/******************************************************************************
 *
 * Project:  DDS Driver
 * Purpose:  Implement GDAL DDS Support
 * Author:   Alan Boudreault, aboudreault@mapgears.com
 *
 ******************************************************************************
 * Copyright (c) 2013, Alan Boudreault
 * Copyright (c) 2013,2019, Even Rouault <even dot rouault at spatialys.com>
 *
 * SPDX-License-Identifier: MIT
 ******************************************************************************/

#include "crunch_headers.h"
#include "gdal_frmts.h"
#include "gdal_pam.h"
#include "ddsdrivercore.h"

#include <algorithm>

using namespace crnlib;

enum
{
    DDS_COLOR_TYPE_RGB,
    DDS_COLOR_TYPE_RGB_ALPHA
};

constexpr uint32_t cDXTBlockSize = 4;

/************************************************************************/
/* ==================================================================== */
/*                              DDSDataset                              */
/* ==================================================================== */
/************************************************************************/

class DDSDataset final : public GDALPamDataset
{
    friend class DDSRasterBand;

    VSILFILE *fp = nullptr;
    int nCurrentYBlock = -1;
    crn_format nFormat = cCRNFmtInvalid;
    uint32_t nBytesPerBlock = 0;
    uint32_t nCompressedSizePerStripe = 0;
    void *pCompressedBuffer = nullptr;
    void *pUncompressedBuffer = nullptr;

    DDSDataset() = default;
    ~DDSDataset();

  public:
    static GDALDataset *Open(GDALOpenInfo *poOpenInfo);
    static GDALDataset *CreateCopy(const char *pszFilename,
                                   GDALDataset *poSrcDS, int bStrict,
                                   char **papszOptions,
                                   GDALProgressFunc pfnProgress,
                                   void *pProgressData);
};

/************************************************************************/
/* ==================================================================== */
/*                            DDSRasterBand                             */
/* ==================================================================== */
/************************************************************************/

class DDSRasterBand final : public GDALPamRasterBand
{
  protected:
    CPLErr IReadBlock(int, int, void *) override;

    GDALColorInterp GetColorInterpretation() override
    {
        return static_cast<GDALColorInterp>(GCI_RedBand + nBand - 1);
    }

  public:
    DDSRasterBand(DDSDataset *poDS, int nBand);
};

/************************************************************************/
/* ==================================================================== */
/*                         DDSDatasetAllDecoded                         */
/* ==================================================================== */
/************************************************************************/

class DDSDatasetAllDecoded final : public GDALPamDataset
{
    friend class DDSRasterBandAllDecoded;

    std::vector<crn_uint32 *> m_pImages{};
    crn_texture_desc m_tex_desc{};

    DDSDatasetAllDecoded() = default;
    ~DDSDatasetAllDecoded();

  public:
    static GDALDataset *Open(GDALOpenInfo *poOpenInfo);
};

/************************************************************************/
/* ==================================================================== */
/*                        DDSRasterBandAllDecoded                       */
/* ==================================================================== */
/************************************************************************/

class DDSRasterBandAllDecoded final : public GDALPamRasterBand
{
  protected:
    CPLErr IReadBlock(int, int, void *) override;

    GDALColorInterp GetColorInterpretation() override
    {
        return static_cast<GDALColorInterp>(GCI_RedBand + nBand - 1);
    }

  public:
    DDSRasterBandAllDecoded(DDSDatasetAllDecoded *poDS, int nBand);
};

/************************************************************************/
/*                           ~DDSDataset()                              */
/************************************************************************/

DDSDataset::~DDSDataset()
{
    if (fp)
        VSIFCloseL(fp);
    CPLFree(pCompressedBuffer);
    CPLFree(pUncompressedBuffer);
}

/************************************************************************/
/*                           DDSRasterBand()                            */
/************************************************************************/

DDSRasterBand::DDSRasterBand(DDSDataset *poDSIn, int nBandIn)
{
    poDS = poDSIn;
    nBand = nBandIn;
    nBlockXSize = poDSIn->GetRasterXSize();
    nBlockYSize = cDXTBlockSize;
    eDataType = GDT_Byte;
}

/************************************************************************/
/*                             IReadBlock()                             */
/************************************************************************/

