ImfHeader.cpp

///////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2004, Industrial Light & Magic, a division of Lucas
// Digital Ltd. LLC
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
// *       Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// *       Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// *       Neither the name of Industrial Light & Magic nor the names of
// its contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
///////////////////////////////////////////////////////////////////////////



//-----------------------------------------------------------------------------
//
//	class Header
//
//-----------------------------------------------------------------------------

#include <ImfHeader.h>
#include <ImfStdIO.h>
#include <ImfVersion.h>
#include <ImfCompressor.h>
#include <ImfMisc.h>
#include <ImfBoxAttribute.h>
#include <ImfChannelListAttribute.h>
#include <ImfChromaticitiesAttribute.h>
#include <ImfCompressionAttribute.h>
#include <ImfDoubleAttribute.h>
#include <ImfEnvmapAttribute.h>
#include <ImfFloatAttribute.h>
#include <ImfIntAttribute.h>
#include <ImfKeyCodeAttribute.h>
#include <ImfLineOrderAttribute.h>
#include <ImfMatrixAttribute.h>
#include <ImfOpaqueAttribute.h>
#include <ImfPreviewImageAttribute.h>
#include <ImfRationalAttribute.h>
#include <ImfStringAttribute.h>
#include <ImfStringVectorAttribute.h>
#include <ImfTileDescriptionAttribute.h>
#include <ImfTimeCodeAttribute.h>
#include <ImfVecAttribute.h>
#include "IlmThreadMutex.h"
#include "Iex.h"
#include <sstream>
#include <stdlib.h>
#include <time.h>


namespace Imf {

using namespace std;
using Imath::Box2i;
using Imath::V2i;
using Imath::V2f;
using IlmThread::Mutex;
using IlmThread::Lock;


namespace {

int maxImageWidth = 0;
int maxImageHeight = 0;
int maxTileWidth = 0;
int maxTileHeight = 0;


void
initialize (Header &header,
        const Box2i &displayWindow,
        const Box2i &dataWindow,
        float pixelAspectRatio,
        const V2f &screenWindowCenter,
        float screenWindowWidth,
        LineOrder lineOrder,
        Compression compression)
{
    header.insert ("displayWindow", Box2iAttribute (displayWindow));
    header.insert ("dataWindow", Box2iAttribute (dataWindow));
    header.insert ("pixelAspectRatio", FloatAttribute (pixelAspectRatio));
    header.insert ("screenWindowCenter", V2fAttribute (screenWindowCenter));
    header.insert ("screenWindowWidth", FloatAttribute (screenWindowWidth));
    header.insert ("lineOrder", LineOrderAttribute (lineOrder));
    header.insert ("compression", CompressionAttribute (compression));
    header.insert ("channels", ChannelListAttribute ());
}


bool
usesLongNames (const Header &header)
{
    //
    // If an OpenEXR file contains any attribute names, attribute type names
    // or channel names longer than 31 characters, then the file cannot be
    // read by older versions of the IlmImf library (up to OpenEXR 1.6.1).
    // Before writing the file header, we check if the header contains
    // any names longer than 31 characters; if it does, then we set the
    // LONG_NAMES_FLAG in the file version number.  Older versions of the
    // IlmImf library will refuse to read files that have the LONG_NAMES_FLAG
    // set.  Without the flag, older versions of the library would mis-
    // interpret the file as broken.
    //

    for (Header::ConstIterator i = header.begin();
         i != header.end();
         ++i)
    {
        if (strlen (i.name()) >= 32 || strlen (i.attribute().typeName()) >= 32)
            return true;
    }

    const ChannelList &channels = header.channels();

    for (ChannelList::ConstIterator i = channels.begin();
         i != channels.end();
         ++i)
    {
        if (strlen (i.name()) >= 32)
            return true;
    }

    return false;
}

template <size_t N>
void checkIsNullTerminated (const char (&str)[N], const char *what)
{
    for (int i = 0; i < N; ++i) {
        if (str[i] == '\0')
            return;
    }
    std::stringstream s;
    s << "Invalid " << what << ": it is more than " << (N - 1)
        << " characters long.";
    throw Iex::InputExc(s);
}

} // namespace


Header::Header (int width,
        int height,
        float pixelAspectRatio,
        const V2f &screenWindowCenter,
        float screenWindowWidth,
        LineOrder lineOrder,
        Compression compression)
:
    _map()
{
    staticInitialize();

