize > 0 || xSize == -1) || xSize > INT_MAX ||
            !(ySize > 0 || ySize == -1) || ySize > INT_MAX )
        {
            CPLError(CE_Failure, CPLE_AppDefined, "Wrong values in DstRect");
            return CE_Failure;
        }
        SetDstWindow( xOff, yOff, xSize, ySize );
    }
    else
    {
      m_dfDstXOff = -1;
      m_dfDstYOff = -1;
      m_dfDstXSize = -1;
      m_dfDstYSize = -1;
    }

    return CE_None;
}

/************************************************************************/
/*                             GetFileList()                            */
/************************************************************************/

void VRTSimpleSource::GetFileList( char*** ppapszFileList, int *pnSize,
                                   int *pnMaxSize, CPLHashSet* hSetFiles )
{
    const char* pszFilename = nullptr;
    if( m_poRasterBand != nullptr && m_poRasterBand->GetDataset() != nullptr &&
        (pszFilename = m_poRasterBand->GetDataset()->GetDescription()) != nullptr )
    {
/* -------------------------------------------------------------------- */
/*      Is the filename even a real filesystem object?                  */
/* -------------------------------------------------------------------- */
        if( strstr(pszFilename, "/vsicurl/http") != nullptr ||
            strstr(pszFilename, "/vsicurl/ftp") != nullptr )
        {
            // Testing the existence of remote resources can be excruciating
            // slow, so just suppose they exist.
        }
        else
        {
            VSIStatBufL  sStat;
            if( VSIStatExL( pszFilename, &sStat, VSI_STAT_EXISTS_FLAG ) != 0 )
                return;
        }

/* -------------------------------------------------------------------- */
/*      Is it already in the list ?                                     */
/* -------------------------------------------------------------------- */
        if( CPLHashSetLookup(hSetFiles, pszFilename) != nullptr )
            return;

/* -------------------------------------------------------------------- */
/*      Grow array if necessary                                         */
/* -------------------------------------------------------------------- */
        if( *pnSize + 1 >= *pnMaxSize )
        {
            *pnMaxSize = std::max(*pnSize + 2, 2 + 2 * (*pnMaxSize));
            *ppapszFileList = static_cast<char **>( CPLRealloc(
                *ppapszFileList, sizeof(char*) * (*pnMaxSize) ) );
        }

/* -------------------------------------------------------------------- */
/*      Add the string to the list                                      */
/* -------------------------------------------------------------------- */
        (*ppapszFileList)[*pnSize] = CPLStrdup(pszFilename);
        (*ppapszFileList)[(*pnSize + 1)] = nullptr;
        CPLHashSetInsert(hSetFiles, (*ppapszFileList)[*pnSize]);

        (*pnSize) ++;
    }
}

/************************************************************************/
/*                             GetBand()                                */
/************************************************************************/

GDALRasterBand* VRTSimpleSource::GetBand()
{
    return m_poMaskBandMainBand ? nullptr : m_poRasterBand;
}

/************************************************************************/
/*                       IsSameExceptBandNumber()                       */
/************************************************************************/

int VRTSimpleSource::IsSameExceptBandNumber( VRTSimpleSource* poOtherSource )
{
    return m_dfSrcXOff == poOtherSource->m_dfSrcXOff &&
           m_dfSrcYOff == poOtherSource->m_dfSrcYOff &&
           m_dfSrcXSize == poOtherSource->m_dfSrcXSize &&
           m_dfSrcYSize == poOtherSource->m_dfSrcYSize &&
           m_dfDstXOff == poOtherSource->m_dfDstXOff &&
           m_dfDstYOff == poOtherSource->m_dfDstYOff &&
           m_dfDstXSize == poOtherSource->m_dfDstXSize &&
           m_dfDstYSize == poOtherSource->m_dfDstYSize &&
           m_bNoDataSet == poOtherSource->m_bNoDataSet &&
           m_dfNoDataValue == poOtherSource->m_dfNoDataValue &&
           GetBand() != nullptr && poOtherSource->GetBand() != nullptr &&
           GetBand()->GetDataset() != nullptr &&
           poOtherSource->GetBand()->GetDataset() != nullptr &&
           EQUAL(GetBand()->GetDataset()->GetDescription(),
                 poOtherSource->GetBand()->GetDataset()->GetDescription());
}

/************************************************************************/
/*                              SrcToDst()                              */
/*                                                                      */
/*      Note: this is a no-op if the dst window is -1,-1,-1,-1.         */
/************************************************************************/

void VRTSimpleSource::SrcToDst( double dfX, double dfY,
                                double &dfXOut, double &dfYOut ) const

{
    dfXOut = ((dfX - m_dfSrcXOff) / m_dfSrcXSize) * m_dfDstXSize + m_dfDstXOff;
    dfYOut = ((dfY - m_dfSrcYOff) / m_dfSrcYSize) * m_dfDstYSize + m_dfDstYOff;
}

/************************************************************************/
/*                              DstToSrc()                              */
/*                                                                      */
/*      Note: this is a no-op if the dst window is -1,-1,-1,-1.         */
/************************************************************************/

void VRTSimpleSource::DstToSrc( double dfX, double dfY,
                                double &dfXOut, double &dfYOut ) const

{
    dfXOut = ((dfX - m_dfDstXOff) / m_dfDstXSize) * m_dfSrcXSize + m_dfSrcXOff;
    dfYOut = ((dfY - m_dfDstYOff) / m_dfDstYSize) * m_dfSrcYSize + m_dfSrcYOff;
}

/************************************************************************/
/*                          GetSrcDstWindow()                           */
/************************************************************************/

int
VRTSimpleSource::GetSrcDstWindow( int nXOff, int nYOff, int nXSize, int nYSize,
                                  int nBufXSize, int nBufYSize,
                                  double *pdfReqXOff, double *pdfReqYOff,
                                  double *pdfReqXSize, double *pdfReqYSize,
                                  int *pnReqXOff, int *pnReqYOff,
                                  int *pnReqXSize, int *pnReqYSize,
                                  int *pnOutXOff, int *pnOutYOff,
                                  int *pnOutXSize, int *pnOutYSize )

{
    if( m_dfSrcXSize == 0.0 || m_dfSrcYSize == 0.0 ||
        m_dfDstXSize == 0.0 || m_dfDstYSize == 0.0 )
    {
        return FALSE;
    }

    const bool bDstWinSet = m_dfDstXOff != -1 || m_dfDstXSize != -1
        || m_dfDstYOff != -1 || m_dfDstYSize != -1;

#ifdef DEBUG
    const bool bSrcWinSet = m_dfSrcXOff != -1 || m_dfSrcXSize != -1
        || m_dfSrcYOff != -1 || m_dfSrcYSize != -1;

    if( bSrcWinSet != bDstWinSet )
    {
        return FALSE;
    }
#endif

/* -------------------------------------------------------------------- */
/*      If the input window completely misses the portion of the        */
/*      virtual dataset provided by this source we have nothing to do.  */
/* -------------------------------------------------------------------- */
    if( bDstWinSet )
    {
        if( nXOff >= m_dfDstXOff + m_dfDstXSize
            || nYOff >= m_dfDstYOff + m_dfDstYSize
            || nXOff + nXSize < m_dfDstXOff
            || nYOff + nYSize < m_dfDstYOff )
            return FALSE;
    }

/* -------------------------------------------------------------------- */
/*      This request window corresponds to the whole output buffer.     */
/* -------------------------------------------------------------------- */
    *pnOutXOff = 0;
    *pnOutYOff = 0;
    *pnOutXSize = nBufXSize;
    *pnOutYSize = nBufYSize;

/* -------------------------------------------------------------------- */
/*      If the input window extents outside the portion of the on       */
/*      the virtual file that this source can set, then clip down       */
/*      the requested window.                                           */
/* -------------------------------------------------------------------- */
    bool bModifiedX = false;
    bool bModifiedY = false;
    double dfRXOff = nXOff;
    double dfRYOff = nYOff;
    double dfRXSize = nXSize;
    double dfRYSize = nYSize;

    if( bDstWinSet )
    {
        if( dfRXOff < m_dfDstXOff )
        {
            dfRXSize = dfRXSize + dfRXOff - m_dfDstXOff;
            dfRXOff = m_dfDstXOff;
            bModifiedX = true;
        }

        if( dfRYOff < m_dfDstYOff )
        {
            dfRYSize = dfRYSize + dfRYOff - m_dfDstYOff;
            dfRYOff = m_dfDstYOff;
            bModifiedY = true;
        }

        if( dfRXOff + dfRXSize > m_dfDstXOff + m_dfDstXSize )
        {
            dfRXSize = m_dfDstXOff + m_dfDstXSize - dfRXOff;
            bModifiedX = true;
        }

        if( dfRYOff + dfRYSize > m_dfDstYOff + m_dfDstYSize )
        {
            dfRYSize = m_dfDstYOff + m_dfDstYSize - dfRYOff;
            bModifiedY = true;
        }
    }

/* -------------------------------------------------------------------- */
/*      Translate requested region in virtual file into the source      */
/*      band coordinates.                                               */
/* -------------------------------------------------------------------- */
    const double dfScaleX = m_dfSrcXSize / m_dfDstXSize;
    const double dfScaleY = m_dfSrcYSize / m_dfDstYSize;

    *pdfReqXOff = (dfRXOff - m_dfDstXOff) * dfScaleX + m_dfSrcXOff;
    *pdfReqYOff = (dfRYOff - m_dfDstYOff) * dfScaleY + m_dfSrcYOff;
    *pdfReqXSize = dfRXSize * dfScaleX;
    *pdfReqYSize = dfRYSize * dfScaleY;

    if( !CPLIsFinite(*pdfReqXOff) ||
        !CPLIsFinite(*pdfReqYOff) ||
        !CPLIsFinite(*pdfReqXSize) ||
        !CPLIsFinite(*pdfReqYSize) ||
        *pdfReqXOff > INT_MAX ||
        *pdfReqYOff > INT_MAX ||
        *pdfReqXSize < 0 ||
        *pdfReqYSize < 0 )
    {
        return FALSE;
    }

/* -------------------------------------------------------------------- */
/*      Clamp within the bounds of the available source data.           */
/* -------------------------------------------------------------------- */
    if( *pdfReqXOff < 0 )
    {
        *pdfReqXSize += *pdfReqXOff;
        *pdfReqXOff = 0;
        bModifiedX = true;
    }
    if( *pdfReqYOff < 0 )
    {
        *pdfReqYSize += *pdfReqYOff;
        *pdfReqYOff = 0;
        bModifiedY = true;
    }