CPLErr DDSRasterBand::IReadBlock(int, int nYBlock, void *pImage)
{
    auto poGDS = cpl::down_cast<DDSDataset *>(poDS);
    const size_t nUncompressedBandOffset =
        static_cast<size_t>(nRasterXSize) * cDXTBlockSize;
    if (nYBlock != poGDS->nCurrentYBlock)
    {
        auto nFileOffset =
            strlen(DDS_SIGNATURE) + sizeof(crnlib::DDSURFACEDESC2) +
            static_cast<vsi_l_offset>(poGDS->nCompressedSizePerStripe) *
                nYBlock;
        VSIFSeekL(poGDS->fp, nFileOffset, SEEK_SET);
        if (VSIFReadL(poGDS->pCompressedBuffer, poGDS->nCompressedSizePerStripe,
                      1, poGDS->fp) != 1)
        {
            return CE_Failure;
        }

        const uint32_t num_blocks_x =
            (nRasterXSize + cDXTBlockSize - 1) / cDXTBlockSize;
        const GByte *pabySrc =
            static_cast<const GByte *>(poGDS->pCompressedBuffer);
        crn_uint32
            anDstPixels[cDXTBlockSize *
                        cDXTBlockSize];  // A << 24 | B << 16 | G << 8 | R
        GByte *pabyDst = static_cast<GByte *>(poGDS->pUncompressedBuffer);
        const bool bHasAlpha = poGDS->nBands == 4;
        for (uint32_t block_x = 0; block_x < num_blocks_x; block_x++)
        {
            const void *pSrc_block =
                pabySrc + static_cast<size_t>(block_x) * poGDS->nBytesPerBlock;
            if (!crn_decompress_block(pSrc_block, anDstPixels, poGDS->nFormat))
            {
                return CE_Failure;
            }
            const crn_uint32 *pUncompressedPixels = anDstPixels;
            for (uint32_t y = 0; y < cDXTBlockSize; y++)
            {
                for (uint32_t x = 0; x < cDXTBlockSize; x++)
                {
                    const uint32_t actual_x = block_x * cDXTBlockSize + x;
                    if (actual_x < static_cast<uint32_t>(nRasterXSize))
                    {
                        const auto nRGBAPixel = *pUncompressedPixels;
                        const auto offsetInBand =
                            actual_x + static_cast<size_t>(y) * nRasterXSize;
                        pabyDst[offsetInBand] =
                            static_cast<GByte>(nRGBAPixel & 0xff);
                        pabyDst[nUncompressedBandOffset + offsetInBand] =
                            static_cast<GByte>((nRGBAPixel >> 8) & 0xff);
                        pabyDst[2 * nUncompressedBandOffset + offsetInBand] =
                            static_cast<GByte>((nRGBAPixel >> 16) & 0xff);
                        if (bHasAlpha)
                        {
                            pabyDst[3 * nUncompressedBandOffset +
                                    offsetInBand] =
                                static_cast<GByte>((nRGBAPixel >> 24) & 0xff);
                        }
                    }
                    pUncompressedPixels++;
                }
            }
        }
        poGDS->nCurrentYBlock = nYBlock;
    }
    const GByte *pabyUncompressed =
        static_cast<const GByte *>(poGDS->pUncompressedBuffer);
    memcpy(pImage, pabyUncompressed + (nBand - 1) * nUncompressedBandOffset,
           nUncompressedBandOffset);
    return CE_None;
}

/************************************************************************/
/*                                Open()                                */
/************************************************************************/

GDALDataset *DDSDataset::Open(GDALOpenInfo *poOpenInfo)
{
    if (!DDSDriverIdentify(poOpenInfo))
        return nullptr;

    crnlib::DDSURFACEDESC2 ddsDesc;
    memcpy(&ddsDesc, poOpenInfo->pabyHeader + strlen(DDS_SIGNATURE),
           sizeof(ddsDesc));
#ifdef CPL_MSB
    {
        GUInt32 *ddsDescAsUInt32 = reinterpret_cast<GUInt32 *>(&ddsDesc);
        for (size_t i = 0; i < sizeof(ddsDesc) / sizeof(GUInt32); ++i)
        {
            CPL_LSBPTR32(&ddsDescAsUInt32[i]);
        }
    }
#endif
    if (ddsDesc.dwWidth == 0 || ddsDesc.dwWidth > INT_MAX ||
        ddsDesc.dwHeight == 0 || ddsDesc.dwHeight > INT_MAX)
    {
        return nullptr;
    }
    if (ddsDesc.ddpfPixelFormat.dwSize != sizeof(crnlib::DDPIXELFORMAT))
    {
        CPLDebug("DDS", "Unsupported ddpfPixelFormat.dwSize = %u",
                 ddsDesc.ddpfPixelFormat.dwSize);
        return nullptr;
    }

