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    41 

    42 /*!

    43     \class QImageIOHandler

    44     \brief The QImageIOHandler class defines the common image I/O

    45     interface for all image formats in Qt.

    46     \reentrant

    47 

    48     Qt uses QImageIOHandler for reading and writing images through

    49     QImageReader and QImageWriter. You can also derive from this class

    50     to write your own image format handler using Qt's plugin mechanism.

    51 

    52     Call setDevice() to assign a device to the handler, and

    53     setFormat() to assign a format to it. One QImageIOHandler may

    54     support more than one image format. canRead() returns true if an

    55     image can be read from the device, and read() and write() return

    56     true if reading or writing an image was completed successfully.

    57 

    58     QImageIOHandler also has support for animations formats, through

    59     the functions loopCount(), imageCount(), nextImageDelay() and

    60     currentImageNumber().

    61 

    62     In order to determine what options an image handler supports, Qt

    63     will call supportsOption() and setOption(). Make sure to

    64     reimplement these functions if you can provide support for any of

    65     the options in the ImageOption enum.

    66 

    67     To write your own image handler, you must at least reimplement

    68     canRead() and read(). Then create a QImageIOPlugin that

    69     can create the handler. Finally, install your plugin, and

    70     QImageReader and QImageWriter will then automatically load the

    71     plugin, and start using it.

    72 

    73     \sa QImageIOPlugin, QImageReader, QImageWriter

    74 */

    75 

    76 /*! \enum QImageIOHandler::ImageOption

    77 

    78     This enum describes the different options supported by

    79     QImageIOHandler.  Some options are used to query an image for

    80     properties, and others are used to toggle the way in which an

    81     image should be written.

    82 

    83     \value Size The original size of an image. A handler that supports

    84     this option is expected to read the size of the image from the

    85     image metadata, and return this size from option() as a QSize.

    86 

    87     \value ClipRect The clip rect, or ROI (Region Of Interest). A

    88     handler that supports this option is expected to only read the

    89     provided QRect area from the original image in read(), before any

    90     other transformation is applied.

    91 

    92     \value ScaledSize The scaled size of the image. A handler that

    93     supports this option is expected to scale the image to the

    94     provided size (a QSize), after applying any clip rect

    95     transformation (ClipRect). If the handler does not support this

    96     option, QImageReader will perform the scaling after the image has

    97     been read.

    98 

    99     \value ScaledClipRect The scaled clip rect (or ROI, Region Of

   100     Interest) of the image. A handler that supports this option is

   101     expected to apply the provided clip rect (a QRect), after applying

   102     any scaling (ScaleSize) or regular clipping (ClipRect). If the

   103     handler does not support this option, QImageReader will apply the

   104     scaled clip rect after the image has been read.

   105 

   106     \value Description The image description. Some image formats,

   107     such as GIF and PNG, allow embedding of text

   108     or comments into the image data (e.g., for storing copyright

   109     information). It's common that the text is stored in key-value

   110     pairs, but some formats store all text in one continuous block.

   111     QImageIOHandler returns the text as one

   112     QString, where keys and values are separated by a ':', and

   113     keys-value pairs are separated by two newlines (\\n\\n). For example,

   114     "Title: Sunset\\n\\nAuthor: Jim Smith\\nSarah Jones\\n\\n". Formats that

   115     store text in a single block can use "Description" as the key.

   116 

   117     \value CompressionRatio The compression ratio of the image data. A

   118     handler that supports this option is expected to set its

   119     compression rate depending on the value of this option (an int)

   120     when writing.

   121 

   122     \value Gamma The gamma level of the image. A handler that supports

   123     this option is expected to set the image gamma level depending on

   124     the value of this option (a float) when writing.

   125 

   126     \value Quality The quality level of the image. A handler that

   127     supports this option is expected to set the image quality level

   128     depending on the value of this option (an int) when writing.

   129 

   130     \value Name The name of the image. A handler that supports this

   131     option is expected to read the name from the image metadata and

   132     return this as a QString, or when writing an image it is expected

   133     to store the name in the image metadata.

   134 

   135     \value SubType The subtype of the image. A handler that supports

   136     this option can use the subtype value to help when reading and

   137     writing images. For example, a PPM handler may have a subtype

   138     value of "ppm" or "ppmraw".

   139 

   140     \value IncrementalReading A handler that supports this option is

   141     expected to read the image in several passes, as if it was an

   142     animation. QImageReader will treat the image as an animation.

