com.trolltech.qt.gui
Class QImageReader

java.lang.Object
  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.gui.QImageReader
All Implemented Interfaces:
QtJambiInterface

public class QImageReader
extends QtJambiObject

The QImageReader class provides a format independent interface for reading images from files or other devices. The most common way to read images is through QImage and QPixmap's constructors, or by calling QImage::load() and QPixmap::load(). QImageReader is a specialized class which gives you more control when reading images. For example, you can read an image into a specific size by calling setScaledSize(), and you can select a clip rect, effectively loading only parts of an image, by calling setClipRect(). Depending on the underlying support in the image format, this can save memory and speed up loading of images.

To read an image, you start by constructing a QImageReader object. Pass either a file name or a device pointer, and the image format to QImageReader's constructor. You can then set several options, such as the clip rect (by calling setClipRect()) and scaled size (by calling setScaledSize()). canRead() returns the image if the QImageReader can read the image (i.e., the image format is supported and the device is open for reading). Call read() to read the image.

If any error occurs when reading the image, read() will return a null QImage. You can then call error() to find the type of error that occurred, or errorString() to get a human readable description of what went wrong.

Call supportedImageFormats() for a list of formats that QImageReader can read. QImageReader supports all built-in image formats, in addition to any image format plugins that support reading.

QImageReader autodetects the image format by default, by looking at the provided (optional) format string, the file name suffix, and the data stream contents. You can enable or disable this feature, by calling setAutoDetectImageFormat().

See also:
QImageWriter, QImageIOHandler, and QImageIOPlugin.


Nested Class Summary
static class QImageReader.ImageReaderError
          This enum describes the different types of errors that can occur when reading images with QImageReader.
 
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9
 
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal
 
Field Summary
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
QImageReader()
          Constructs an empty QImageReader object.
QImageReader(QIODevice device)
          Constructs a QImageReader object with the device device and the image format format.
QImageReader(QIODevice device, QByteArray format)
          Constructs a QImageReader object with the device device and the image format format.
QImageReader(java.lang.String fileName)
          Constructs a QImageReader object with the file name fileName and the image format format.
QImageReader(java.lang.String fileName, QByteArray format)
          Constructs a QImageReader object with the file name fileName and the image format format.
 
Method Summary
 boolean autoDetectImageFormat()
          Returns true if image format autodetection is enabled on this image reader; otherwise returns false.
 QColor backgroundColor()
          Returns the background color that's used when reading an image.
 boolean canRead()
          Returns true if an image can be read for the device (i.
 QRect clipRect()
          Returns the clip rect (also known as the ROI, or Region Of Interest) of the image.
 int currentImageNumber()
          For image formats that support animation, this function returns the sequence number of the current frame.
 QRect currentImageRect()
          For image formats that support animation, this function returns the rect for the current frame.
 QIODevice device()
          Returns the device currently assigned to QImageReader, or 0 if no device has been assigned.
 QImageReader.ImageReaderError error()
          Returns the type of error that occurred last.
 java.lang.String errorString()
          Returns a human readable description of the last error that occurred.
 java.lang.String fileName()
          If the currently assigned device is a QFile, or if setFileName() has been called, this function returns the name of the file QImageReader reads from.
 QByteArray format()
          Returns the format QImageReader uses for reading images.
 int imageCount()
          For image formats that support animation, this function returns the total number of images in the animation.
 QImage.Format imageFormat()
          Returns the format of the image, without actually reading the image contents.
static QByteArray imageFormat(QIODevice device)
          If supported, this function returns the image format of the device device.
static QByteArray imageFormat(java.lang.String fileName)
          If supported, this function returns the image format of the file fileName.
 boolean jumpToImage(int imageNumber)
          For image formats that support animation, this function skips to the image whose sequence number is imageNumber, returning true if successful or false if the corresponding image cannot be found.
 boolean jumpToNextImage()
          For image formats that support animation, this function steps over the current image, returning true if successful or false if there is no following image in the animation.
 int loopCount()
          For image formats that support animation, this function returns the number of times the animation should loop.
 int nextImageDelay()
          For image formats that support animation, this function returns the number of milliseconds to wait until displaying the next frame in the animation.
 int quality()
          Returns the quality level of the image.
 QImage read()
          Reads an image from the device.
 QRect scaledClipRect()
          Returns the scaled clip rect of the image.
 QSize scaledSize()
          Returns the scaled size of the image.
 void setAutoDetectImageFormat(boolean enabled)
          If enabled is true, image format autodetection is enabled; otherwise, it is disabled.
 void setBackgroundColor(QColor color)
          Sets the background color to color.
 void setClipRect(QRect rect)
          Sets the image clip rect (also known as the ROI, or Region Of Interest) to rect.
 void setDevice(QIODevice device)
          Sets QImageReader's device to device.
 void setFileName(java.lang.String fileName)
          Sets the file name of QImageReader to fileName.
 void setFormat(QByteArray format)
          Sets the format QImageReader will use when reading images, to format.
 void setQuality(int quality)
          This is an image format specific function that sets the quality level of the image to quality.
 void setScaledClipRect(QRect rect)
          Sets the scaled clip rect to rect.
 void setScaledSize(QSize size)
          Sets the scaled size of the image to size.
 QSize size()
          Returns the size of the image, without actually reading the image contents.
static java.util.List supportedImageFormats()
          Returns the list of image formats supported by QImageReader.
 boolean supportsAnimation()
          Returns true if the image format supports animation; otherwise, false is returned.
 boolean supportsOption(QImageIOHandler.ImageOption option)
          Returns true if the reader supports option; otherwise returns false.
 java.lang.String text(java.lang.String key)
          Returns the image text associated with key.
 java.util.List textKeys()
          Returns the text keys for this image.
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
__qt_signalInitialization
 