    if (ddsDesc.ddpfPixelFormat.dwFlags != DDPF_FOURCC)
    {
#ifdef DEBUG
        CPLDebug("DDS",
                 "Unsupported ddpfPixelFormat.dwFlags in regular path: %u",
                 ddsDesc.ddpfPixelFormat.dwFlags);
#endif
        return DDSDatasetAllDecoded::Open(poOpenInfo);
    }
    crn_format fmt = cCRNFmtInvalid;
    switch (ddsDesc.ddpfPixelFormat.dwFourCC)
    {
        case PIXEL_FMT_DXT1:
        case PIXEL_FMT_DXT1A:
            fmt = cCRNFmtDXT1;
            break;
        case PIXEL_FMT_DXT2:
        case PIXEL_FMT_DXT3:
            fmt = cCRNFmtDXT3;
            break;
        case PIXEL_FMT_DXT4:
        case PIXEL_FMT_DXT5:
            fmt = cCRNFmtDXT5;
            break;
        // case PIXEL_FMT_DXT5A:
        //     fmt = cCRNFmtDXT5A;
        //     break;
        case PIXEL_FMT_ETC1:
            fmt = cCRNFmtETC1;
            break;
        // case PIXEL_FMT_3DC:
        //     fmt = cCRNFmtDXN_YX;
        //     break;
        // case PIXEL_FMT_DXN:
        //     fmt = cCRNFmtDXN_XY;
        //     break;
        default:
        {
#ifdef DEBUG
            char szFourCC[5] = {};
            memcpy(&szFourCC[0], &ddsDesc.ddpfPixelFormat.dwFourCC, 4);
            CPLDebug("DDS", "Unhandled FOURCC = %s in regular path", szFourCC);
#endif
            return DDSDatasetAllDecoded::Open(poOpenInfo);
        }
    }

    const uint32_t bytesPerBlock = crn_get_bytes_per_dxt_block(fmt);
    const uint32_t num_blocks_x =
        (ddsDesc.dwWidth + cDXTBlockSize - 1) / cDXTBlockSize;
    const uint32_t num_blocks_y =
        (ddsDesc.dwHeight + cDXTBlockSize - 1) / cDXTBlockSize;
    const uint32_t compressed_size_per_row = num_blocks_x * bytesPerBlock;
    const vsi_l_offset nCompressedDataSize =
        static_cast<vsi_l_offset>(compressed_size_per_row) * num_blocks_y;

    VSIFSeekL(poOpenInfo->fpL, 0, SEEK_END);
    if (VSIFTellL(poOpenInfo->fpL) < strlen(DDS_SIGNATURE) +
                                         sizeof(crnlib::DDSURFACEDESC2) +
                                         nCompressedDataSize)
    {
        CPLDebug("DDS", "File too small");
        return nullptr;
    }
    void *pCompressedBuffer = VSI_MALLOC_VERBOSE(compressed_size_per_row);
    const int l_nBands = fmt == cCRNFmtETC1 ? 3 : 4;
    void *pUncompressedBuffer =
        VSI_MALLOC3_VERBOSE(ddsDesc.dwWidth, cDXTBlockSize, l_nBands);
    if (pCompressedBuffer == nullptr || pUncompressedBuffer == nullptr)
    {
        VSIFree(pCompressedBuffer);
        VSIFree(pUncompressedBuffer);
        return nullptr;
    }

