CopperSpice API  1.7.2
QImageIOHandler Class Referenceabstract

The QImageIOHandler class defines the common image I/O interface for all image formats. More...

Inherited by QBmpHandler, QGifHandler, QIcoHandler, QJpegHandler, QPngHandler, QPpmHandler, QTiffHandler, QXbmHandler, and QXpmHandler.

Public Types

enum  ImageOption

Public Methods

QImageIOHandler ()

virtual ~QImageIOHandler ()

virtual bool canRead () = 0

virtual int currentImageNumber () const

virtual QRect currentImageRect () const

QIODevicedevice () const

QString format () const

virtual int imageCount ()

virtual bool jumpToImage (int imageNumber)

virtual bool jumpToNextImage ()

virtual int loopCount () const

virtual QString name () const

virtual int nextImageDelay () const

virtual QVariant option (ImageOption option)

virtual bool read (QImage *image) = 0

void setDevice (QIODevice *device)

void setFormat (const QString &format)

virtual void setOption (ImageOption option, const QVariant &value)

virtual bool supportsOption (ImageOption option) const

virtual bool write (const QImage &image)

Detailed Description

The QImageIOHandler class defines the common image I/O interface for all image formats in CopperSpice.

CopperSpice uses QImageIOHandler for reading and writing images through QImageReader and QImageWriter. You can also derive from this class to write your own image format handler using the CopperSpice plugin mechanism.

Call setDevice() to assign a device to the handler, and setFormat() to assign a format to it. One QImageIOHandler may support more than one image format. canRead() returns true if an image can be read from the device, and read() and write() return true if reading or writing an image was completed successfully.

QImageIOHandler also has support for animations formats, through the functions loopCount(), imageCount(), nextImageDelay() and currentImageNumber().

In order to determine what options an image handler supports, CopperSpice will call supportsOption() and setOption(). Make sure to reimplement these functions if you can provide support for any of the options in the ImageOption enum.

To write your own image handler, you must at least reimplement canRead() and read(). Then create a QImageIOPlugin that can create the handler. Finally, install your plugin, and QImageReader and QImageWriter will then automatically load the plugin, and start using it.

Member Enumeration Documentation

This enum describes the different options supported by QImageIOHandler. Some options are used to query an image for properties, and others are used to toggle the way in which an image should be written.

ConstantValueDescription
QImageIOHandler::Size0The original size of an image. A handler that supports this option is expected to read the size of the image from the image metadata, and return this size from option() as a QSize.
QImageIOHandler::ClipRect1The clip rect, or ROI (Region Of Interest). A handler that supports this option is expected to only read the provided QRect area from the original image in read(), before any other transformation is applied.
QImageIOHandler::ScaledSize4The scaled size of the image. A handler that supports this option is expected to scale the image to the provided size (a QSize), after applying any clip rect transformation (ClipRect). If the handler does not support this option, QImageReader will perform the scaling after the image has been read.
QImageIOHandler::ScaledClipRect3The scaled clip rect (or ROI, Region Of Interest) of the image. A handler that supports this option is expected to apply the provided clip rect (a QRect), after applying any scaling (ScaleSize) or regular clipping (ClipRect). If the handler does not support this option, QImageReader will apply the scaled clip rect after the image has been read.
QImageIOHandler::Description2The image description. Some image formats such as GIF and PNG, allow embedding of text or comments into the image data (e.g., for storing copyright information). The text is commonly stored in key-value pairs, but some formats store all text in one continuous block. QImageIOHandler returns the text as one QString, where keys and values are separated by a ':', and keys-value pairs are separated by two newlines (\n\n). For example, "Title: Sunset\n\nAuthor: Jim Smith\nSarah Jones\n\n". Formats which store text in a single block can use "Description" as the key.
QImageIOHandler::CompressionRatio5The compression ratio of the image data. A handler that supports this option is expected to set its compression rate depending on the value of this option (an int) when writing.
QImageIOHandler::Gamma6The gamma level of the image. A handler that supports this option is expected to set the image gamma level depending on the value of this option (a float) when writing.
QImageIOHandler::Quality7The quality level of the image. A handler that supports this option is expected to set the image quality level depending on the value of this option (an int) when writing.
QImageIOHandler::Name8The name of the image. A handler that supports this option is expected to read the name from the image metadata and return this as a QString, or when writing an image it is expected to store the name in the image metadata.
QImageIOHandler::SubType9The subtype of the image. A handler that supports this option can use the subtype value to help when reading and writing images. For example, a PPM handler may have a subtype value of "ppm" or "ppmraw".
QImageIOHandler::IncrementalReading10A handler that supports this option is expected to read the image in several passes, as if it was an animation. QImageReader will treat the image as an animation.
QImageIOHandler::Endianness11The endianness of the image. Certain image formats can be stored as BigEndian or LittleEndian. A handler that supports Endianness uses the value of this option to determine how the image should be stored.
QImageIOHandler::Animation12Image formats that support animation return true for this value in supportsOption(), otherwise false is returned.
QImageIOHandler::BackgroundColor13Certain image formats allow the background color to be specified. A handler that supports BackgroundColor initializes the background color to this option (a QColor) when reading an image.
QImageIOHandler::ImageFormat14The image's data format returned by the handler. This can be any of the formats listed in QImage::Format.