    *pnReqXOff = static_cast<int>( floor(*pdfReqXOff) );
    *pnReqYOff = static_cast<int>( floor(*pdfReqYOff) );

    if( *pdfReqXSize > INT_MAX )
        *pnReqXSize = INT_MAX;
    else
        *pnReqXSize = static_cast<int>( floor(*pdfReqXSize + 0.5) );

    if( *pdfReqYSize > INT_MAX )
        *pnReqYSize = INT_MAX;
    else
        *pnReqYSize = static_cast<int>( floor(*pdfReqYSize + 0.5) );

/* -------------------------------------------------------------------- */
/*      Clamp within the bounds of the available source data.           */
/* -------------------------------------------------------------------- */

    if( *pnReqXSize == 0 )
        *pnReqXSize = 1;
    if( *pnReqYSize == 0 )
        *pnReqYSize = 1;

    if( *pnReqXSize > INT_MAX - *pnReqXOff ||
        *pnReqXOff + *pnReqXSize > m_poRasterBand->GetXSize() )
    {
        *pnReqXSize = m_poRasterBand->GetXSize() - *pnReqXOff;
        bModifiedX = true;
    }
    if( *pdfReqXOff + *pdfReqXSize > m_poRasterBand->GetXSize() )
    {
        *pdfReqXSize = m_poRasterBand->GetXSize() - *pdfReqXOff;
        bModifiedX = true;
    }

    if( *pnReqYSize > INT_MAX - *pnReqYOff ||
        *pnReqYOff + *pnReqYSize > m_poRasterBand->GetYSize() )
    {
        *pnReqYSize = m_poRasterBand->GetYSize() - *pnReqYOff;
        bModifiedY = true;
    }
    if( *pdfReqYOff + *pdfReqYSize > m_poRasterBand->GetYSize() )
    {
        *pdfReqYSize = m_poRasterBand->GetYSize() - *pdfReqYOff;
        bModifiedY = true;
    }

/* -------------------------------------------------------------------- */
/*      Don't do anything if the requesting region is completely off    */
/*      the source image.                                               */
/* -------------------------------------------------------------------- */
    if( *pnReqXOff >= m_poRasterBand->GetXSize()
        || *pnReqYOff >= m_poRasterBand->GetYSize()
        || *pnReqXSize <= 0 || *pnReqYSize <= 0 )
    {
        return FALSE;
    }

/* -------------------------------------------------------------------- */
/*      If we haven't had to modify the source rectangle, then the      */
/*      destination rectangle must be the whole region.                 */
/* -------------------------------------------------------------------- */
    if( !bModifiedX && !bModifiedY )
        return TRUE;

/* -------------------------------------------------------------------- */
/*      Now transform this possibly reduced request back into the       */
/*      destination buffer coordinates in case the output region is     */
/*      less than the whole buffer.                                     */
/* -------------------------------------------------------------------- */
    double dfDstULX = 0.0;
    double dfDstULY = 0.0;
    double dfDstLRX = 0.0;
    double dfDstLRY = 0.0;

    SrcToDst( *pdfReqXOff, *pdfReqYOff, dfDstULX, dfDstULY );
    SrcToDst( *pdfReqXOff + *pdfReqXSize, *pdfReqYOff + *pdfReqYSize,
              dfDstLRX, dfDstLRY );
#if DEBUG_VERBOSE
    CPLDebug( "VRT", "dfDstULX=%g dfDstULY=%g dfDstLRX=%g dfDstLRY=%g",
              dfDstULX, dfDstULY, dfDstLRX, dfDstLRY );
#endif

    if( bModifiedX )
    {
        const double dfScaleWinToBufX =
            nBufXSize / static_cast<double>( nXSize );

        const double dfOutXOff = (dfDstULX - nXOff) * dfScaleWinToBufX;
        if( dfOutXOff <= 0 )
            *pnOutXOff = 0;
        else if( dfOutXOff > INT_MAX )
            *pnOutXOff = INT_MAX;
        else
            *pnOutXOff = (int) (dfOutXOff+0.001);

        // Apply correction on floating-point source window
        {
            double dfDstDeltaX = (dfOutXOff - *pnOutXOff) / dfScaleWinToBufX;
            double dfSrcDeltaX = dfDstDeltaX / m_dfDstXSize * m_dfSrcXSize;
            *pdfReqXOff -= dfSrcDeltaX;
            *pdfReqXSize = std::min( *pdfReqXSize + dfSrcDeltaX,
                                     static_cast<double>(INT_MAX) );
        }

        double dfOutRightXOff = (dfDstLRX - nXOff) * dfScaleWinToBufX;
        if( dfOutRightXOff < dfOutXOff )
            return FALSE;
        if( dfOutRightXOff > INT_MAX )
            dfOutRightXOff = INT_MAX;
        *pnOutXSize = (int) ceil(dfOutRightXOff-0.001) - *pnOutXOff;

        if( *pnOutXSize > INT_MAX - *pnOutXOff ||
            *pnOutXOff + *pnOutXSize > nBufXSize )
            *pnOutXSize = nBufXSize - *pnOutXOff;

        // Apply correction on floating-point source window
        {
            double dfDstDeltaX = (ceil(dfOutRightXOff) - dfOutRightXOff) / dfScaleWinToBufX;
            double dfSrcDeltaX = dfDstDeltaX / m_dfDstXSize * m_dfSrcXSize;
            *pdfReqXSize = std::min( *pdfReqXSize + dfSrcDeltaX,
                                     static_cast<double>(INT_MAX) );
        }
    }

    if( bModifiedY )
    {
        const double dfScaleWinToBufY =
            nBufYSize / static_cast<double>( nYSize );

        const double dfOutYOff = (dfDstULY - nYOff) * dfScaleWinToBufY;
        if( dfOutYOff <= 0 )
            *pnOutYOff = 0;
        else if( dfOutYOff > INT_MAX )
            *pnOutYOff = INT_MAX;
        else
            *pnOutYOff = static_cast<int>(dfOutYOff+0.001);

        // Apply correction on floating-point source window
        {
            double dfDstDeltaY = (dfOutYOff - *pnOutYOff) / dfScaleWinToBufY;
            double dfSrcDeltaY = dfDstDeltaY / m_dfDstYSize * m_dfSrcYSize;
            *pdfReqYOff -= dfSrcDeltaY;
            *pdfReqYSize = std::min( *pdfReqYSize + dfSrcDeltaY,
                                     static_cast<double>(INT_MAX) );
        }

        double dfOutTopYOff = (dfDstLRY - nYOff) * dfScaleWinToBufY;
        if( dfOutTopYOff < dfOutYOff )
            return FALSE;
        if( dfOutTopYOff > INT_MAX )
            dfOutTopYOff = INT_MAX;
        *pnOutYSize = static_cast<int>( ceil(dfOutTopYOff-0.001) ) - *pnOutYOff;

        if( *pnOutYSize > INT_MAX - *pnOutYOff ||
            *pnOutYOff + *pnOutYSize > nBufYSize )
            *pnOutYSize = nBufYSize - *pnOutYOff;

        // Apply correction on floating-point source window
        {
            double dfDstDeltaY = (ceil(dfOutTopYOff) - dfOutTopYOff) / dfScaleWinToBufY;
            double dfSrcDeltaY = dfDstDeltaY / m_dfDstYSize * m_dfSrcYSize;
            *pdfReqYSize = std::min( *pdfReqYSize + dfSrcDeltaY,
                                     static_cast<double>(INT_MAX) );
        }
    }

    if( *pnOutXSize < 1 || *pnOutYSize < 1 )
        return FALSE;

    return TRUE;
}

/************************************************************************/
/*                          NeedMaxValAdjustment()                      */
/************************************************************************/

int VRTSimpleSource::NeedMaxValAdjustment() const
{
    if( !m_nMaxValue )
        return FALSE;

    const char* pszNBITS =
        m_poRasterBand->GetMetadataItem("NBITS", "IMAGE_STRUCTURE");
    const int nBits = (pszNBITS) ? atoi(pszNBITS) : 0;
    if( nBits >= 1 && nBits <= 31 )
    {
        const int nBandMaxValue = static_cast<int>((1U << nBits) - 1);
        return nBandMaxValue > m_nMaxValue;
    }
    return TRUE;
}

/************************************************************************/
/*                              RasterIO()                              */
/************************************************************************/

CPLErr
VRTSimpleSource::RasterIO( GDALDataType eBandDataType,
                           int nXOff, int nYOff, int nXSize, int nYSize,
                           void *pData, int nBufXSize, int nBufYSize,
                           GDALDataType eBufType,
                           GSpacing nPixelSpace,
                           GSpacing nLineSpace,
                           GDALRasterIOExtraArg* psExtraArgIn )

{
    GDALRasterIOExtraArg sExtraArg;
    INIT_RASTERIO_EXTRA_ARG(sExtraArg);
    GDALRasterIOExtraArg* psExtraArg = &sExtraArg;

    // The window we will actually request from the source raster band.
    double dfReqXOff = 0.0;
    double dfReqYOff = 0.0;
    double dfReqXSize = 0.0;
    double dfReqYSize = 0.0;
    int nReqXOff = 0;
    int nReqYOff = 0;
    int nReqXSize = 0;
    int nReqYSize = 0;

    // The window we will actual set _within_ the pData buffer.
    int nOutXOff = 0;
    int nOutYOff = 0;
    int nOutXSize = 0;
    int nOutYSize = 0;

    if( !GetSrcDstWindow( nXOff, nYOff, nXSize, nYSize,
                          nBufXSize, nBufYSize,
                          &dfReqXOff, &dfReqYOff, &dfReqXSize, &dfReqYSize,
                          &nReqXOff, &nReqYOff, &nReqXSize, &nReqYSize,
                          &nOutXOff, &nOutYOff, &nOutXSize, &nOutYSize ) )
    {
        return CE_None;
    }
#if DEBUG_VERBOSE
    CPLDebug(
        "VRT",
        "nXOff=%d, nYOff=%d, nXSize=%d, nYSize=%d, nBufXSize=%d, nBufYSize=%d,\n"
        "dfReqXOff=%g, dfReqYOff=%g, dfReqXSize=%g, dfReqYSize=%g,\n"
        "nReqXOff=%d, nReqYOff=%d, nReqXSize=%d, nReqYSize=%d,\n"
        "nOutXOff=%d, nOutYOff=%d, nOutXSize=%d, nOutYSize=%d",
        nXOff, nYOff, nXSize, nYSize,
        nBufXSize, nBufYSize,
        dfReqXOff, dfReqYOff, dfReqXSize, dfReqYSize,
        nReqXOff, nReqYOff, nReqXSize, nReqYSize,
        nOutXOff, nOutYOff, nOutXSize, nOutYSize );
#endif