    DDSDataset *poDS = new DDSDataset();
    poDS->fp = poOpenInfo->fpL;
    poOpenInfo->fpL = nullptr;
    poDS->nBytesPerBlock = bytesPerBlock;
    poDS->nFormat = fmt;
    poDS->nCompressedSizePerStripe = compressed_size_per_row;
    poDS->pCompressedBuffer = pCompressedBuffer;
    poDS->pUncompressedBuffer = pUncompressedBuffer;
    poDS->nRasterXSize = static_cast<int>(ddsDesc.dwWidth);
    poDS->nRasterYSize = static_cast<int>(ddsDesc.dwHeight);
    poDS->GDALDataset::SetMetadataItem(
        "COMPRESSION", crn_get_format_string(fmt), "IMAGE_STRUCTURE");
    poDS->GDALDataset::SetMetadataItem("INTERLEAVE", "PIXEL",
                                       "IMAGE_STRUCTURE");
    for (int i = 0; i < l_nBands; i++)
    {
        poDS->SetBand(i + 1, new DDSRasterBand(poDS, i + 1));
    }

    return poDS;
}

/************************************************************************/
/*                        ~DDSDatasetAllDecoded()                       */
/************************************************************************/

DDSDatasetAllDecoded::~DDSDatasetAllDecoded()
{
    crn_free_all_images(&m_pImages[0], m_tex_desc);
}

/************************************************************************/
/*                        DDSRasterBandAllDecoded()                     */
/************************************************************************/

DDSRasterBandAllDecoded::DDSRasterBandAllDecoded(DDSDatasetAllDecoded *poDSIn,
                                                 int nBandIn)
{
    poDS = poDSIn;
    nBand = nBandIn;
    nBlockXSize = poDSIn->GetRasterXSize();
    nBlockYSize = 1;
    eDataType = GDT_Byte;
}

/************************************************************************/
/*                             IReadBlock()                             */
/************************************************************************/

CPLErr DDSRasterBandAllDecoded::IReadBlock(int, int nYBlock, void *pImage)
{
    auto poGDS = cpl::down_cast<DDSDatasetAllDecoded *>(poDS);
    GByte *pabyData = static_cast<GByte *>(pImage);
    const int nShift = (nBand - 1) * 8;
    for (int i = 0; i < nRasterXSize; i++)
    {
        pabyData[i] = static_cast<GByte>(
            (poGDS->m_pImages[0][i + nYBlock * nRasterXSize] >> nShift) & 0xff);
    }
    return CE_None;
}

/************************************************************************/
/*                                Open()                                */
/************************************************************************/

GDALDataset *DDSDatasetAllDecoded::Open(GDALOpenInfo *poOpenInfo)
{
    VSIFSeekL(poOpenInfo->fpL, 0, SEEK_END);
    std::vector<GByte> data;
    const auto nFileSize = VSIFTellL(poOpenInfo->fpL);
    if (nFileSize > 100 * 1024 * 1024)
        return nullptr;
    try
    {
        data.resize(static_cast<size_t>(nFileSize));
    }
    catch (const std::exception &e)
    {
        CPLError(CE_Failure, CPLE_OutOfMemory, "%s", e.what());
        return nullptr;
    }
    VSIFSeekL(poOpenInfo->fpL, 0, SEEK_SET);
    VSIFReadL(&data[0], 1, data.size(), poOpenInfo->fpL);

    std::vector<crn_uint32 *> pImages;
    pImages.resize(cCRNMaxFaces * cCRNMaxLevels);
    crn_texture_desc tex_desc;
    const bool bRet = crn_decompress_dds_to_images(
        data.data(), static_cast<crn_uint32>(data.size()), &pImages[0],
        tex_desc);
#ifdef DEBUG
    CPLDebug("DDS", "w=%u h=%u faces=%u levels=%u fourCC=%c%c%c%c",
             tex_desc.m_width, tex_desc.m_height, tex_desc.m_faces,
             tex_desc.m_levels, static_cast<char>(tex_desc.m_fmt_fourcc & 0xff),
             static_cast<char>((tex_desc.m_fmt_fourcc >> 8) & 0xff),
             static_cast<char>((tex_desc.m_fmt_fourcc >> 16) & 0xff),
             static_cast<char>((tex_desc.m_fmt_fourcc >> 24) & 0xff));
#endif
    if (!bRet)
    {
        CPLDebug("DDS", "crn_decompress_dds_to_images() failed");
        return nullptr;
    }
    auto poDS = new DDSDatasetAllDecoded();
    poDS->nRasterXSize = static_cast<int>(tex_desc.m_width);
    poDS->nRasterYSize = static_cast<int>(tex_desc.m_height);
    poDS->m_tex_desc = tex_desc;
    poDS->m_pImages = std::move(pImages);
    constexpr int NBANDS = 4;
    poDS->GDALDataset::SetMetadataItem("INTERLEAVE", "PIXEL",
                                       "IMAGE_STRUCTURE");
    for (int i = 0; i < NBANDS; i++)
    {
        poDS->SetBand(i + 1, new DDSRasterBandAllDecoded(poDS, i + 1));
    }