Constructor & Destructor Documentation

 QImageIOHandler::QImageIOHandler ( )

Constructs a QImageIOHandler object.

 QImageIOHandler::~QImageIOHandler ( )
virtual

Destructs the QImageIOHandler object.

Method Documentation

pure virtual

Returns true if an image can be read from the device (i.e., the image format is supported, the device can be read from and the initial header information suggests that the image can be read), otherwise returns false.

When reimplementing canRead(), make sure that the I/O device (device()) is left in its original state (e.g., by using peek() rather than read()).

 int QImageIOHandler::currentImageNumber ( ) const
virtual

For image formats that support animation, this function returns the sequence number of the current image in the animation. If this function is called before any image is read(), -1 is returned. The number of the first image in the sequence is 0.

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

 QRect QImageIOHandler::currentImageRect ( ) const
virtual

Returns the rect of the current image. If no rect is defined for the image, and empty QRect() is returned.

This function is useful for animations, where only parts of the frame may be updated at a time.

 QIODevice * QImageIOHandler::device ( ) const

Returns the device currently assigned to the QImageIOHandler. If not device has been assigned, 0 is returned.

setDevice()
 QString QImageIOHandler::format ( ) const

Returns the format that is currently assigned to QImageIOHandler. If no format has been assigned, an empty string is returned.

setFormat()
 int QImageIOHandler::imageCount ( )
virtual

For image formats that support animation, this function returns the number of images in the animation. If the image format does not support animation, or if it is unable to determine the number of images, 0 is returned.

The default implementation returns 1 if canRead() returns true, otherwise 0 is returned.

 bool QImageIOHandler::jumpToImage ( int imageNumber )
virtual

For image formats that support animation, this function jumps to the image whose sequence number is imageNumber. The next call to read() will attempt to read this image.

The default implementation does nothing, and returns false.

 bool QImageIOHandler::jumpToNextImage ( )
virtual

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

The default implementation does nothing, and returns false.

 int QImageIOHandler::loopCount ( ) const
virtual

For image formats that support animation, this function returns the number of times the animation should loop. If the image format does not support animation, 0 is returned.

 QString QImageIOHandler::name ( ) const
deprecatedvirtual
Deprecated:
 int QImageIOHandler::nextImageDelay ( ) const
virtual

For image formats that support animation, this function returns the number of milliseconds to wait until reading the next image. If the image format does not support animation, 0 is returned.

 QVariant QImageIOHandler::option ( ImageOption option )
virtual

Returns the value assigned to option as a QVariant. The type of the value depends on the option. For example, option(Size) returns a QSize variant.

setOption(), supportsOption()
 bool QImageIOHandler::read ( QImage * image )
pure virtual

Read an image from the device, and stores it in image. Returns true if the image is successfully read; otherwise returns false. For image formats that support incremental loading, and for animation formats, the image handler can assume that image points to the previous frame.

 void QImageIOHandler::setDevice ( QIODevice * device )

Sets the device of the QImageIOHandler to device. The image handler will use this device when reading and writing images. The device can only be set once and must be set before calling canRead(), read(), write(), etc. If you need to read multiple files, construct multiple instances of the appropriate QImageIOHandler subclass.

device()
 void QImageIOHandler::setFormat ( const QString & format )

Sets the format of the QImageIOHandler to format. The format is most useful for handlers that support multiple image formats.

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

Sets the option option with the value value.