/* -------------------------------------------------------------------- */
/*      Actually perform the IO request.                                */
/* -------------------------------------------------------------------- */
    if( !m_osResampling.empty() )
    {
        psExtraArg->eResampleAlg = GDALRasterIOGetResampleAlg(m_osResampling);
    }
    else if( psExtraArgIn != nullptr )
    {
        psExtraArg->eResampleAlg = psExtraArgIn->eResampleAlg;
    }
    psExtraArg->bFloatingPointWindowValidity = TRUE;
    psExtraArg->dfXOff = dfReqXOff;
    psExtraArg->dfYOff = dfReqYOff;
    psExtraArg->dfXSize = dfReqXSize;
    psExtraArg->dfYSize = dfReqYSize;

    GByte* pabyOut =
        static_cast<unsigned char *>(pData)
        + nOutXOff * nPixelSpace
        + static_cast<GPtrDiff_t>(nOutYOff) * nLineSpace;

    CPLErr eErr = CE_Failure;

    if( GDALDataTypeIsConversionLossy(m_poRasterBand->GetRasterDataType(),
                                      eBandDataType) )
    {
        const int nBandDTSize = GDALGetDataTypeSizeBytes(eBandDataType);
        void* pTemp = VSI_MALLOC3_VERBOSE(nOutXSize, nOutYSize, nBandDTSize);
        if( pTemp )
        {
            eErr =
                m_poRasterBand->RasterIO(
                    GF_Read,
                    nReqXOff, nReqYOff, nReqXSize, nReqYSize,
                    pTemp,
                    nOutXSize, nOutYSize,
                    eBandDataType, 0, 0, psExtraArg );
            if( eErr == CE_None )
            {
                GByte* pabyTemp = reinterpret_cast<GByte*>(pTemp);
                for( int iY = 0; iY < nOutYSize; iY++ )
                {
                    GDALCopyWords(pabyTemp + static_cast<size_t>(iY) *
                                                    nBandDTSize * nOutXSize,
                                  eBandDataType, nBandDTSize,
                                  pabyOut +
                                    static_cast<size_t>(iY) * nLineSpace,
                                  eBufType,
                                  static_cast<int>(nPixelSpace),
                                  nOutXSize);
                }
            }
            VSIFree(pTemp);
        }
    }
    else
    {
        eErr =
            m_poRasterBand->RasterIO(
                GF_Read,
                nReqXOff, nReqYOff, nReqXSize, nReqYSize,
                pabyOut,
                nOutXSize, nOutYSize,
                eBufType, nPixelSpace, nLineSpace, psExtraArg );
    }

    if( NeedMaxValAdjustment() )
    {
        for( int j = 0; j < nOutYSize; j++ )
        {
            for( int i = 0; i < nOutXSize; i++ )
            {
                int nVal = 0;
                GDALCopyWords( pabyOut + j * nLineSpace + i * nPixelSpace,
                               eBufType, 0,
                               &nVal, GDT_Int32, 0,
                               1 );
                if( nVal > m_nMaxValue )
                    nVal = m_nMaxValue;
                GDALCopyWords( &nVal, GDT_Int32, 0,
                               pabyOut + j * nLineSpace + i * nPixelSpace,
                               eBufType, 0,
                               1);
            }
        }
    }

    return eErr;
}

/************************************************************************/
/*                             GetMinimum()                             */
/************************************************************************/

double VRTSimpleSource::GetMinimum( int nXSize, int nYSize, int *pbSuccess )
{
    // The window we will actually request from the source raster band.
    double dfReqXOff = 0.0;
    double dfReqYOff = 0.0;
    double dfReqXSize = 0.0;
    double dfReqYSize = 0.0;
    int nReqXOff = 0;
    int nReqYOff = 0;
    int nReqXSize = 0;
    int nReqYSize = 0;

    // The window we will actual set _within_ the pData buffer.
    int nOutXOff = 0;
    int nOutYOff = 0;
    int nOutXSize = 0;
    int nOutYSize = 0;

    if( !GetSrcDstWindow( 0, 0, nXSize, nYSize,
                          nXSize, nYSize,
                          &dfReqXOff, &dfReqYOff, &dfReqXSize, &dfReqYSize,
                          &nReqXOff, &nReqYOff, &nReqXSize, &nReqYSize,
                          &nOutXOff, &nOutYOff, &nOutXSize, &nOutYSize ) ||
        nReqXOff != 0 || nReqYOff != 0 ||
        nReqXSize != m_poRasterBand->GetXSize() ||
        nReqYSize != m_poRasterBand->GetYSize())
    {
        *pbSuccess = FALSE;
        return 0;
    }

    const double dfVal = m_poRasterBand->GetMinimum(pbSuccess);
    if( NeedMaxValAdjustment() && dfVal > m_nMaxValue )
        return m_nMaxValue;
    return dfVal;
}

/************************************************************************/
/*                             GetMaximum()                             */
/************************************************************************/

double VRTSimpleSource::GetMaximum( int nXSize, int nYSize, int *pbSuccess )
{
    // The window we will actually request from the source raster band.
    double dfReqXOff = 0.0;
    double dfReqYOff = 0.0;
    double dfReqXSize = 0.0;
    double dfReqYSize = 0.0;
    int nReqXOff = 0;
    int nReqYOff = 0;
    int nReqXSize = 0;
    int nReqYSize = 0;

    // The window we will actual set _within_ the pData buffer.
    int nOutXOff = 0;
    int nOutYOff = 0;
    int nOutXSize = 0;
    int nOutYSize = 0;

    if( !GetSrcDstWindow( 0, 0, nXSize, nYSize,
                          nXSize, nYSize,
                          &dfReqXOff, &dfReqYOff, &dfReqXSize, &dfReqYSize,
                          &nReqXOff, &nReqYOff, &nReqXSize, &nReqYSize,
                          &nOutXOff, &nOutYOff, &nOutXSize, &nOutYSize ) ||
        nReqXOff != 0 || nReqYOff != 0 ||
        nReqXSize != m_poRasterBand->GetXSize() ||
        nReqYSize != m_poRasterBand->GetYSize())
    {
        *pbSuccess = FALSE;
        return 0;
    }

    const double dfVal = m_poRasterBand->GetMaximum(pbSuccess);
    if( NeedMaxValAdjustment() && dfVal > m_nMaxValue )
        return m_nMaxValue;
    return dfVal;
}

/************************************************************************/
/*                       ComputeRasterMinMax()                          */
/************************************************************************/

CPLErr VRTSimpleSource::ComputeRasterMinMax( int nXSize, int nYSize,
                                             int bApproxOK, double* adfMinMax )
{
    // The window we will actually request from the source raster band.
    double dfReqXOff = 0.0;
    double dfReqYOff = 0.0;
    double dfReqXSize = 0.0;
    double dfReqYSize = 0.0;
    int nReqXOff = 0;
    int nReqYOff = 0;
    int nReqXSize = 0;
    int nReqYSize = 0;

    // The window we will actual set _within_ the pData buffer.
    int nOutXOff = 0;
    int nOutYOff = 0;
    int nOutXSize = 0;
    int nOutYSize = 0;

    if( !GetSrcDstWindow( 0, 0, nXSize, nYSize,
                          nXSize, nYSize,
                          &dfReqXOff, &dfReqYOff, &dfReqXSize, &dfReqYSize,
                          &nReqXOff, &nReqYOff, &nReqXSize, &nReqYSize,
                          &nOutXOff, &nOutYOff, &nOutXSize, &nOutYSize ) ||
        nReqXOff != 0 || nReqYOff != 0 ||
        nReqXSize != m_poRasterBand->GetXSize() ||
        nReqYSize != m_poRasterBand->GetYSize())
    {
        return CE_Failure;
    }

    const CPLErr eErr =
        m_poRasterBand->ComputeRasterMinMax( bApproxOK, adfMinMax );
    if( NeedMaxValAdjustment() )
    {
        if( adfMinMax[0] > m_nMaxValue )
            adfMinMax[0] = m_nMaxValue;
        if( adfMinMax[1] > m_nMaxValue )
            adfMinMax[1] = m_nMaxValue;
    }
    return eErr;
}

/************************************************************************/
/*                         ComputeStatistics()                          */
/************************************************************************/

CPLErr VRTSimpleSource::ComputeStatistics(
    int nXSize, int nYSize,
    int bApproxOK,
    double *pdfMin, double *pdfMax,
    double *pdfMean, double *pdfStdDev,
    GDALProgressFunc pfnProgress, void *pProgressData )
{
    // The window we will actually request from the source raster band.
    double dfReqXOff = 0.0;
    double dfReqYOff = 0.0;
    double dfReqXSize = 0.0;
    double dfReqYSize = 0.0;
    int nReqXOff = 0;
    int nReqYOff = 0;
    int nReqXSize = 0;
    int nReqYSize = 0;

    // The window we will actual set _within_ the pData buffer.
    int nOutXOff = 0;
    int nOutYOff = 0;
    int nOutXSize = 0;
    int nOutYSize = 0;

    if( NeedMaxValAdjustment() ||
        !GetSrcDstWindow( 0, 0, nXSize, nYSize,
                          nXSize, nYSize,
                          &dfReqXOff, &dfReqYOff, &dfReqXSize, &dfReqYSize,
                          &nReqXOff, &nReqYOff, &nReqXSize, &nReqYSize,
                          &nOutXOff, &nOutYOff, &nOutXSize, &nOutYSize ) ||
        nReqXOff != 0 || nReqYOff != 0 ||
        nReqXSize != m_poRasterBand->GetXSize() ||
        nReqYSize != m_poRasterBand->GetYSize())
    {
        return CE_Failure;
    }

    return m_poRasterBand->ComputeStatistics( bApproxOK, pdfMin, pdfMax,
                                              pdfMean, pdfStdDev,
                                              pfnProgress, pProgressData );
}

/************************************************************************/
/*                            GetHistogram()                            */
/************************************************************************/

CPLErr VRTSimpleSource::GetHistogram(
    int nXSize, int nYSize,
    double dfMin, double dfMax,
    int nBuckets, GUIntBig * panHistogram,
    int bIncludeOutOfRange, int bApproxOK,
    GDALProgressFunc pfnProgress, void *pProgressData )
{
    // The window we will actually request from the source raster band.
    double dfReqXOff = 0.0;
    double dfReqYOff = 0.0;
    double dfReqXSize = 0.0;
    double dfReqYSize = 0.0;
    int nReqXOff = 0;
    int nReqYOff = 0;
    int nReqXSize = 0;
    int nReqYSize = 0;

    // The window we will actual set _within_ the pData buffer.
    int nOutXOff = 0;
    int nOutYOff = 0;
    int nOutXSize = 0;
    int nOutYSize = 0;

    if( NeedMaxValAdjustment() ||
        !GetSrcDstWindow( 0, 0, nXSize, nYSize,
                          nXSize, nYSize,
                          &dfReqXOff, &dfReqYOff, &dfReqXSize, &dfReqYSize,
                          &nReqXOff, &nReqYOff, &nReqXSize, &nReqYSize,
                          &nOutXOff, &nOutYOff, &nOutXSize, &nOutYSize ) ||
        nReqXOff != 0 || nReqYOff != 0 ||
        nReqXSize != m_poRasterBand->GetXSize() ||
        nReqYSize != m_poRasterBand->GetYSize())
    {
        return CE_Failure;
    }

    return m_poRasterBand->GetHistogram( dfMin, dfMax, nBuckets,
                                         panHistogram,
                                         bIncludeOutOfRange, bApproxOK,
                                         pfnProgress, pProgressData );
}