    return poDS;
}

/************************************************************************/
/*                             CreateCopy()                             */
/************************************************************************/

GDALDataset *DDSDataset::CreateCopy(const char *pszFilename,
                                    GDALDataset *poSrcDS, int bStrict,
                                    char **papszOptions,
                                    GDALProgressFunc pfnProgress,
                                    void *pProgressData)

{
    int nBands = poSrcDS->GetRasterCount();

    /* -------------------------------------------------------------------- */
    /*      Some rudimentary checks                                         */
    /* -------------------------------------------------------------------- */
    if (nBands != 3 && nBands != 4)
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "DDS driver doesn't support %d bands. Must be 3 (rgb) \n"
                 "or 4 (rgba) bands.\n",
                 nBands);

        return nullptr;
    }

    if (poSrcDS->GetRasterBand(1)->GetRasterDataType() != GDT_Byte)
    {
        CPLError(
            (bStrict) ? CE_Failure : CE_Warning, CPLE_NotSupported,
            "DDS driver doesn't support data type %s. "
            "Only eight bit (Byte) bands supported. %s\n",
            GDALGetDataTypeName(poSrcDS->GetRasterBand(1)->GetRasterDataType()),
            (bStrict) ? "" : "Defaulting to Byte");

        if (bStrict)
            return nullptr;
    }

    /* -------------------------------------------------------------------- */
    /*      Setup some parameters.                                          */
    /* -------------------------------------------------------------------- */
    int nColorType = 0;

    if (nBands == 3)
        nColorType = DDS_COLOR_TYPE_RGB;
    else if (nBands == 4)
        nColorType = DDS_COLOR_TYPE_RGB_ALPHA;

    /* -------------------------------------------------------------------- */
    /*      Create the dataset.                                             */
    /* -------------------------------------------------------------------- */
    VSILFILE *fpImage = VSIFOpenL(pszFilename, "wb");
    if (fpImage == nullptr)
    {
        CPLError(CE_Failure, CPLE_OpenFailed, "Unable to create dds file %s.\n",
                 pszFilename);
        return nullptr;
    }

    /* -------------------------------------------------------------------- */
    /*      Create the Crunch compressor                                    */
    /* -------------------------------------------------------------------- */

    /* Default values */
    crn_format fmt = cCRNFmtDXT3;
    crn_dxt_quality dxt_quality = cCRNDXTQualityNormal;
    bool srgb_colorspace = true;
    bool dxt1a_transparency = true;
    // bool generate_mipmaps = true;

    /* Check the texture format */
    const char *pszFormat = CSLFetchNameValue(papszOptions, "FORMAT");

    if (pszFormat)
    {
        if (EQUAL(pszFormat, "dxt1"))
            fmt = cCRNFmtDXT1;
        else if (EQUAL(pszFormat, "dxt1a"))
            fmt = cCRNFmtDXT1;
        else if (EQUAL(pszFormat, "dxt3"))
            fmt = cCRNFmtDXT3;
        else if (EQUAL(pszFormat, "dxt5"))
            fmt = cCRNFmtDXT5;
        else if (EQUAL(pszFormat, "etc1"))
            fmt = cCRNFmtETC1;
        else
        {
            CPLError(CE_Failure, CPLE_AppDefined,
                     "Illegal FORMAT value '%s', should be DXT1, DXT1A, DXT3, "
                     "DXT5 or ETC1",
                     pszFormat);
            return nullptr;
        }
    }