Methods inherited from class java.lang.Object
clone, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Constructor Detail

QImageReader

public QImageReader()
Constructs an empty QImageReader object. Before reading an image, call setDevice() or setFileName().


QImageReader

public QImageReader(QIODevice device)
Constructs a QImageReader object with the device device and the image format format.


QImageReader

public QImageReader(QIODevice device,
                    QByteArray format)
Constructs a QImageReader object with the device device and the image format format.


QImageReader

public QImageReader(java.lang.String fileName)
Constructs a QImageReader object with the file name fileName and the image format format.

See also:
setFileName().


QImageReader

public QImageReader(java.lang.String fileName,
                    QByteArray format)
Constructs a QImageReader object with the file name fileName and the image format format.

See also:
setFileName().

Method Detail

autoDetectImageFormat

public final boolean autoDetectImageFormat()
Returns true if image format autodetection is enabled on this image reader; otherwise returns false. By default, autodetection is enabled.

See also:
setAutoDetectImageFormat().


backgroundColor

public final QColor backgroundColor()
Returns the background color that's used when reading an image. If the image format does not support setting the background color an invalid color is returned.

See also:
setBackgroundColor(), and read().


canRead

public final boolean canRead()
Returns true if an image can be read for the device (i. ., the image format is supported, and the device seems to contain valid data); otherwise returns false.

canRead() is a lightweight function that only does a quick test to see if the image data is valid. read() may still return false after canRead() returns true, if the image data is corrupt.

For images that support animation, canRead() returns false when all frames have been read.

See also:
read(), and supportedImageFormats().


clipRect

public final QRect clipRect()
Returns the clip rect (also known as the ROI, or Region Of Interest) of the image. If no clip rect has been set, an invalid QRect is returned.

See also:
setClipRect().


currentImageNumber

public final int currentImageNumber()
For image formats that support animation, this function returns the sequence number of the current frame. Otherwise, -1 is returned.

See also:
supportsAnimation(), and QImageIOHandler::currentImageNumber().


currentImageRect

public final QRect currentImageRect()
For image formats that support animation, this function returns the rect for the current frame. Otherwise, a null rect is returned.

See also:
supportsAnimation(), and QImageIOHandler::currentImageRect().


device

public final QIODevice device()
Returns the device currently assigned to QImageReader, or 0 if no device has been assigned.

See also:
setDevice().


error

public final QImageReader.ImageReaderError error()
Returns the type of error that occurred last.

See also:
ImageReaderError , and errorString().


errorString

public final java.lang.String errorString()
Returns a human readable description of the last error that occurred.

See also:
error().


fileName

public final java.lang.String fileName()
If the currently assigned device is a QFile, or if setFileName() has been called, this function returns the name of the file QImageReader reads from. Otherwise (i.e., if no device has been assigned or the device is not a QFile), an empty QString is returned.

See also:
setFileName(), and setDevice().


format

public final QByteArray format()
Returns the format QImageReader uses for reading images.

You can call this function after assigning a device to the reader to determine the format of the device. For example:

        QImageReader reader = new QImageReader("image.png");
        // reader.format() == "png"
If the reader cannot read any image from the device (e.g., there is no image there, or the image has already been read), or if the format is unsupported, this function returns an empty QByteArray().

See also:
setFormat(), and supportedImageFormats().


imageCount

public final int imageCount()
For image formats that support animation, this function returns the total number of images in the animation.

Certain animation formats do not support this feature, in which case 0 is returned.