/************************************************************************/
/*                          DatasetRasterIO()                           */
/************************************************************************/

CPLErr VRTSimpleSource::DatasetRasterIO(
    GDALDataType eBandDataType,
    int nXOff, int nYOff, int nXSize, int nYSize,
    void * pData, int nBufXSize, int nBufYSize,
    GDALDataType eBufType,
    int nBandCount, int *panBandMap,
    GSpacing nPixelSpace, GSpacing nLineSpace,
    GSpacing nBandSpace,
    GDALRasterIOExtraArg* psExtraArgIn )
{
    if( !EQUAL(GetType(), "SimpleSource") )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "DatasetRasterIO() not implemented for %s", GetType());
        return CE_Failure;
    }

    GDALRasterIOExtraArg sExtraArg;
    INIT_RASTERIO_EXTRA_ARG(sExtraArg);
    GDALRasterIOExtraArg* psExtraArg = &sExtraArg;

    // The window we will actually request from the source raster band.
    double dfReqXOff = 0.0;
    double dfReqYOff = 0.0;
    double dfReqXSize = 0.0;
    double dfReqYSize = 0.0;
    int nReqXOff = 0;
    int nReqYOff = 0;
    int nReqXSize = 0;
    int nReqYSize = 0;

    // The window we will actual set _within_ the pData buffer.
    int nOutXOff = 0;
    int nOutYOff = 0;
    int nOutXSize = 0;
    int nOutYSize = 0;

    if( !GetSrcDstWindow( nXOff, nYOff, nXSize, nYSize,
                          nBufXSize, nBufYSize,
                          &dfReqXOff, &dfReqYOff, &dfReqXSize, &dfReqYSize,
                          &nReqXOff, &nReqYOff, &nReqXSize, &nReqYSize,
                          &nOutXOff, &nOutYOff, &nOutXSize, &nOutYSize ) )
    {
        return CE_None;
    }

    GDALDataset* poDS = m_poRasterBand->GetDataset();
    if( poDS == nullptr )
        return CE_Failure;

    if( !m_osResampling.empty() )
    {
        psExtraArg->eResampleAlg = GDALRasterIOGetResampleAlg(m_osResampling);
    }
    else if( psExtraArgIn != nullptr )
    {
        psExtraArg->eResampleAlg = psExtraArgIn->eResampleAlg;
    }
    psExtraArg->bFloatingPointWindowValidity = TRUE;
    psExtraArg->dfXOff = dfReqXOff;
    psExtraArg->dfYOff = dfReqYOff;
    psExtraArg->dfXSize = dfReqXSize;
    psExtraArg->dfYSize = dfReqYSize;

    GByte* pabyOut =
        static_cast<unsigned char *>(pData)
        + nOutXOff * nPixelSpace
        + (GPtrDiff_t)nOutYOff * nLineSpace;

    CPLErr eErr = CE_Failure;

    if( GDALDataTypeIsConversionLossy(m_poRasterBand->GetRasterDataType(),
                                      eBandDataType) )
    {
        const int nBandDTSize = GDALGetDataTypeSizeBytes(eBandDataType);
        void* pTemp = VSI_MALLOC3_VERBOSE(nOutXSize, nOutYSize,
                                          nBandDTSize * nBandCount);
        if( pTemp )
        {
            eErr = poDS->RasterIO(
                GF_Read,
                nReqXOff, nReqYOff, nReqXSize, nReqYSize,
                pTemp,
                nOutXSize, nOutYSize,
                eBandDataType, nBandCount, panBandMap,
                0, 0, 0, psExtraArg );
            if( eErr == CE_None )
            {
                GByte* pabyTemp = reinterpret_cast<GByte*>(pTemp);
                const size_t nSrcBandSpace = static_cast<size_t>(nOutYSize) *
                                                nOutXSize * nBandDTSize;
                for( int iBand = 0; iBand < nBandCount; iBand ++ )
                {
                    for( int iY = 0; iY < nOutYSize; iY++ )
                    {
                        GDALCopyWords(pabyTemp + iBand * nSrcBandSpace +
                                        static_cast<size_t>(iY) * nBandDTSize * nOutXSize,
                                    eBandDataType, nBandDTSize,
                                    pabyOut +
                                        static_cast<size_t>(iY) * nLineSpace +
                                        static_cast<size_t>(iBand) * nBandSpace,
                                    eBufType, static_cast<int>(nPixelSpace),
                                    nOutXSize);
                    }
                }
            }
            VSIFree(pTemp);
        }
    }
    else
    {
        eErr = poDS->RasterIO(
            GF_Read,
            nReqXOff, nReqYOff, nReqXSize, nReqYSize,
            pabyOut,
            nOutXSize, nOutYSize,
            eBufType, nBandCount, panBandMap,
            nPixelSpace, nLineSpace, nBandSpace, psExtraArg );
    }

    if( NeedMaxValAdjustment() )
    {
        for( int k = 0; k < nBandCount; k++ )
        {
            for( int j = 0; j < nOutYSize; j++ )
            {
                for( int i = 0; i < nOutXSize; i++ )
                {
                    int nVal = 0;
                    GDALCopyWords(
                        pabyOut + k * nBandSpace + j * nLineSpace +
                            i * nPixelSpace,
                        eBufType, 0,
                        &nVal, GDT_Int32, 0,
                        1 );

                    if( nVal > m_nMaxValue )
                        nVal = m_nMaxValue;

                    GDALCopyWords(
                        &nVal, GDT_Int32, 0,
                        pabyOut + k * nBandSpace + j * nLineSpace +
                            i * nPixelSpace,
                        eBufType, 0,
                        1 );
                }
            }
        }
    }

    return eErr;
}

/************************************************************************/
/*                          SetResampling()                             */
/************************************************************************/

void VRTSimpleSource::SetResampling( const char* pszResampling )
{
    m_osResampling = (pszResampling) ? pszResampling : "";
}

/************************************************************************/
/* ==================================================================== */
/*                         VRTAveragedSource                            */
/* ==================================================================== */
/************************************************************************/

/************************************************************************/
/*                         VRTAveragedSource()                          */
/************************************************************************/

VRTAveragedSource::VRTAveragedSource() {}

/************************************************************************/
/*                           SerializeToXML()                           */
/************************************************************************/

CPLXMLNode *VRTAveragedSource::SerializeToXML( const char *pszVRTPath )

{
    CPLXMLNode * const psSrc = VRTSimpleSource::SerializeToXML( pszVRTPath );

    if( psSrc == nullptr )
        return nullptr;

    CPLFree( psSrc->pszValue );
    psSrc->pszValue = CPLStrdup( "AveragedSource" );

    return psSrc;
}

/************************************************************************/
/*                              RasterIO()                              */
/************************************************************************/

CPLErr
VRTAveragedSource::RasterIO( GDALDataType /*eBandDataType*/,
                             int nXOff, int nYOff, int nXSize, int nYSize,
                             void *pData, int nBufXSize, int nBufYSize,
                             GDALDataType eBufType,
                             GSpacing nPixelSpace,
                             GSpacing nLineSpace,
                             GDALRasterIOExtraArg* psExtraArgIn )

{
    GDALRasterIOExtraArg sExtraArg;
    INIT_RASTERIO_EXTRA_ARG(sExtraArg);
    GDALRasterIOExtraArg* psExtraArg = &sExtraArg;

    // The window we will actually request from the source raster band.
    double dfReqXOff = 0.0;
    double dfReqYOff = 0.0;
    double dfReqXSize = 0.0;
    double dfReqYSize = 0.0;
    int nReqXOff = 0;
    int nReqYOff = 0;
    int nReqXSize = 0;
    int nReqYSize = 0;

    // The window we will actual set _within_ the pData buffer.
    int nOutXOff = 0;
    int nOutYOff = 0;
    int nOutXSize = 0;
    int nOutYSize = 0;

    if( !GetSrcDstWindow( nXOff, nYOff, nXSize, nYSize, nBufXSize, nBufYSize,
                          &dfReqXOff, &dfReqYOff, &dfReqXSize, &dfReqYSize,
                          &nReqXOff, &nReqYOff, &nReqXSize, &nReqYSize,
                          &nOutXOff, &nOutYOff, &nOutXSize, &nOutYSize ) )
        return CE_None;

/* -------------------------------------------------------------------- */
/*      Allocate a temporary buffer to whole the full resolution        */
/*      data from the area of interest.                                 */
/* -------------------------------------------------------------------- */
    float * const pafSrc = static_cast<float *>(
        VSI_MALLOC3_VERBOSE(sizeof(float), nReqXSize, nReqYSize) );
    if( pafSrc == nullptr )
    {
        return CE_Failure;
    }

/* -------------------------------------------------------------------- */
/*      Load it.                                                        */
/* -------------------------------------------------------------------- */
    if( !m_osResampling.empty() )
    {
        psExtraArg->eResampleAlg = GDALRasterIOGetResampleAlg(m_osResampling);
    }
    else if( psExtraArgIn != nullptr )
    {
        psExtraArg->eResampleAlg = psExtraArgIn->eResampleAlg;
    }

    psExtraArg->bFloatingPointWindowValidity = TRUE;
    psExtraArg->dfXOff = dfReqXOff;
    psExtraArg->dfYOff = dfReqYOff;
    psExtraArg->dfXSize = dfReqXSize;
    psExtraArg->dfYSize = dfReqYSize;

    const CPLErr eErr =
        m_poRasterBand->RasterIO( GF_Read,
                                  nReqXOff, nReqYOff, nReqXSize, nReqYSize,
                                  pafSrc, nReqXSize, nReqYSize, GDT_Float32,
                                  0, 0, psExtraArg );

    if( eErr != CE_None )
    {
        VSIFree( pafSrc );
        return eErr;
    }

/* -------------------------------------------------------------------- */
/*      Do the averaging.                                               */
/* -------------------------------------------------------------------- */
    for( int iBufLine = nOutYOff; iBufLine < nOutYOff + nOutYSize; iBufLine++ )
    {
        const double dfYDst =
            (iBufLine / static_cast<double>(nBufYSize) ) * nYSize + nYOff;

        for( int iBufPixel = nOutXOff;
             iBufPixel < nOutXOff + nOutXSize;
             iBufPixel++ )
        {
            double dfXSrcStart, dfXSrcEnd, dfYSrcStart, dfYSrcEnd;
            int    iXSrcStart, iYSrcStart, iXSrcEnd, iYSrcEnd;

            const double dfXDst =
                (iBufPixel / static_cast<double>(nBufXSize)) * nXSize + nXOff;