    Box2i displayWindow (V2i (0, 0), V2i (width - 1, height - 1));

    initialize (*this,
        displayWindow,
        displayWindow,
        pixelAspectRatio,
        screenWindowCenter,
        screenWindowWidth,
        lineOrder,
        compression);
}


Header::Header (int width,
        int height,
        const Box2i &dataWindow,
        float pixelAspectRatio,
        const V2f &screenWindowCenter,
        float screenWindowWidth,
        LineOrder lineOrder,
        Compression compression)
:
    _map()
{
    staticInitialize();

    Box2i displayWindow (V2i (0, 0), V2i (width - 1, height - 1));

    initialize (*this,
        displayWindow,
        dataWindow,
        pixelAspectRatio,
        screenWindowCenter,
        screenWindowWidth,
        lineOrder,
        compression);
}


Header::Header (const Box2i &displayWindow,
        const Box2i &dataWindow,
        float pixelAspectRatio,
        const V2f &screenWindowCenter,
        float screenWindowWidth,
        LineOrder lineOrder,
        Compression compression)
:
    _map()
{
    staticInitialize();

    initialize (*this,
        displayWindow,
        dataWindow,
        pixelAspectRatio,
        screenWindowCenter,
        screenWindowWidth,
        lineOrder,
        compression);
}


Header::Header (const Header &other): _map()
{
    for (AttributeMap::const_iterator i = other._map.begin();
     i != other._map.end();
     ++i)
    {
    insert (*i->first, *i->second);
    }
}


Header::~Header ()
{
    for (AttributeMap::iterator i = _map.begin();
     i != _map.end();
     ++i)
    {
     delete i->second;
    }
}


Header &
Header::operator = (const Header &other)
{
    if (this != &other)
    {
    for (AttributeMap::iterator i = _map.begin();
         i != _map.end();
         ++i)
    {
         delete i->second;
    }

    _map.erase (_map.begin(), _map.end());

    for (AttributeMap::const_iterator i = other._map.begin();
         i != other._map.end();
         ++i)
    {
        insert (*i->first, *i->second);
    }
    }

    return *this;
}


void
Header::insert (const char name[], const Attribute &attribute)
{
    if (name[0] == 0)
    THROW (Iex::ArgExc, "Image attribute name cannot be an empty string.");

    AttributeMap::iterator i = _map.find (name);

    if (i == _map.end())
    {
    Attribute *tmp = attribute.copy();

    try
    {
        _map[name] = tmp;
    }
    catch (...)
    {
        delete tmp;
        throw;
    }
    }
    else
    {
    if (strcmp (i->second->typeName(), attribute.typeName()))
        THROW (Iex::TypeExc, "Cannot assign a value of "
                 "type \"" << attribute.typeName() << "\" "
                 "to image attribute \"" << name << "\" of "
                 "type \"" << i->second->typeName() << "\".");

    Attribute *tmp = attribute.copy();
    delete i->second;
    i->second = tmp;
    }
}


void
Header::insert (const string &name, const Attribute &attribute)
{
    insert (name.c_str(), attribute);
}


Attribute &
Header::operator [] (const char name[])
{
    AttributeMap::iterator i = _map.find (name);

    if (i == _map.end())
    THROW (Iex::ArgExc, "Cannot find image attribute \"" << name << "\".");

    return *i->second;
}


const Attribute &
Header::operator [] (const char name[]) const
{
    AttributeMap::const_iterator i = _map.find (name);

    if (i == _map.end())
    THROW (Iex::ArgExc, "Cannot find image attribute \"" << name << "\".");

    return *i->second;
}


Attribute &
Header::operator [] (const string &name)
{
    return this->operator[] (name.c_str());
}


const Attribute &
Header::operator [] (const string &name) const
{
    return this->operator[] (name.c_str());
}


Header::Iterator
Header::begin ()
{
    return _map.begin();
}


Header::ConstIterator
Header::begin () const
{
    return _map.begin();
}


Header::Iterator
Header::end ()
{
    return _map.end();
}


Header::ConstIterator
Header::end () const
{
    return _map.end();
}


Header::Iterator
Header::find (const char name[])
{
    return _map.find (name);
}


Header::ConstIterator
Header::find (const char name[]) const
{
    return _map.find (name);
}


Header::Iterator
Header::find (const string &name)
{
    return find (name.c_str());
}


Header::ConstIterator
Header::find (const string &name) const
{
    return find (name.c_str());
}