    /* Check the compression quality */
    const char *pszQuality = CSLFetchNameValue(papszOptions, "QUALITY");

    if (pszQuality)
    {
        if (EQUAL(pszQuality, "SUPERFAST"))
            dxt_quality = cCRNDXTQualitySuperFast;
        else if (EQUAL(pszQuality, "FAST"))
            dxt_quality = cCRNDXTQualityFast;
        else if (EQUAL(pszQuality, "NORMAL"))
            dxt_quality = cCRNDXTQualityNormal;
        else if (EQUAL(pszQuality, "BETTER"))
            dxt_quality = cCRNDXTQualityBetter;
        else if (EQUAL(pszQuality, "UBER"))
            dxt_quality = cCRNDXTQualityUber;
        else
        {
            CPLError(CE_Failure, CPLE_AppDefined,
                     "Illegal QUALITY value '%s', should be SUPERFAST, FAST, "
                     "NORMAL, BETTER or UBER.",
                     pszQuality);
            return nullptr;
        }
    }

    const int nXSize = poSrcDS->GetRasterXSize();
    const int nYSize = poSrcDS->GetRasterYSize();

    crn_comp_params comp_params;
    comp_params.m_format = fmt;
    comp_params.m_dxt_quality = dxt_quality;
    comp_params.set_flag(cCRNCompFlagPerceptual, srgb_colorspace);
    comp_params.set_flag(cCRNCompFlagDXT1AForTransparency, dxt1a_transparency);

    crn_block_compressor_context_t pContext =
        crn_create_block_compressor(comp_params);

    /* -------------------------------------------------------------------- */
    /*      Write the DDS header to the file.                               */
    /* -------------------------------------------------------------------- */

    VSIFWriteL(DDS_SIGNATURE, 1, strlen(DDS_SIGNATURE), fpImage);

    crnlib::DDSURFACEDESC2 ddsDesc;
    memset(&ddsDesc, 0, sizeof(ddsDesc));
    ddsDesc.dwSize = sizeof(ddsDesc);
    ddsDesc.dwFlags = DDSD_CAPS | DDSD_HEIGHT | DDSD_WIDTH | DDSD_MIPMAPCOUNT |
                      DDSD_PIXELFORMAT | DDSD_DEPTH;
    ddsDesc.dwWidth = nXSize;
    ddsDesc.dwHeight = nYSize;
    ddsDesc.dwMipMapCount = 1;

    ddsDesc.ddpfPixelFormat.dwSize = sizeof(crnlib::DDPIXELFORMAT);
    ddsDesc.ddpfPixelFormat.dwFlags = DDPF_FOURCC;
    ddsDesc.ddpfPixelFormat.dwFourCC = crn_get_format_fourcc(fmt);
    ddsDesc.ddsCaps.dwCaps = DDSCAPS_TEXTURE;

    // Set pitch/linearsize field (some DDS readers require this field to be
    // non-zero).
    uint32_t bits_per_pixel = crn_get_format_bits_per_texel(fmt);
    ddsDesc.lPitch = (((ddsDesc.dwWidth + 3) & ~3U) *
                      ((ddsDesc.dwHeight + 3) & ~3U) * bits_per_pixel) >>
                     3;
    ddsDesc.dwFlags |= DDSD_LINEARSIZE;

#ifdef CPL_MSB
    {
        GUInt32 *ddsDescAsUInt32 = reinterpret_cast<GUInt32 *>(&ddsDesc);
        for (size_t i = 0; i < sizeof(ddsDesc) / sizeof(GUInt32); ++i)
        {
            CPL_LSBPTR32(&ddsDescAsUInt32[i]);
        }
    }
#endif
    VSIFWriteL(&ddsDesc, 1, sizeof(ddsDesc), fpImage);

    /* -------------------------------------------------------------------- */
    /*      Loop over image, compressing image data.                        */
    /* -------------------------------------------------------------------- */
    const uint32_t bytesPerBlock = crn_get_bytes_per_dxt_block(fmt);
    CPLErr eErr = CE_None;
    const uint32_t nYNumBlocks = (nYSize + cDXTBlockSize - 1) / cDXTBlockSize;
    const uint32_t num_blocks_x = (nXSize + cDXTBlockSize - 1) / cDXTBlockSize;
    const uint32_t total_compressed_size = num_blocks_x * bytesPerBlock;