   143 

   144     \value Endianness The endianness of the image. Certain image

   145     formats can be stored as BigEndian or LittleEndian. A handler that

   146     supports Endianness uses the value of this option to determine how

   147     the image should be stored.

   148 

   149     \value Animation Image formats that support animation return

   150     true for this value in supportsOption(); otherwise, false is returned.

   151 

   152     \value BackgroundColor Certain image formats allow the

   153     background color to be specified. A handler that supports

   154     BackgroundColor initializes the background color to this option

   155     (a QColor) when reading an image.

   156 

   157     \value ImageFormat The image's data format returned by the handler.

   158     This can be any of the formats listed in QImage::Format.

   159 */

   160 

   161 /*!

   162     \class QImageIOPlugin

   163     \brief The QImageIOPlugin class defines an interface for writing

   164     an image format plugin.

   165     \reentrant

   166 

   167     \ingroup plugins

   168 

   169     QImageIOPlugin is a factory for creating QImageIOHandler objects,

   170     which are used internally by QImageReader and QImageWriter to add

   171     support for different image formats to Qt.

   172 

   173     Writing an image I/O plugin is achieved by subclassing this

   174     base class, reimplementing the pure virtual functions capabilities(),

   175     create(), and keys(), and exporting the class with the

   176     Q_EXPORT_PLUGIN2() macro. See \l{How to Create Qt Plugins} for details.

   177 

   178     An image format plugin can support three capabilities: reading (\l

   179     CanRead), writing (\l CanWrite) and \e incremental reading (\l

   180     CanReadIncremental). Reimplement capabilities() in you subclass to

   181     expose the capabilities of your image format.

   182 

   183     create() should create an instance of your QImageIOHandler

   184     subclass, with the provided device and format properly set, and

   185     return this handler. You must also reimplement keys() so that Qt

   186     knows which image formats your plugin supports.

   187 

   188     Different plugins can support different capabilities. For example,

   189     you may have one plugin that supports reading the GIF format, and

   190     another that supports writing. Qt will select the correct plugin

   191     for the job, depending on the return value of capabilities(). If

   192     several plugins support the same capability, Qt will select one

   193     arbitrarily.

   194 

   195     \sa QImageIOHandler, {How to Create Qt Plugins}

   196 */

   197 

   198 /*!

   199     \enum QImageIOPlugin::Capability

   200 

   201     This enum describes the capabilities of a QImageIOPlugin.

   202 

   203     \value CanRead The plugin can read images.

   204     \value CanWrite The plugin can write images.

   205     \value CanReadIncremental The plugin can read images incrementally.

   206 */

   207 

   208 /*!

   209     \class QImageIOHandlerFactoryInterface

   210     \brief The QImageIOHandlerFactoryInterface class provides the factory

   211     interface for QImageIOPlugin.

   212     \reentrant

   213 

   214     \internal

   215 

   216     \sa QImageIOPlugin

   217 */

   218 

   219 #include "qimageiohandler.h"

   220 

   221 #include <qbytearray.h>

   222 #include <qimage.h>

   223 #include <qvariant.h>

   224 

   225 QT_BEGIN_NAMESPACE

   226 

   227 class QIODevice;

   228 

   229 class QImageIOHandlerPrivate

   230 {

   231     Q_DECLARE_PUBLIC(QImageIOHandler)

   232 public:

   233     QImageIOHandlerPrivate(QImageIOHandler *q);

   234     virtual ~QImageIOHandlerPrivate();

   235 

   236     QIODevice *device;

   237     mutable QByteArray format;

   238 

   239     QImageIOHandler *q_ptr;

   240 };

   241 

   242 QImageIOHandlerPrivate::QImageIOHandlerPrivate(QImageIOHandler *q)

   243 {

   244     device = 0;

   245     q_ptr = q;

   246 }

   247 

   248 QImageIOHandlerPrivate::~QImageIOHandlerPrivate()

   249 {

   250 }

   251 

   252 /*!

   253     Constructs a QImageIOHandler object.

   254 */

   255 QImageIOHandler::QImageIOHandler()

   256     : d_ptr(new QImageIOHandlerPrivate(this))

   257 {

   258 }

   259 

   260 /*! \internal

   261 

   262     Constructs a QImageIOHandler object, using the private member \a

   263     dd.

   264 */

   265 QImageIOHandler::QImageIOHandler(QImageIOHandlerPrivate &dd)

   266     : d_ptr(&dd)

   267 {

   268 }

   269 

   270 /*!