Imath::Box2i &
Header::displayWindow ()
{
    return static_cast <Box2iAttribute &>
    ((*this)["displayWindow"]).value();
}


const Imath::Box2i &
Header::displayWindow () const
{
    return static_cast <const Box2iAttribute &>
    ((*this)["displayWindow"]).value();
}


Imath::Box2i &
Header::dataWindow ()
{
    return static_cast <Box2iAttribute &>
    ((*this)["dataWindow"]).value();
}


const Imath::Box2i &
Header::dataWindow () const
{
    return static_cast <const Box2iAttribute &>
    ((*this)["dataWindow"]).value();
}


float &
Header::pixelAspectRatio ()
{
    return static_cast <FloatAttribute &>
    ((*this)["pixelAspectRatio"]).value();
}


const float &
Header::pixelAspectRatio () const
{
    return static_cast <const FloatAttribute &>
    ((*this)["pixelAspectRatio"]).value();
}


Imath::V2f &
Header::screenWindowCenter ()
{
    return static_cast <V2fAttribute &>
    ((*this)["screenWindowCenter"]).value();
}


const Imath::V2f &
Header::screenWindowCenter () const
{
    return static_cast <const V2fAttribute &>
    ((*this)["screenWindowCenter"]).value();
}


float &
Header::screenWindowWidth ()
{
    return static_cast <FloatAttribute &>
    ((*this)["screenWindowWidth"]).value();
}


const float &
Header::screenWindowWidth () const
{
    return static_cast <const FloatAttribute &>
    ((*this)["screenWindowWidth"]).value();
}


ChannelList &
Header::channels ()
{
    return static_cast <ChannelListAttribute &>
    ((*this)["channels"]).value();
}


const ChannelList &
Header::channels () const
{
    return static_cast <const ChannelListAttribute &>
    ((*this)["channels"]).value();
}


LineOrder &
Header::lineOrder ()
{
    return static_cast <LineOrderAttribute &>
    ((*this)["lineOrder"]).value();
}


const LineOrder &
Header::lineOrder () const
{
    return static_cast <const LineOrderAttribute &>
    ((*this)["lineOrder"]).value();
}


Compression &
Header::compression ()
{
    return static_cast <CompressionAttribute &>
    ((*this)["compression"]).value();
}


const Compression &
Header::compression () const
{
    return static_cast <const CompressionAttribute &>
    ((*this)["compression"]).value();
}


void
Header::setTileDescription(const TileDescription& td)
{
    insert ("tiles", TileDescriptionAttribute (td));
}


bool
Header::hasTileDescription() const
{
    return findTypedAttribute <TileDescriptionAttribute> ("tiles") != 0;
}


TileDescription &
Header::tileDescription ()
{
    return typedAttribute <TileDescriptionAttribute> ("tiles").value();
}


const TileDescription &
Header::tileDescription () const
{
    return typedAttribute <TileDescriptionAttribute> ("tiles").value();
}

void
Header::setPreviewImage (const PreviewImage &pi)
{
    insert ("preview", PreviewImageAttribute (pi));
}


PreviewImage &
Header::previewImage ()
{
    return typedAttribute <PreviewImageAttribute> ("preview").value();
}


const PreviewImage &
Header::previewImage () const
{
    return typedAttribute <PreviewImageAttribute> ("preview").value();
}


bool
Header::hasPreviewImage () const
{
    return findTypedAttribute <PreviewImageAttribute> ("preview") != 0;
}


void
Header::sanityCheck (bool isTiled) const
{
    //
    // The display window and the data window must each
    // contain at least one pixel.  In addition, the
    // coordinates of the window corners must be small
    // enough to keep expressions like max-min+1 or
    // max+min from overflowing.
    //

    const Box2i &displayWindow = this->displayWindow();

    if (displayWindow.min.x > displayWindow.max.x ||
    displayWindow.min.y > displayWindow.max.y ||
    displayWindow.min.x <= -(INT_MAX / 2) ||
    displayWindow.min.y <= -(INT_MAX / 2) ||
    displayWindow.max.x >=  (INT_MAX / 2) ||
    displayWindow.max.y >=  (INT_MAX / 2))
    {
    throw Iex::ArgExc ("Invalid display window in image header.");
    }

    const Box2i &dataWindow = this->dataWindow();