            // Compute the source image rectangle needed for this pixel.
            DstToSrc( dfXDst, dfYDst, dfXSrcStart, dfYSrcStart );
            DstToSrc( dfXDst+1.0, dfYDst+1.0, dfXSrcEnd, dfYSrcEnd );

            // Convert to integers, assuming that the center of the source
            // pixel must be in our rect to get included.
            if( dfXSrcEnd >= dfXSrcStart + 1 )
            {
                iXSrcStart = static_cast<int>(floor(dfXSrcStart+0.5));
                iXSrcEnd = static_cast<int>(floor(dfXSrcEnd+0.5));
            }
            else
            {
                /* If the resampling factor is less than 100%, the distance */
                /* between the source pixel is < 1, so we stick to nearest */
                /* neighbour */
                iXSrcStart = static_cast<int>(floor(dfXSrcStart));
                iXSrcEnd = iXSrcStart + 1;
            }
            if( dfYSrcEnd >= dfYSrcStart + 1 )
            {
                iYSrcStart = static_cast<int>(floor(dfYSrcStart+0.5));
                iYSrcEnd = static_cast<int>(floor(dfYSrcEnd+0.5));
            }
            else
            {
                iYSrcStart = static_cast<int>(floor(dfYSrcStart));
                iYSrcEnd = iYSrcStart + 1;
            }

            // Transform into the coordinate system of the source *buffer*
            iXSrcStart -= nReqXOff;
            iYSrcStart -= nReqYOff;
            iXSrcEnd -= nReqXOff;
            iYSrcEnd -= nReqYOff;

            double dfSum = 0.0;
            int nPixelCount = 0;

            for( int iY = iYSrcStart; iY < iYSrcEnd; iY++ )
            {
                if( iY < 0 || iY >= nReqYSize )
                    continue;

                for( int iX = iXSrcStart; iX < iXSrcEnd; iX++ )
                {
                    if( iX < 0 || iX >= nReqXSize )
                        continue;

                    const float fSampledValue = pafSrc[iX + static_cast<size_t>(iY) * nReqXSize];
                    if( CPLIsNan(fSampledValue) )
                        continue;

                    if( m_bNoDataSet &&
                        GDALIsValueInRange<float>(m_dfNoDataValue) &&
                        ARE_REAL_EQUAL(fSampledValue,
                                       static_cast<float>(m_dfNoDataValue)))
                        continue;

                    nPixelCount++;
                    dfSum += pafSrc[iX + static_cast<size_t>(iY) * nReqXSize];
                }
            }

            if( nPixelCount == 0 )
                continue;

            // Compute output value.
            const float dfOutputValue = static_cast<float>(dfSum / nPixelCount);

            // Put it in the output buffer.
            GByte *pDstLocation =
                static_cast<GByte *>(pData)
                + nPixelSpace * iBufPixel
                + static_cast<GPtrDiff_t>(nLineSpace) * iBufLine;

            if( eBufType == GDT_Byte )
                *pDstLocation =
                    static_cast<GByte>(
                        std::min(255.0, std::max(0.0, dfOutputValue + 0.5)) );
            else
                GDALCopyWords( &dfOutputValue, GDT_Float32, 4,
                               pDstLocation, eBufType, 8, 1 );
        }
    }

    VSIFree( pafSrc );

    return CE_None;
}

/************************************************************************/
/*                             GetMinimum()                             */
/************************************************************************/

double VRTAveragedSource::GetMinimum( int /* nXSize */,
                                      int /* nYSize */,
                                      int *pbSuccess )
{
    *pbSuccess = FALSE;
    return 0.0;
}

/************************************************************************/
/*                             GetMaximum()                             */
/************************************************************************/

double VRTAveragedSource::GetMaximum( int /* nXSize */,
                                      int /* nYSize */,
                                      int *pbSuccess )
{
    *pbSuccess = FALSE;
    return 0.0;
}

/************************************************************************/
/*                       ComputeRasterMinMax()                          */
/************************************************************************/

CPLErr VRTAveragedSource::ComputeRasterMinMax( int /* nXSize */,
                                               int /* nYSize */,
                                               int /* bApproxOK */,
                                               double* /* adfMinMax */)
{
    return CE_Failure;
}

/************************************************************************/
/*                         ComputeStatistics()                          */
/************************************************************************/

CPLErr VRTAveragedSource::ComputeStatistics( int /* nXSize */,
                                             int /* nYSize */,
                                             int /* bApproxOK */,
                                             double * /* pdfMin */,
                                             double * /* pdfMax */,
                                             double * /* pdfMean */,
                                             double * /* pdfStdDev */,
                                             GDALProgressFunc /* pfnProgress */,
                                             void * /* pProgressData */ )
{
    return CE_Failure;
}

/************************************************************************/
/*                            GetHistogram()                            */
/************************************************************************/

CPLErr VRTAveragedSource::GetHistogram( int /* nXSize */,
                                        int /* nYSize */,
                                        double /* dfMin */,
                                        double /* dfMax */,
                                        int /* nBuckets */,
                                        GUIntBig * /* panHistogram */,
                                        int /* bIncludeOutOfRange */,
                                        int /* bApproxOK */,
                                        GDALProgressFunc /* pfnProgress */,
                                        void * /* pProgressData */)
{
    return CE_Failure;
}

/************************************************************************/
/* ==================================================================== */
/*                          VRTComplexSource                            */
/* ==================================================================== */
/************************************************************************/

/************************************************************************/
/*                          VRTComplexSource()                          */
/************************************************************************/

VRTComplexSource::VRTComplexSource() :
    m_eScalingType(VRT_SCALING_NONE),
    m_dfScaleOff(0.0),
    m_dfScaleRatio(1.0),
    m_bSrcMinMaxDefined(FALSE),
    m_dfSrcMin(0.0),
    m_dfSrcMax(0.0),
    m_dfDstMin(0.0),
    m_dfDstMax(0.0),
    m_dfExponent(1.0),
    m_nColorTableComponent(0),
    m_padfLUTInputs(nullptr),
    m_padfLUTOutputs(nullptr),
    m_nLUTItemCount(0)
{}

VRTComplexSource::VRTComplexSource( const VRTComplexSource* poSrcSource,
                                    double dfXDstRatio, double dfYDstRatio ) :
    VRTSimpleSource(poSrcSource, dfXDstRatio, dfYDstRatio),
    m_eScalingType(poSrcSource->m_eScalingType),
    m_dfScaleOff(poSrcSource->m_dfScaleOff),
    m_dfScaleRatio(poSrcSource->m_dfScaleRatio),
    m_bSrcMinMaxDefined(poSrcSource->m_bSrcMinMaxDefined),
    m_dfSrcMin(poSrcSource->m_dfSrcMin),
    m_dfSrcMax(poSrcSource->m_dfSrcMax),
    m_dfDstMin(poSrcSource->m_dfDstMin),
    m_dfDstMax(poSrcSource->m_dfDstMax),
    m_dfExponent(poSrcSource->m_dfExponent),
    m_nColorTableComponent(poSrcSource->m_nColorTableComponent),
    m_padfLUTInputs(nullptr),
    m_padfLUTOutputs(nullptr),
    m_nLUTItemCount(poSrcSource->m_nLUTItemCount)
{
    if( m_nLUTItemCount )
    {
        m_padfLUTInputs = static_cast<double *>(
            CPLMalloc(sizeof(double) * m_nLUTItemCount) );
        memcpy( m_padfLUTInputs, poSrcSource->m_padfLUTInputs,
                sizeof(double) * m_nLUTItemCount );

        m_padfLUTOutputs = static_cast<double *>(
            CPLMalloc(sizeof(double) * m_nLUTItemCount) );
        memcpy( m_padfLUTOutputs, poSrcSource->m_padfLUTOutputs,
                sizeof(double) * m_nLUTItemCount);
    }
}

VRTComplexSource::~VRTComplexSource()
{
    VSIFree( m_padfLUTInputs );
    VSIFree( m_padfLUTOutputs );
}

/************************************************************************/
/*                           SerializeToXML()                           */
/************************************************************************/

CPLXMLNode *VRTComplexSource::SerializeToXML( const char *pszVRTPath )

{
    CPLXMLNode *psSrc = VRTSimpleSource::SerializeToXML( pszVRTPath );

    if( psSrc == nullptr )
        return nullptr;

    CPLFree( psSrc->pszValue );
    psSrc->pszValue = CPLStrdup( "ComplexSource" );

    if( m_bNoDataSet )
    {
        if( CPLIsNan(m_dfNoDataValue) )
            CPLSetXMLValue( psSrc, "NODATA", "nan");
        else if( m_poRasterBand->GetRasterDataType() == GDT_Float32 &&
                 m_dfNoDataValue == -std::numeric_limits<float>::max() )
        {
            // To avoid rounding out of the range of float
            CPLSetXMLValue( psSrc, "NODATA", "-3.4028234663852886e+38");
        }
        else if( m_poRasterBand->GetRasterDataType() == GDT_Float32 &&
                 m_dfNoDataValue == std::numeric_limits<float>::max() )
        {
            // To avoid rounding out of the range of float
            CPLSetXMLValue( psSrc, "NODATA", "3.4028234663852886e+38");
        }
        else
        {
            CPLSetXMLValue( psSrc, "NODATA",
                            CPLSPrintf("%.16g", m_dfNoDataValue) );
        }
    }

    switch( m_eScalingType )
    {
        case VRT_SCALING_NONE:
            break;

        case VRT_SCALING_LINEAR:
        {
            CPLSetXMLValue( psSrc, "ScaleOffset",
                            CPLSPrintf("%g", m_dfScaleOff) );
            CPLSetXMLValue( psSrc, "ScaleRatio",
                            CPLSPrintf("%g", m_dfScaleRatio) );
            break;
        }

        case VRT_SCALING_EXPONENTIAL:
        {
            CPLSetXMLValue( psSrc, "Exponent",
                            CPLSPrintf("%g", m_dfExponent) );
            CPLSetXMLValue( psSrc, "SrcMin",
                            CPLSPrintf("%g", m_dfSrcMin) );
            CPLSetXMLValue( psSrc, "SrcMax",
                            CPLSPrintf("%g", m_dfSrcMax) );
            CPLSetXMLValue( psSrc, "DstMin",
                            CPLSPrintf("%g", m_dfDstMin) );
            CPLSetXMLValue( psSrc, "DstMax",
                            CPLSPrintf("%g", m_dfDstMax) );
            break;
        }
    }