    void *pCompressed_data = CPLMalloc(total_compressed_size);
    GByte *pabyScanlines = (GByte *)CPLMalloc(nBands * nXSize * cDXTBlockSize);
    crn_uint32 *pixels = (crn_uint32 *)CPLMalloc(sizeof(crn_uint32) *
                                                 cDXTBlockSize * cDXTBlockSize);
    crn_uint32 *src_image = nullptr;
    if (nColorType == DDS_COLOR_TYPE_RGB)
        src_image = (crn_uint32 *)CPLMalloc(sizeof(crn_uint32) * nXSize *
                                            cDXTBlockSize);

    for (uint32_t iLine = 0; iLine < nYNumBlocks && eErr == CE_None; iLine++)
    {
        const uint32_t size_y =
            (iLine * cDXTBlockSize + cDXTBlockSize) < (uint32_t)nYSize
                ? cDXTBlockSize
                : (cDXTBlockSize - ((iLine * cDXTBlockSize + cDXTBlockSize) -
                                    (uint32_t)nYSize));

        eErr =
            poSrcDS->RasterIO(GF_Read, 0, iLine * cDXTBlockSize, nXSize, size_y,
                              pabyScanlines, nXSize, size_y, GDT_Byte, nBands,
                              nullptr, nBands, nBands * nXSize, 1, nullptr);

        if (eErr != CE_None)
            break;

        crn_uint32 *pSrc_image = nullptr;
        if (nColorType == DDS_COLOR_TYPE_RGB_ALPHA)
            pSrc_image = (crn_uint32 *)pabyScanlines;
        else if (nColorType == DDS_COLOR_TYPE_RGB)
        { /* crunch needs 32bits integers */
            int nPixels = nXSize * cDXTBlockSize;
            for (int i = 0; i < nPixels; ++i)
            {
                int y = (i * 3);
                src_image[i] = (255U << 24) | (pabyScanlines[y + 2] << 16) |
                               (pabyScanlines[y + 1] << 8) | pabyScanlines[y];
            }

            pSrc_image = &(src_image[0]);
        }

        for (crn_uint32 block_x = 0; block_x < num_blocks_x; block_x++)
        {
            // Exact block from image, clamping at the sides of non-divisible by
            // 4 images to avoid artifacts.
            crn_uint32 *pDst_pixels = pixels;
            for (uint32_t y = 0; y < cDXTBlockSize; y++)
            {
                const uint32_t actual_y = std::min(y, size_y - 1U);
                for (uint32_t x = 0; x < cDXTBlockSize; x++)
                {
                    const uint32_t actual_x =
                        std::min(nXSize - 1U, (block_x * cDXTBlockSize) + x);
                    *pDst_pixels++ = pSrc_image[actual_x + actual_y * nXSize];
                }
            }

            // Compress the DXTn block.
            crn_compress_block(pContext, pixels,
                               static_cast<crn_uint8 *>(pCompressed_data) +
                                   block_x * bytesPerBlock);
        }

        VSIFWriteL(pCompressed_data, 1, total_compressed_size, fpImage);

        if (!pfnProgress((iLine + 1) / (double)nYNumBlocks, nullptr,
                         pProgressData))
        {
            eErr = CE_Failure;
            CPLError(CE_Failure, CPLE_UserInterrupt,
                     "User terminated CreateCopy()");
        }
    }

    CPLFree(src_image);
    CPLFree(pixels);
    CPLFree(pCompressed_data);
    CPLFree(pabyScanlines);
    crn_free_block_compressor(pContext);
    pContext = nullptr;

    VSIFCloseL(fpImage);

    if (eErr != CE_None)
        return nullptr;

    GDALOpenInfo oOpenInfo(pszFilename, GA_ReadOnly);
    return Open(&oOpenInfo);
}

/************************************************************************/
/*                          GDALRegister_DDS()                          */
/************************************************************************/

void GDALRegister_DDS()
{
    if (GDALGetDriverByName(DRIVER_NAME) != nullptr)
        return;

    GDALDriver *poDriver = new GDALDriver();
    DDSDriverSetCommonMetadata(poDriver);

    poDriver->pfnOpen = DDSDataset::Open;
    poDriver->pfnCreateCopy = DDSDataset::CreateCopy;

    GetGDALDriverManager()->RegisterDriver(poDriver);
}