    if (dataWindow.min.x > dataWindow.max.x ||
    dataWindow.min.y > dataWindow.max.y ||
    dataWindow.min.x <= -(INT_MAX / 2) ||
    dataWindow.min.y <= -(INT_MAX / 2) ||
    dataWindow.max.x >=  (INT_MAX / 2) ||
    dataWindow.max.y >=  (INT_MAX / 2))
    {
    throw Iex::ArgExc ("Invalid data window in image header.");
    }

    if (maxImageWidth > 0 &&
    maxImageWidth < dataWindow.max.x - dataWindow.min.x + 1)
    {
    THROW (Iex::ArgExc, "The width of the data window exceeds the "
                "maximum width of " << maxImageWidth << "pixels.");
    }

    if (maxImageHeight > 0 &&
    maxImageHeight < dataWindow.max.y - dataWindow.min.y + 1)
    {
    THROW (Iex::ArgExc, "The width of the data window exceeds the "
                "maximum width of " << maxImageHeight << "pixels.");
    }

    //
    // The pixel aspect ratio must be greater than 0.
    // In applications, numbers like the the display or
    // data window dimensions are likely to be multiplied
    // or divided by the pixel aspect ratio; to avoid
    // arithmetic exceptions, we limit the pixel aspect
    // ratio to a range that is smaller than theoretically
    // possible (real aspect ratios are likely to be close
    // to 1.0 anyway).
    //

    float pixelAspectRatio = this->pixelAspectRatio();

    const float MIN_PIXEL_ASPECT_RATIO = 1e-6f;
    const float MAX_PIXEL_ASPECT_RATIO = 1e+6f;

    if (pixelAspectRatio < MIN_PIXEL_ASPECT_RATIO ||
    pixelAspectRatio > MAX_PIXEL_ASPECT_RATIO)
    {
    throw Iex::ArgExc ("Invalid pixel aspect ratio in image header.");
    }

    //
    // The screen window width must not be less than 0.
    // The size of the screen window can vary over a wide
    // range (fish-eye lens to astronomical telescope),
    // so we can't limit the screen window width to a
    // small range.
    //

    float screenWindowWidth = this->screenWindowWidth();

    if (screenWindowWidth < 0)
    throw Iex::ArgExc ("Invalid screen window width in image header.");

    //
    // If the file is tiled, verify that the tile description has resonable
    // values and check to see if the lineOrder is one of the predefined 3.
    // If the file is not tiled, then the lineOrder can only be INCREASING_Y
    // or DECREASING_Y.
    //

    LineOrder lineOrder = this->lineOrder();

    if (isTiled)
    {
    if (!hasTileDescription())
    {
        throw Iex::ArgExc ("Tiled image has no tile "
                   "description attribute.");
    }

    const TileDescription &tileDesc = tileDescription();

    if (tileDesc.xSize <= 0 || tileDesc.ySize <= 0)
        throw Iex::ArgExc ("Invalid tile size in image header.");

    if (maxTileWidth > 0 &&
        maxTileWidth < tileDesc.xSize)
    {
        THROW (Iex::ArgExc, "The width of the tiles exceeds the maximum "
                "width of " << maxTileWidth << "pixels.");
    }

    if (maxTileHeight > 0 &&
        maxTileHeight < tileDesc.ySize)
    {
        THROW (Iex::ArgExc, "The width of the tiles exceeds the maximum "
                "width of " << maxTileHeight << "pixels.");
    }

    if (tileDesc.mode != ONE_LEVEL &&
        tileDesc.mode != MIPMAP_LEVELS &&
        tileDesc.mode != RIPMAP_LEVELS)
        throw Iex::ArgExc ("Invalid level mode in image header.");

    if (tileDesc.roundingMode != ROUND_UP &&
        tileDesc.roundingMode != ROUND_DOWN)
        throw Iex::ArgExc ("Invalid level rounding mode in image header.");

    if (lineOrder != INCREASING_Y &&
        lineOrder != DECREASING_Y &&
        lineOrder != RANDOM_Y)
        throw Iex::ArgExc ("Invalid line order in image header.");
    }
    else
    {
    if (lineOrder != INCREASING_Y &&
        lineOrder != DECREASING_Y)
        throw Iex::ArgExc ("Invalid line order in image header.");
    }

    //
    // The compression method must be one of the predefined values.
    //

    if (!isValidCompression (this->compression()))
    throw Iex::ArgExc ("Unknown compression type in image header.");