    if( m_nLUTItemCount )
    {
        // Make sure we print with sufficient precision to address really close
        // entries (#6422).
        CPLString osLUT;
        // TODO(schwehr): How is this not a read past the end of the array if
        // m_nLUTItemCount is 0 or 1?  Added in
        // https://trac.osgeo.org/gdal/changeset/33779
        if( m_nLUTItemCount > 0 &&
            CPLString().Printf("%g", m_padfLUTInputs[0]) ==
            CPLString().Printf("%g", m_padfLUTInputs[1]) )
        {
            osLUT = CPLString().Printf(
                "%.18g:%g", m_padfLUTInputs[0], m_padfLUTOutputs[0]);
        }
        else
        {
            osLUT = CPLString().Printf(
                "%g:%g", m_padfLUTInputs[0], m_padfLUTOutputs[0]);
        }
        for ( int i = 1; i < m_nLUTItemCount; i++ )
        {
            if( CPLString().Printf("%g", m_padfLUTInputs[i]) ==
                CPLString().Printf("%g", m_padfLUTInputs[i-1]) ||
                (i + 1 < m_nLUTItemCount &&
                 CPLString().Printf("%g", m_padfLUTInputs[i]) ==
                 CPLString().Printf("%g", m_padfLUTInputs[i+1])) )
            {
                // TODO(schwehr): An explanation of the 18 would be helpful.
                // Can someone distill the issue down to a quick comment?
                // https://trac.osgeo.org/gdal/ticket/6422
                osLUT += CPLString().Printf(
                    ",%.18g:%g", m_padfLUTInputs[i], m_padfLUTOutputs[i]);
            }
            else
            {
                osLUT += CPLString().Printf(
                    ",%g:%g", m_padfLUTInputs[i], m_padfLUTOutputs[i]);
            }
        }
        CPLSetXMLValue( psSrc, "LUT", osLUT );
    }

    if( m_nColorTableComponent )
    {
        CPLSetXMLValue( psSrc, "ColorTableComponent",
                        CPLSPrintf("%d", m_nColorTableComponent) );
    }

    return psSrc;
}

/************************************************************************/
/*                              XMLInit()                               */
/************************************************************************/

CPLErr VRTComplexSource::XMLInit( CPLXMLNode *psSrc, const char *pszVRTPath,
                                  void* pUniqueHandle,
                                  std::map<CPLString, GDALDataset*>& oMapSharedSources )

{
/* -------------------------------------------------------------------- */
/*      Do base initialization.                                         */
/* -------------------------------------------------------------------- */
    {
        const CPLErr eErr = VRTSimpleSource::XMLInit( psSrc, pszVRTPath,
                                                      pUniqueHandle,
                                                      oMapSharedSources );
        if( eErr != CE_None )
            return eErr;
    }

/* -------------------------------------------------------------------- */
/*      Complex parameters.                                             */
/* -------------------------------------------------------------------- */
    if( CPLGetXMLValue(psSrc, "ScaleOffset", nullptr) != nullptr
        || CPLGetXMLValue(psSrc, "ScaleRatio", nullptr) != nullptr )
    {
        m_eScalingType = VRT_SCALING_LINEAR;
        m_dfScaleOff = CPLAtof( CPLGetXMLValue(psSrc, "ScaleOffset", "0") );
        m_dfScaleRatio = CPLAtof( CPLGetXMLValue(psSrc, "ScaleRatio", "1") );
    }
    else if( CPLGetXMLValue(psSrc, "Exponent", nullptr) != nullptr &&
             CPLGetXMLValue(psSrc, "DstMin", nullptr) != nullptr &&
             CPLGetXMLValue(psSrc, "DstMax", nullptr) != nullptr )
    {
        m_eScalingType = VRT_SCALING_EXPONENTIAL;
        m_dfExponent = CPLAtof( CPLGetXMLValue(psSrc, "Exponent", "1.0") );

        if( CPLGetXMLValue(psSrc, "SrcMin", nullptr) != nullptr
         && CPLGetXMLValue(psSrc, "SrcMax", nullptr) != nullptr )
        {
            m_dfSrcMin = CPLAtof( CPLGetXMLValue(psSrc, "SrcMin", "0.0") );
            m_dfSrcMax = CPLAtof( CPLGetXMLValue(psSrc, "SrcMax", "0.0") );
            m_bSrcMinMaxDefined = TRUE;
        }

        m_dfDstMin = CPLAtof( CPLGetXMLValue(psSrc, "DstMin", "0.0") );
        m_dfDstMax = CPLAtof( CPLGetXMLValue(psSrc, "DstMax", "0.0") );
    }

    if( CPLGetXMLValue(psSrc, "NODATA", nullptr) != nullptr )
    {
        m_bNoDataSet = TRUE;
        m_dfNoDataValue = CPLAtofM( CPLGetXMLValue(psSrc, "NODATA", "0") );
        if( m_poRasterBand->GetRasterDataType() == GDT_Float32 )
        {
            m_dfNoDataValue = GDALAdjustNoDataCloseToFloatMax(m_dfNoDataValue);
        }
    }

    if( CPLGetXMLValue(psSrc, "LUT", nullptr) != nullptr )
    {
        char **papszValues =
            CSLTokenizeString2(
                CPLGetXMLValue(psSrc, "LUT", ""), ",:", CSLT_ALLOWEMPTYTOKENS);

        if( m_nLUTItemCount )
        {
            if( m_padfLUTInputs )
            {
                VSIFree( m_padfLUTInputs );
                m_padfLUTInputs = nullptr;
            }
            if( m_padfLUTOutputs )
            {
                VSIFree( m_padfLUTOutputs );
                m_padfLUTOutputs = nullptr;
            }
            m_nLUTItemCount = 0;
        }

        m_nLUTItemCount = CSLCount(papszValues) / 2;

        m_padfLUTInputs = static_cast<double *>(
            VSIMalloc2(m_nLUTItemCount, sizeof(double)) );
        if( !m_padfLUTInputs )
        {
            CSLDestroy(papszValues);
            m_nLUTItemCount = 0;
            return CE_Failure;
        }

        m_padfLUTOutputs = static_cast<double *>(
            VSIMalloc2(m_nLUTItemCount, sizeof(double)) );
        if( !m_padfLUTOutputs )
        {
            CSLDestroy(papszValues);
            VSIFree( m_padfLUTInputs );
            m_padfLUTInputs = nullptr;
            m_nLUTItemCount = 0;
            return CE_Failure;
        }

        for ( int nIndex = 0; nIndex < m_nLUTItemCount; nIndex++ )
        {
            m_padfLUTInputs[nIndex] = CPLAtof( papszValues[nIndex * 2] );
            m_padfLUTOutputs[nIndex] = CPLAtof( papszValues[nIndex * 2 + 1] );

            // Enforce the requirement that the LUT input array is
            // monotonically non-decreasing.
            if( nIndex > 0 &&
                m_padfLUTInputs[nIndex] < m_padfLUTInputs[nIndex - 1] )
            {
                CSLDestroy(papszValues);
                VSIFree( m_padfLUTInputs );
                VSIFree( m_padfLUTOutputs );
                m_padfLUTInputs = nullptr;
                m_padfLUTOutputs = nullptr;
                m_nLUTItemCount = 0;
                return CE_Failure;
            }
        }

        CSLDestroy(papszValues);
    }

    if( CPLGetXMLValue(psSrc, "ColorTableComponent", nullptr) != nullptr )
    {
        m_nColorTableComponent =
            atoi( CPLGetXMLValue(psSrc, "ColorTableComponent", "0") );
    }

    return CE_None;
}

/************************************************************************/
/*                              LookupValue()                           */
/************************************************************************/

double
VRTComplexSource::LookupValue( double dfInput )
{
    // Find the index of the first element in the LUT input array that
    // is not smaller than the input value.
    int i = static_cast<int>(
        std::lower_bound( m_padfLUTInputs,
                          m_padfLUTInputs + m_nLUTItemCount,
                          dfInput)
        - m_padfLUTInputs );

    if( i == 0 )
        return m_padfLUTOutputs[0];

    // If the index is beyond the end of the LUT input array, the input
    // value is larger than all the values in the array.
    if( i == m_nLUTItemCount )
        return m_padfLUTOutputs[m_nLUTItemCount - 1];

    if( m_padfLUTInputs[i] == dfInput )
        return m_padfLUTOutputs[i];

    // Otherwise, interpolate.
    return
        m_padfLUTOutputs[i - 1] + (dfInput - m_padfLUTInputs[i - 1]) *
        ( (m_padfLUTOutputs[i] - m_padfLUTOutputs[i - 1]) /
          (m_padfLUTInputs[i] - m_padfLUTInputs[i - 1]) );
}

/************************************************************************/
/*                         SetLinearScaling()                           */
/************************************************************************/

void VRTComplexSource::SetLinearScaling( double dfOffset, double dfScale )
{
    m_eScalingType = VRT_SCALING_LINEAR;
    m_dfScaleOff = dfOffset;
    m_dfScaleRatio = dfScale;
}

/************************************************************************/
/*                         SetPowerScaling()                           */
/************************************************************************/

void VRTComplexSource::SetPowerScaling( double dfExponentIn,
                                        double dfSrcMinIn,
                                        double dfSrcMaxIn,
                                        double dfDstMinIn,
                                        double dfDstMaxIn)
{
    m_eScalingType = VRT_SCALING_EXPONENTIAL;
    m_dfExponent = dfExponentIn;
    m_dfSrcMin = dfSrcMinIn;
    m_dfSrcMax = dfSrcMaxIn;
    m_dfDstMin = dfDstMinIn;
    m_dfDstMax = dfDstMaxIn;
    m_bSrcMinMaxDefined = TRUE;
}

/************************************************************************/
/*                    SetColorTableComponent()                          */
/************************************************************************/

void VRTComplexSource::SetColorTableComponent( int nComponent )
{
    m_nColorTableComponent = nComponent;
}

/************************************************************************/
/*                              RasterIO()                              */
/************************************************************************/

CPLErr
VRTComplexSource::RasterIO( GDALDataType /*eBandDataType*/,
                            int nXOff, int nYOff, int nXSize, int nYSize,
                            void *pData, int nBufXSize, int nBufYSize,
                            GDALDataType eBufType,
                            GSpacing nPixelSpace,
                            GSpacing nLineSpace,
                            GDALRasterIOExtraArg* psExtraArgIn )

{
    GDALRasterIOExtraArg sExtraArg;
    INIT_RASTERIO_EXTRA_ARG(sExtraArg);
    GDALRasterIOExtraArg* psExtraArg = &sExtraArg;

    // The window we will actually request from the source raster band.
    double dfReqXOff = 0.0;
    double dfReqYOff = 0.0;
    double dfReqXSize = 0.0;
    double dfReqYSize = 0.0;
    int nReqXOff = 0;
    int nReqYOff = 0;
    int nReqXSize = 0;
    int nReqYSize = 0;