   271     Destructs the QImageIOHandler object.

   272 */

   273 QImageIOHandler::~QImageIOHandler()

   274 {

   275 }

   276 

   277 /*!

   278     Sets the device of the QImageIOHandler to \a device. The image

   279     handler will use this device when reading and writing images.

   280 

   281     The device can only be set once and must be set before calling

   282     canRead(), read(), write(), etc. If you need to read multiple

   283     files, construct multiple instances of the appropriate

   284     QImageIOHandler subclass.

   285 

   286     \sa device()

   287 */

   288 void QImageIOHandler::setDevice(QIODevice *device)

   289 {

   290     Q_D(QImageIOHandler);

   291     d->device = device;

   292 }

   293 

   294 /*!

   295     Returns the device currently assigned to the QImageIOHandler. If

   296     not device has been assigned, 0 is returned.

   297 */

   298 QIODevice *QImageIOHandler::device() const

   299 {

   300     Q_D(const QImageIOHandler);

   301     return d->device;

   302 }

   303 

   304 /*!

   305     Sets the format of the QImageIOHandler to \a format. The format is

   306     most useful for handlers that support multiple image formats.

   307 

   308     \sa format()

   309 */

   310 void QImageIOHandler::setFormat(const QByteArray &format)

   311 {

   312     Q_D(QImageIOHandler);

   313     d->format = format;

   314 }

   315 

   316 /*!

   317     Sets the format of the QImageIOHandler to \a format. The format is

   318     most useful for handlers that support multiple image formats.

   319 

   320     This function is declared const so that it can be called from canRead().

   321 

   322     \sa format()

   323 */

   324 void QImageIOHandler::setFormat(const QByteArray &format) const

   325 {

   326     Q_D(const QImageIOHandler);

   327     d->format = format;

   328 }

   329 

   330 /*!

   331     Returns the format that is currently assigned to

   332     QImageIOHandler. If no format has been assigned, an empty string

   333     is returned.

   334 

   335     \sa setFormat()

   336 */

   337 QByteArray QImageIOHandler::format() const

   338 {

   339     Q_D(const QImageIOHandler);

   340     return d->format;

   341 }

   342 

   343 /*!

   344     \fn bool QImageIOHandler::read(QImage *image)

   345 

   346     Read an image from the device, and stores it in \a image.

   347     Returns true if the image is successfully read; otherwise returns

   348     false.

   349 

   350     For image formats that support incremental loading, and for animation

   351     formats, the image handler can assume that \a image points to the

   352     previous frame.

   353 

   354     \sa canRead()

   355 */

   356 

   357 /*!

   358     \fn bool QImageIOHandler::canRead() const

   359 

   360     Returns true if an image can be read from the device (i.e., the

   361     image format is supported, the device can be read from and the

   362     initial header information suggests that the image can be read);

   363     otherwise returns false.

   364 

   365     When reimplementing canRead(), make sure that the I/O device

   366     (device()) is left in its original state (e.g., by using peek()

   367     rather than read()).

   368 

   369     \sa read(), QIODevice::peek()

   370 */

   371 

   372 /*!

   373     \obsolete

   374 

   375     Use format() instead.

   376 */

   377 

   378 QByteArray QImageIOHandler::name() const

   379 {

   380     return format();

   381 }

   382 

   383 /*!

   384     Writes the image \a image to the assigned device. Returns true on

   385     success; otherwise returns false.

   386 

   387     The default implementation does nothing, and simply returns false.

   388 */

   389 bool QImageIOHandler::write(const QImage &image)

   390 {

   391     Q_UNUSED(image);

   392     return false;

   393 }

   394 

   395 /*!

   396     Sets the option \a option with the value \a value.

   397 

   398     \sa option(), ImageOption

   399 */

   400 void QImageIOHandler::setOption(ImageOption option, const QVariant &value)

   401 {

   402     Q_UNUSED(option);

   403     Q_UNUSED(value);

   404 }

   405 

   406 /*!

   407     Returns the value assigned to \a option as a QVariant. The type of

   408     the value depends on the option. For example, option(Size) returns

   409     a QSize variant.

   410 

   411     \sa setOption(), supportsOption()

   412 */

   413 QVariant QImageIOHandler::option(ImageOption option) const

   414 {

   415     Q_UNUSED(option);

   416     return QVariant();

   417 }

   418 

   419 /*!

   420     Returns true if the QImageIOHandler supports the option \a option;

   421     otherwise returns false. For example, if the QImageIOHandler

   422     supports the \l Size option, supportsOption(Size) must return

   423     true.