    //
    // Check the channel list:
    //
    // If the file is tiled then for each channel, the type must be one of the
    // predefined values, and the x and y sampling must both be 1.
    //
    // If the file is not tiled then for each channel, the type must be one
    // of the predefined values, the x and y coordinates of the data window's
    // upper left corner must be divisible by the x and y subsampling factors,
    // and the width and height of the data window must be divisible by the
    // x and y subsampling factors.
    //

    const ChannelList &channels = this->channels();

    if (isTiled)
    {
    for (ChannelList::ConstIterator i = channels.begin();
         i != channels.end();
         ++i)
    {
        if (i.channel().type != UINT &&
        i.channel().type != HALF &&
        i.channel().type != FLOAT)
        {
        THROW (Iex::ArgExc, "Pixel type of \"" << i.name() << "\" "
                        "image channel is invalid.");
        }

        if (i.channel().xSampling != 1)
        {
        THROW (Iex::ArgExc, "The x subsampling factor for the "
                    "\"" << i.name() << "\" channel "
                    "is not 1.");
        }

        if (i.channel().ySampling != 1)
        {
        THROW (Iex::ArgExc, "The y subsampling factor for the "
                    "\"" << i.name() << "\" channel "
                    "is not 1.");
        }
    }
    }
    else
    {
    for (ChannelList::ConstIterator i = channels.begin();
         i != channels.end();
         ++i)
    {
        if (i.channel().type != UINT &&
        i.channel().type != HALF &&
        i.channel().type != FLOAT)
        {
        THROW (Iex::ArgExc, "Pixel type of \"" << i.name() << "\" "
                        "image channel is invalid.");
        }

        if (i.channel().xSampling < 1)
        {
        THROW (Iex::ArgExc, "The x subsampling factor for the "
                    "\"" << i.name() << "\" channel "
                    "is invalid.");
        }

        if (i.channel().ySampling < 1)
        {
        THROW (Iex::ArgExc, "The y subsampling factor for the "
                    "\"" << i.name() << "\" channel "
                    "is invalid.");
        }

        if (dataWindow.min.x % i.channel().xSampling)
        {
        THROW (Iex::ArgExc, "The minimum x coordinate of the "
                    "image's data window is not a multiple "
                    "of the x subsampling factor of "
                    "the \"" << i.name() << "\" channel.");
        }

        if (dataWindow.min.y % i.channel().ySampling)
        {
        THROW (Iex::ArgExc, "The minimum y coordinate of the "
                    "image's data window is not a multiple "
                    "of the y subsampling factor of "
                    "the \"" << i.name() << "\" channel.");
        }

        if ((dataWindow.max.x - dataWindow.min.x + 1) %
            i.channel().xSampling)
        {
        THROW (Iex::ArgExc, "Number of pixels per row in the "
                    "image's data window is not a multiple "
                    "of the x subsampling factor of "
                    "the \"" << i.name() << "\" channel.");
        }

        if ((dataWindow.max.y - dataWindow.min.y + 1) %
            i.channel().ySampling)
        {
        THROW (Iex::ArgExc, "Number of pixels per column in the "
                    "image's data window is not a multiple "
                    "of the y subsampling factor of "
                    "the \"" << i.name() << "\" channel.");
        }
    }
    }
}


void
Header::setMaxImageSize (int maxWidth, int maxHeight)
{
    maxImageWidth = maxWidth;
    maxImageHeight = maxHeight;
}


void
Header::setMaxTileSize (int maxWidth, int maxHeight)
{
    maxTileWidth = maxWidth;
    maxTileHeight = maxHeight;
}


Int64
Header::writeTo (OStream &os, bool isTiled) const
{
    //
    // Write a "magic number" to identify the file as an image file.
    // Write the current file format version number.
    //

    Xdr::write <StreamIO> (os, MAGIC);

    int version = EXR_VERSION;

    if (isTiled)
        version |= TILED_FLAG;

    if (usesLongNames (*this))
        version |= LONG_NAMES_FLAG;

    Xdr::write <StreamIO> (os, version);

    //
    // Write all attributes.  If we have a preview image attribute,
    // keep track of its position in the file.
    //

    Int64 previewPosition = 0;

    const Attribute *preview =
        findTypedAttribute <PreviewImageAttribute> ("preview");

    for (ConstIterator i = begin(); i != end(); ++i)
    {
    //
    // Write the attribute's name and type.
    //

    Xdr::write <StreamIO> (os, i.name());
    Xdr::write <StreamIO> (os, i.attribute().typeName());

    //
    // Write the size of the attribute value,
    // and the value itself.
    //