    // The window we will actual set _within_ the pData buffer.
    int nOutXOff = 0;
    int nOutYOff = 0;
    int nOutXSize = 0;
    int nOutYSize = 0;

    if( !GetSrcDstWindow( nXOff, nYOff, nXSize, nYSize, nBufXSize, nBufYSize,
                          &dfReqXOff, &dfReqYOff, &dfReqXSize, &dfReqYSize,
                          &nReqXOff, &nReqYOff, &nReqXSize, &nReqYSize,
                          &nOutXOff, &nOutYOff, &nOutXSize, &nOutYSize ) )
        return CE_None;
#if DEBUG_VERBOSE
    CPLDebug(
        "VRT",
        "nXOff=%d, nYOff=%d, nXSize=%d, nYSize=%d, nBufXSize=%d, nBufYSize=%d,\n"
        "dfReqXOff=%g, dfReqYOff=%g, dfReqXSize=%g, dfReqYSize=%g,\n"
        "nReqXOff=%d, nReqYOff=%d, nReqXSize=%d, nReqYSize=%d,\n"
        "nOutXOff=%d, nOutYOff=%d, nOutXSize=%d, nOutYSize=%d",
        nXOff, nYOff, nXSize, nYSize,
        nBufXSize, nBufYSize,
        dfReqXOff, dfReqYOff, dfReqXSize, dfReqYSize,
        nReqXOff, nReqYOff, nReqXSize, nReqYSize,
        nOutXOff, nOutYOff, nOutXSize, nOutYSize );
#endif

    if( !m_osResampling.empty() )
    {
        psExtraArg->eResampleAlg = GDALRasterIOGetResampleAlg(m_osResampling);
    }
    else if( psExtraArgIn != nullptr )
    {
        psExtraArg->eResampleAlg = psExtraArgIn->eResampleAlg;
    }
    psExtraArg->bFloatingPointWindowValidity = TRUE;
    psExtraArg->dfXOff = dfReqXOff;
    psExtraArg->dfYOff = dfReqYOff;
    psExtraArg->dfXSize = dfReqXSize;
    psExtraArg->dfYSize = dfReqYSize;

    const bool bIsComplex = CPL_TO_BOOL( GDALDataTypeIsComplex(eBufType) );
    CPLErr eErr;
    // For Int32, float32 isn't sufficiently precise as working data type
    if( eBufType == GDT_CInt32 || eBufType == GDT_CFloat64 ||
        eBufType == GDT_Int32 || eBufType == GDT_UInt32 ||
        eBufType == GDT_Float64 )
    {
        eErr = RasterIOInternal<double>(
                nReqXOff, nReqYOff, nReqXSize, nReqYSize,
                static_cast<GByte *>(pData) + nPixelSpace * nOutXOff
                    + static_cast<GPtrDiff_t>(nLineSpace) * nOutYOff,
                nOutXSize, nOutYSize,
                eBufType,
                nPixelSpace, nLineSpace, psExtraArg,
                bIsComplex ? GDT_CFloat64 : GDT_Float64);
    }
    else
    {
        eErr = RasterIOInternal<float>(
                nReqXOff, nReqYOff, nReqXSize, nReqYSize,
                static_cast<GByte *>(pData) + nPixelSpace * nOutXOff
                    + static_cast<GPtrDiff_t>(nLineSpace) * nOutYOff,
                nOutXSize, nOutYSize,
                eBufType,
                nPixelSpace, nLineSpace, psExtraArg,
                bIsComplex ? GDT_CFloat32 : GDT_Float32);
    }

    return eErr;
}

/************************************************************************/
/*                          RasterIOInternal()                          */
/************************************************************************/

// nReqXOff, nReqYOff, nReqXSize, nReqYSize are expressed in source band
// referential.
template <class WorkingDT>
CPLErr VRTComplexSource::RasterIOInternal( int nReqXOff, int nReqYOff,
                                           int nReqXSize, int nReqYSize,
                                           void *pData,
                                           int nOutXSize, int nOutYSize,
                                           GDALDataType eBufType,
                                           GSpacing nPixelSpace,
                                           GSpacing nLineSpace,
                                           GDALRasterIOExtraArg* psExtraArg,
                                           GDALDataType eWrkDataType )
{
/* -------------------------------------------------------------------- */
/*      Read into a temporary buffer.                                   */
/* -------------------------------------------------------------------- */
    GDALColorTable* poColorTable = nullptr;
    const bool bIsComplex = CPL_TO_BOOL( GDALDataTypeIsComplex(eBufType) );
    const int nWordSize = GDALGetDataTypeSizeBytes(eWrkDataType);
    const bool bNoDataSetIsNan = m_bNoDataSet && CPLIsNan(m_dfNoDataValue);
    const bool bNoDataSetAndNotNan = m_bNoDataSet && !CPLIsNan(m_dfNoDataValue) &&
                                GDALIsValueInRange<WorkingDT>(m_dfNoDataValue);
    const auto fWorkingDataTypeNoData = static_cast<WorkingDT>(m_dfNoDataValue);

    WorkingDT *pafData = nullptr;
    if( m_eScalingType == VRT_SCALING_LINEAR &&
        m_bNoDataSet == FALSE &&
        m_dfScaleRatio == 0 )
    {
/* -------------------------------------------------------------------- */
/*      Optimization when writing a constant value                      */
/*      (used by the -addalpha option of gdalbuildvrt)                  */
/* -------------------------------------------------------------------- */
        // Already set to NULL when defined.
        // pafData = NULL;
    }
    else
    {
        pafData = static_cast<WorkingDT *>(
            VSI_MALLOC3_VERBOSE(nOutXSize,nOutYSize,nWordSize) );
        if( pafData == nullptr )
        {
            return CE_Failure;
        }

        const GDALRIOResampleAlg eResampleAlgBack = psExtraArg->eResampleAlg;
        if( !m_osResampling.empty() )
        {
            psExtraArg->eResampleAlg =
                GDALRasterIOGetResampleAlg(m_osResampling);
        }

        const CPLErr eErr =
            m_poRasterBand->RasterIO( GF_Read,
                                      nReqXOff, nReqYOff,
                                      nReqXSize, nReqYSize,
                                      pafData,
                                      nOutXSize, nOutYSize,
                                      eWrkDataType,
                                      nWordSize,
                                      nWordSize *
                                      static_cast<GSpacing>(nOutXSize),
                                      psExtraArg );
        if( !m_osResampling.empty() )
            psExtraArg->eResampleAlg = eResampleAlgBack;

        if( eErr != CE_None )
        {
            CPLFree( pafData );
            return eErr;
        }

        if( m_nColorTableComponent != 0 )
        {
            poColorTable = m_poRasterBand->GetColorTable();
            if( poColorTable == nullptr )
            {
                CPLError( CE_Failure, CPLE_AppDefined,
                          "Source band has no color table." );
                CPLFree( pafData );
                return CE_Failure;
            }
        }
    }

/* -------------------------------------------------------------------- */
/*      Selectively copy into output buffer with nodata masking,        */
/*      and/or scaling.                                                 */
/* -------------------------------------------------------------------- */
    for( int iY = 0; iY < nOutYSize; iY++ )
    {
        for( int iX = 0; iX < nOutXSize; iX++ )
        {
            GByte *pDstLocation =
                static_cast<GByte *>(pData)
                + nPixelSpace * iX
                + static_cast<GPtrDiff_t>(nLineSpace) * iY;

            if( pafData && !bIsComplex )
            {
                WorkingDT fResult = pafData[iX + iY * nOutXSize];
                if( bNoDataSetIsNan && CPLIsNan(fResult) )
                    continue;
                if( bNoDataSetAndNotNan &&
                    ARE_REAL_EQUAL(fResult, fWorkingDataTypeNoData) )
                    continue;

                if( m_nColorTableComponent )
                {
                    const GDALColorEntry* poEntry =
                        poColorTable->GetColorEntry(static_cast<int>(fResult));
                    if( poEntry )
                    {
                        if( m_nColorTableComponent == 1 )
                            fResult = poEntry->c1;
                        else if( m_nColorTableComponent == 2 )
                            fResult = poEntry->c2;
                        else if( m_nColorTableComponent == 3 )
                            fResult = poEntry->c3;
                        else if( m_nColorTableComponent == 4 )
                            fResult = poEntry->c4;
                    }
                    else
                    {
                        static bool bHasWarned = false;
                        if( !bHasWarned )
                        {
                            bHasWarned = true;
                            CPLError(
                                CE_Failure, CPLE_AppDefined,
                                "No entry %d.", static_cast<int>(fResult) );
                        }
                        continue;
                    }
                }

                if( m_eScalingType == VRT_SCALING_LINEAR )
                {
                    fResult = static_cast<WorkingDT>(
                        fResult * m_dfScaleRatio + m_dfScaleOff );
                }
                else if( m_eScalingType == VRT_SCALING_EXPONENTIAL )
                {
                    if( !m_bSrcMinMaxDefined )
                    {
                        int bSuccessMin = FALSE;
                        int bSuccessMax = FALSE;
                        double adfMinMax[2] = {
                            m_poRasterBand->GetMinimum(&bSuccessMin),
                            m_poRasterBand->GetMaximum(&bSuccessMax) };
                        if( (bSuccessMin && bSuccessMax) ||
                            m_poRasterBand->ComputeRasterMinMax( TRUE,
                                                                 adfMinMax )
                            == CE_None )
                        {
                            m_dfSrcMin = adfMinMax[0];
                            m_dfSrcMax = adfMinMax[1];
                            m_bSrcMinMaxDefined = TRUE;
                        }
                        else
                        {
                            CPLError(
                                CE_Failure, CPLE_AppDefined,
                                "Cannot determine source min/max value" );
                            return CE_Failure;
                        }
                    }

                    double dfPowVal =
                        (fResult - m_dfSrcMin) / (m_dfSrcMax - m_dfSrcMin);
                    if( dfPowVal < 0.0 )
                        dfPowVal = 0.0;
                    else if( dfPowVal > 1.0 )
                        dfPowVal = 1.0;
                    fResult = static_cast<WorkingDT>(
                        (m_dfDstMax - m_dfDstMin) *
                        pow( dfPowVal, m_dfExponent ) +
                        m_dfDstMin);
                }

                if( m_nLUTItemCount )
                    fResult = static_cast<WorkingDT>(LookupValue( fResult ));

                if( m_nMaxValue != 0 && fResult > m_nMaxValue )
                    fResult = static_cast<WorkingDT>(m_nMaxValue);

                if( eBufType == GDT_Byte )
                    *pDstLocation = static_cast<GByte>(
                        std::min(255.0f,
                                 std::max(0.0f,
                                          static_cast<float>(fResult) + 0.5f)));
                else
                    GDALCopyWords( &fResult, eWrkDataType, 0,
                                pDstLocation, eBufType, 0, 1 );
            }
            else if( pafData && bIsComplex )
            {
                WorkingDT afResult[2] = {
                    pafData[2 * (iX + iY * nOutXSize)],
                    pafData[2 * (iX + iY * nOutXSize) + 1] };