   424 

   425     \sa setOption(), option()

   426 */

   427 bool QImageIOHandler::supportsOption(ImageOption option) const

   428 {

   429     Q_UNUSED(option);

   430     return false;

   431 }

   432 

   433 /*!

   434     For image formats that support animation, this function returns

   435     the sequence number of the current image in the animation. If

   436     this function is called before any image is read(), -1 is

   437     returned. The number of the first image in the sequence is 0.

   438     

   439     If the image format does not support animation, 0 is returned.

   440 

   441     \sa read()

   442 */

   443 int QImageIOHandler::currentImageNumber() const

   444 {

   445     return 0;

   446 }

   447 

   448 /*!

   449     Returns the rect of the current image. If no rect is defined for the

   450     image, and empty QRect() is returned.

   451 

   452     This function is useful for animations, where only parts of the frame

   453     may be updated at a time.

   454 */

   455 QRect QImageIOHandler::currentImageRect() const

   456 {

   457     return QRect();

   458 }

   459 

   460 /*!

   461     For image formats that support animation, this function returns

   462     the number of images in the animation. If the image format does

   463     not support animation, or if it is unable to determine the number

   464     of images, 0 is returned.

   465 

   466     The default implementation returns 1 if canRead() returns true;

   467     otherwise 0 is returned.

   468 */

   469 int QImageIOHandler::imageCount() const

   470 {

   471     return canRead() ? 1 : 0;

   472 }

   473 

   474 /*!

   475    For image formats that support animation, this function jumps to the

   476    next image.

   477 

   478    The default implementation does nothing, and returns false.

   479 */

   480 bool QImageIOHandler::jumpToNextImage()

   481 {

   482     return false;

   483 }

   484 

   485 /*!

   486    For image formats that support animation, this function jumps to the image

   487    whose sequence number is \a imageNumber. The next call to read() will

   488    attempt to read this image.

   489 

   490    The default implementation does nothing, and returns false.

   491 */

   492 bool QImageIOHandler::jumpToImage(int imageNumber)

   493 {

   494     Q_UNUSED(imageNumber);

   495     return false;

   496 }

   497 

   498 /*!

   499     For image formats that support animation, this function returns

   500     the number of times the animation should loop. If the image format

   501     does not support animation, 0 is returned.

   502 */

   503 int QImageIOHandler::loopCount() const

   504 {

   505     return 0;

   506 }

   507 

   508 /*!

   509     For image formats that support animation, this function returns

   510     the number of milliseconds to wait until reading the next

   511     image. If the image format does not support animation, 0 is

   512     returned.

   513 */

   514 int QImageIOHandler::nextImageDelay() const

   515 {

   516     return 0;

   517 }

   518 

   519 /*!

   520     Constructs an image plugin with the given \a parent. This is

   521     invoked automatically by the Q_EXPORT_PLUGIN2() macro.

   522 */

   523 QImageIOPlugin::QImageIOPlugin(QObject *parent)

   524     : QObject(parent)

   525 {

   526 }

   527 

   528 /*!

   529     Destroys the picture format plugin.

   530 

   531     You never have to call this explicitly. Qt destroys a plugin

   532     automatically when it is no longer used.

   533 */

   534 QImageIOPlugin::~QImageIOPlugin()

   535 {

   536 }

   537 

   538 /*! \fn QImageIOPlugin::capabilities(QIODevice *device, const QByteArray &format) const

   539 

   540     Returns the capabilities on the plugin, based on the data in \a

   541     device and the format \a format. For example, if the

   542     QImageIOHandler supports the BMP format, and the data in the

   543     device starts with the characters "BM", this function should

   544     return \l CanRead. If \a format is "bmp" and the handler supports

   545     both reading and writing, this function should return \l CanRead |

   546     \l CanWrite.

   547 */

   548 

   549 /*!

   550     \fn QImageIOPlugin::keys() const

   551 

   552     Returns the list of image keys this plugin supports.

   553 

   554     These keys are usually the names of the image formats that are implemented

   555     in the plugin (e.g., "jpg" or "gif").

   556 

   557     \sa capabilities()

   558 */

   559 

   560 /*!

   561     \fn QImageIOHandler *QImageIOPlugin::create(QIODevice *device, const QByteArray &format) const

   562 

   563     Creates and returns a QImageIOHandler subclass, with \a device

   564     and \a format set. The \a format must come from the list returned by keys().

   565     Format names are case sensitive.

   566 

   567     \sa keys()

   568 */

   569 

   570 QT_END_NAMESPACE