    StdOSStream oss;
    i.attribute().writeValueTo (oss, version);

    std::string s = oss.str();
    Xdr::write <StreamIO> (os, (int) s.length());

    if (&i.attribute() == preview)
        previewPosition = os.tellp();

    os.write (s.data(), s.length());
    }

    //
    // Write zero-length attribute name to mark the end of the header.
    //

    Xdr::write <StreamIO> (os, "");

    return previewPosition;
}


void
Header::readFrom (IStream &is, int &version)
{
    //
    // Read the magic number and the file format version number.
    // Then check if we can read the rest of this file.
    //

    int magic;

    Xdr::read <StreamIO> (is, magic);
    Xdr::read <StreamIO> (is, version);

    if (magic != MAGIC)
    {
    throw Iex::InputExc ("File is not an image file.");
    }

    if (getVersion (version) != EXR_VERSION)
    {
    THROW (Iex::InputExc, "Cannot read "
                  "version " << getVersion (version) << " "
                  "image files.  Current file format version "
                  "is " << EXR_VERSION << ".");
    }

    if (!supportsFlags (getFlags (version)))
    {
    THROW (Iex::InputExc, "The file format version number's flag field "
                  "contains unrecognized flags.");
    }

    //
    // Read all attributes.
    //

    while (true)
    {
    //
    // Read the name of the attribute.
    // A zero-length attribute name indicates the end of the header.
    //

    char name[Name::SIZE];
    Xdr::read <StreamIO> (is, Name::MAX_LENGTH, name);

    if (name[0] == 0)
        break;

    checkIsNullTerminated (name, "attribute name");

    //
    // Read the attribute type and the size of the attribute value.
    //

    char typeName[Name::SIZE];
    int size;

    Xdr::read <StreamIO> (is, Name::MAX_LENGTH, typeName);
    checkIsNullTerminated (typeName, "attribute type name");
    Xdr::read <StreamIO> (is, size);

    AttributeMap::iterator i = _map.find (name);

    if (i != _map.end())
    {
        //
        // The attribute already exists (for example,
        // because it is a predefined attribute).
        // Read the attribute's new value from the file.
        //

        if (strncmp (i->second->typeName(), typeName, sizeof (typeName)))
        THROW (Iex::InputExc, "Unexpected type for image attribute "
                      "\"" << name << "\".");

        i->second->readValueFrom (is, size, version);
    }
    else
    {
        //
        // The new attribute does not exist yet.
        // If the attribute type is of a known type,
        // read the attribute value.  If the attribute
        // is of an unknown type, read its value and
        // store it as an OpaqueAttribute.
        //

        Attribute *attr;

        if (Attribute::knownType (typeName))
        attr = Attribute::newAttribute (typeName);
        else
        attr = new OpaqueAttribute (typeName);

        try
        {
        attr->readValueFrom (is, size, version);
        _map[name] = attr;
        }
        catch (...)
        {
        delete attr;
        throw;
        }
    }
    }
}


void
staticInitialize ()
{
    static Mutex criticalSection;
    Lock lock (criticalSection);

    static bool initialized = false;

    if (!initialized)
    {
    //
    // One-time initialization -- register
    // some predefined attribute types.
    //

    Box2fAttribute::registerAttributeType();
    Box2iAttribute::registerAttributeType();
    ChannelListAttribute::registerAttributeType();
    CompressionAttribute::registerAttributeType();
    ChromaticitiesAttribute::registerAttributeType();
    DoubleAttribute::registerAttributeType();
    EnvmapAttribute::registerAttributeType();
    FloatAttribute::registerAttributeType();
    IntAttribute::registerAttributeType();
    KeyCodeAttribute::registerAttributeType();
    LineOrderAttribute::registerAttributeType();
    M33dAttribute::registerAttributeType();
    M33fAttribute::registerAttributeType();
    M44dAttribute::registerAttributeType();
    M44fAttribute::registerAttributeType();
    PreviewImageAttribute::registerAttributeType();
    RationalAttribute::registerAttributeType();
    StringAttribute::registerAttributeType();
        StringVectorAttribute::registerAttributeType();
    TileDescriptionAttribute::registerAttributeType();
    TimeCodeAttribute::registerAttributeType();
    V2dAttribute::registerAttributeType();
    V2fAttribute::registerAttributeType();
    V2iAttribute::registerAttributeType();
    V3dAttribute::registerAttributeType();
    V3fAttribute::registerAttributeType();
    V3iAttribute::registerAttributeType();

    initialized = true;
    }
}


} // namespace Imf