                // Do not use color table.
                if( m_eScalingType == VRT_SCALING_LINEAR )
                {
                    afResult[0] = static_cast<WorkingDT>(
                        afResult[0] * m_dfScaleRatio + m_dfScaleOff );
                    afResult[1] = static_cast<WorkingDT>(
                        afResult[1] * m_dfScaleRatio + m_dfScaleOff );
                }

                /* Do not use LUT */

                if( eBufType == GDT_Byte )
                    *pDstLocation = static_cast<GByte>(
                        std::min(255.0, std::max(0.0, afResult[0] + 0.5) ) );
                else
                    GDALCopyWords( afResult, eWrkDataType, 0,
                                   pDstLocation, eBufType, 0, 1 );
            }
            else
            {
                WorkingDT afResult[2] = {
                    static_cast<WorkingDT>(m_dfScaleOff),
                    0 };

                if( m_nLUTItemCount )
                    afResult[0] = static_cast<WorkingDT>(LookupValue( afResult[0] ));

                if( m_nMaxValue != 0 && afResult[0] > m_nMaxValue )
                    afResult[0] = static_cast<WorkingDT>(m_nMaxValue);

                if( eBufType == GDT_Byte )
                    *pDstLocation = static_cast<GByte>(
                        std::min(255.0, std::max(0.0, afResult[0] + 0.5)) );
                else
                    GDALCopyWords( afResult, eWrkDataType, 0,
                                   pDstLocation, eBufType, 0, 1 );
            }
        }
    }

    CPLFree( pafData );

    return CE_None;
}

// Explicitly instantiate template method, as it is used in another file.
template
CPLErr VRTComplexSource::RasterIOInternal<float>( int nReqXOff, int nReqYOff,
                                    int nReqXSize, int nReqYSize,
                                    void *pData, int nOutXSize, int nOutYSize,
                                    GDALDataType eBufType,
                                    GSpacing nPixelSpace, GSpacing nLineSpace,
                                    GDALRasterIOExtraArg* psExtraArg,
                                    GDALDataType eWrkDataType );

/************************************************************************/
/*                        AreValuesUnchanged()                          */
/************************************************************************/

bool VRTComplexSource::AreValuesUnchanged() const
{
    return m_dfScaleOff == 0.0 && m_dfScaleRatio == 1.0 &&
            m_nLUTItemCount == 0 && m_nColorTableComponent == 0 &&
            m_eScalingType != VRT_SCALING_EXPONENTIAL;
}

/************************************************************************/
/*                             GetMinimum()                             */
/************************************************************************/

double VRTComplexSource::GetMinimum( int nXSize, int nYSize, int *pbSuccess )
{
    if( AreValuesUnchanged() )
    {
        return VRTSimpleSource::GetMinimum(nXSize, nYSize, pbSuccess);
    }

    *pbSuccess = FALSE;
    return 0;
}

/************************************************************************/
/*                             GetMaximum()                             */
/************************************************************************/

double VRTComplexSource::GetMaximum( int nXSize, int nYSize, int *pbSuccess )
{
    if( AreValuesUnchanged() )
    {
        return VRTSimpleSource::GetMaximum(nXSize, nYSize, pbSuccess);
    }

    *pbSuccess = FALSE;
    return 0;
}

/************************************************************************/
/*                       ComputeRasterMinMax()                          */
/************************************************************************/

CPLErr VRTComplexSource::ComputeRasterMinMax( int nXSize, int nYSize, int bApproxOK, double* adfMinMax )
{
    if( AreValuesUnchanged() )
    {
        return VRTSimpleSource::ComputeRasterMinMax( nXSize, nYSize, bApproxOK,
                                                     adfMinMax);
    }

    return CE_Failure;
}

/************************************************************************/
/*                            GetHistogram()                            */
/************************************************************************/

CPLErr VRTComplexSource::GetHistogram( int nXSize, int nYSize,
                                       double dfMin, double dfMax,
                                       int nBuckets, GUIntBig * panHistogram,
                                       int bIncludeOutOfRange, int bApproxOK,
                                       GDALProgressFunc pfnProgress,
                                       void *pProgressData )
{
    if( AreValuesUnchanged() )
    {
        return VRTSimpleSource::GetHistogram( nXSize, nYSize,
                                              dfMin, dfMax, nBuckets,
                                              panHistogram,
                                              bIncludeOutOfRange, bApproxOK,
                                              pfnProgress, pProgressData );
    }

    return CE_Failure;
}

/************************************************************************/
/*                         ComputeStatistics()                          */
/************************************************************************/

CPLErr VRTComplexSource::ComputeStatistics( int nXSize, int nYSize,
                                            int bApproxOK,
                                            double *pdfMin, double *pdfMax,
                                            double *pdfMean, double *pdfStdDev,
                                            GDALProgressFunc pfnProgress,
                                            void *pProgressData )
{
    if( AreValuesUnchanged() )
    {
        return VRTSimpleSource::ComputeStatistics( nXSize, nYSize, bApproxOK,
                                                   pdfMin, pdfMax,
                                                   pdfMean, pdfStdDev,
                                                   pfnProgress, pProgressData );
    }

    return CE_Failure;
}

/************************************************************************/
/* ==================================================================== */
/*                          VRTFuncSource                               */
/* ==================================================================== */
/************************************************************************/

/************************************************************************/
/*                           VRTFuncSource()                            */
/************************************************************************/

VRTFuncSource::VRTFuncSource() :
    pfnReadFunc(nullptr),
    pCBData(nullptr),
    eType(GDT_Byte),
    fNoDataValue(static_cast<float>(VRT_NODATA_UNSET))
{}

/************************************************************************/
/*                           ~VRTFuncSource()                           */
/************************************************************************/

VRTFuncSource::~VRTFuncSource() {}

/************************************************************************/
/*                           SerializeToXML()                           */
/************************************************************************/

CPLXMLNode *VRTFuncSource::SerializeToXML( CPL_UNUSED const char * pszVRTPath )
{
    return nullptr;
}

/************************************************************************/
/*                              RasterIO()                              */
/************************************************************************/

CPLErr
VRTFuncSource::RasterIO( GDALDataType /*eBandDataType*/,
                         int nXOff, int nYOff, int nXSize, int nYSize,
                         void *pData, int nBufXSize, int nBufYSize,
                         GDALDataType eBufType,
                         GSpacing nPixelSpace,
                         GSpacing nLineSpace,
                         GDALRasterIOExtraArg* /* psExtraArg */ )
{
    if( nPixelSpace*8 == GDALGetDataTypeSize( eBufType )
        && nLineSpace == nPixelSpace * nXSize
        && nBufXSize == nXSize && nBufYSize == nYSize
        && eBufType == eType )
    {
        return pfnReadFunc( pCBData,
                            nXOff, nYOff, nXSize, nYSize,
                            pData );
    }
    else
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "VRTFuncSource::RasterIO() - Irregular request." );
        CPLDebug("VRT", "Irregular request: %d,%d  %d,%d, %d,%d %d,%d %d,%d",
                static_cast<int>(nPixelSpace)*8,
                GDALGetDataTypeSize(eBufType),
                static_cast<int>(nLineSpace),
                static_cast<int>(nPixelSpace) * nXSize,
                nBufXSize, nXSize,
                nBufYSize, nYSize,
                static_cast<int>(eBufType),
                static_cast<int>(eType) );

        return CE_Failure;
    }
}

/************************************************************************/
/*                             GetMinimum()                             */
/************************************************************************/

double VRTFuncSource::GetMinimum( int /* nXSize */,
                                  int /* nYSize */,
                                  int *pbSuccess )
{
    *pbSuccess = FALSE;
    return 0;
}

/************************************************************************/
/*                             GetMaximum()                             */
/************************************************************************/

double VRTFuncSource::GetMaximum( int /* nXSize */,
                                  int /* nYSize */,
                                  int *pbSuccess )
{
    *pbSuccess = FALSE;
    return 0;
}

/************************************************************************/
/*                       ComputeRasterMinMax()                          */
/************************************************************************/

CPLErr VRTFuncSource::ComputeRasterMinMax( int /* nXSize */,
                                           int /* nYSize */,
                                           int /* bApproxOK */,
                                           double* /* adfMinMax */ )
{
    return CE_Failure;
}

/************************************************************************/
/*                         ComputeStatistics()                          */
/************************************************************************/

CPLErr VRTFuncSource::ComputeStatistics( int /* nXSize */,
                                         int /* nYSize */,
                                         int /* bApproxOK */,
                                         double * /* pdfMin */,
                                         double * /* pdfMax */,
                                         double * /* pdfMean */,
                                         double * /* pdfStdDev */,
                                         GDALProgressFunc /* pfnProgress */,
                                         void * /* pProgressData */ )
{
    return CE_Failure;
}

/************************************************************************/
/*                            GetHistogram()                            */
/************************************************************************/

CPLErr VRTFuncSource::GetHistogram( int /* nXSize */,
                                    int /* nYSize */,
                                    double /* dfMin */,
                                    double /* dfMax */,
                                    int /* nBuckets */,
                                    GUIntBig * /* panHistogram */,
                                    int /* bIncludeOutOfRange */,
                                    int /* bApproxOK */,
                                    GDALProgressFunc /* pfnProgress */,
                                    void * /* pProgressData */)
{
    return CE_Failure;
}

/************************************************************************/
/*                        VRTParseCoreSources()                         */
/************************************************************************/

VRTSource *VRTParseCoreSources( CPLXMLNode *psChild, const char *pszVRTPath,
                                void* pUniqueHandle,
                                std::map<CPLString, GDALDataset*>& oMapSharedSources )

{
    VRTSource * poSource = nullptr;

    if( EQUAL(psChild->pszValue,"AveragedSource")
        || (EQUAL(psChild->pszValue,"SimpleSource")
            && STARTS_WITH_CI(CPLGetXMLValue(psChild, "Resampling", "Nearest"),
                              "Aver")) )
    {
        poSource = new VRTAveragedSource();
    }
    else if( EQUAL(psChild->pszValue,"SimpleSource") )
    {
        poSource = new VRTSimpleSource();
    }
    else if( EQUAL(psChild->pszValue,"ComplexSource") )
    {
        poSource = new VRTComplexSource();
    }
    else
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "VRTParseCoreSources() - Unknown source : %s", psChild->pszValue );
        return nullptr;
    }

    if( poSource->XMLInit( psChild, pszVRTPath, pUniqueHandle,
                           oMapSharedSources ) == CE_None )
        return poSource;

    delete poSource;
    return nullptr;
}
/*! @endcond */