See also:
supportsAnimation(), and QImageIOHandler::imageCount().


imageFormat

public final QImage.Format imageFormat()
Returns the format of the image, without actually reading the image contents. The format describes the image format QImageReader::read() returns, not the format of the actual image.

If the image format does not support this feature, this function returns an invalid format.

See also:
QImageIOHandler::ImageOption , QImageIOHandler::option(), and QImageIOHandler::supportsOption().


jumpToImage

public final boolean jumpToImage(int imageNumber)
For image formats that support animation, this function skips to the image whose sequence number is imageNumber, returning true if successful or false if the corresponding image cannot be found.

The next call to read() will attempt to read this image.

See also:
jumpToNextImage(), and QImageIOHandler::jumpToImage().


jumpToNextImage

public final boolean jumpToNextImage()
For image formats that support animation, this function steps over the current image, returning true if successful or false if there is no following image in the animation.

The default implementation calls read(), then discards the resulting image, but the image handler may have a more efficient way of implementing this operation.

See also:
jumpToImage(), and QImageIOHandler::jumpToNextImage().


loopCount

public final int loopCount()
For image formats that support animation, this function returns the number of times the animation should loop. Otherwise, it returns -1.

See also:
supportsAnimation(), and QImageIOHandler::loopCount().


nextImageDelay

public final int nextImageDelay()
For image formats that support animation, this function returns the number of milliseconds to wait until displaying the next frame in the animation. Otherwise, 0 is returned.

See also:
supportsAnimation(), and QImageIOHandler::nextImageDelay().


quality

public final int quality()
Returns the quality level of the image.

See also:
setQuality().


read

public final QImage read()
Reads an image from the device. On success, the image that was read is returned; otherwise, a null QImage is returned. You can then call error() to find the type of error that occurred, or errorString() to get a human readable description of the error.

For image formats that support animation, calling read() repeatedly will return the next frame. When all frames have been read, a null image will be returned.

See also:
canRead(), supportedImageFormats(), supportsAnimation(), and QMovie.


scaledClipRect

public final QRect scaledClipRect()
Returns the scaled clip rect of the image.

See also:
setScaledClipRect().


scaledSize

public final QSize scaledSize()
Returns the scaled size of the image.

See also:
setScaledSize().


setAutoDetectImageFormat

public final void setAutoDetectImageFormat(boolean enabled)
If enabled is true, image format autodetection is enabled; otherwise, it is disabled. By default, autodetection is enabled.

QImageReader uses an extensive approach to detecting the image format; firstly, if you pass a file name to QImageReader, it will attempt to detect the file extension if the given file name does not point to an existing file, by appending supported default extensions to the given file name, one at a time. It then uses the following approach to detect the image format:

By disabling image format autodetection, QImageReader will only query the plugins and built-in handlers based on the format string (i.e., no file name extensions are tested).

See also:
autoDetectImageFormat(), QImageIOHandler::canRead(), and QImageIOPlugin::capabilities().


setBackgroundColor

public final void setBackgroundColor(QColor color)
Sets the background color to color. Image formats that support this operation are expected to initialize the background to color before reading an image.

See also:
backgroundColor(), and read().


setClipRect

public final void setClipRect(QRect rect)
Sets the image clip rect (also known as the ROI, or Region Of Interest) to rect. The coordinates of rect are relative to the untransformed image size, as returned by size().

See also:
clipRect(), setScaledSize(), and setScaledClipRect().


setDevice

public final void setDevice(QIODevice device)
Sets QImageReader's device to device. If a device has already been set, the old device is removed from QImageReader and is otherwise left unchanged.

If the device is not already open, QImageReader will attempt to open the device in QIODevice::ReadOnly mode by calling open(). Note that this does not work for certain devices, such as QProcess, QTcpSocket and QUdpSocket, where more logic is required to open the device.

See also:
device(), and setFileName().


setFileName

public final void setFileName(java.lang.String fileName)
Sets the file name of QImageReader to fileName. Internally, QImageReader will create a QFile object and open it in QIODevice::ReadOnly mode, and use this when reading images.

If fileName does not include a file extension (e.g., .png or .bmp), QImageReader will cycle through all supported extensions until it finds a matching file.

See also:
fileName(), setDevice(), and supportedImageFormats().


setFormat

public final void setFormat(QByteArray format)
Sets the format QImageReader will use when reading images, to format. format is a case insensitive text string. Example:
        QImageReader reader = new QImageReader();
        reader.setFormat(new QByteArray("png")); // same as reader.setFormat("PNG");
You can call supportedImageFormats() for the full list of formats QImageReader supports.

See also:
format().


setQuality

public final void setQuality(int quality)
This is an image format specific function that sets the quality level of the image to quality. For image formats that do not support setting the quality, this value is ignored.

The value range of quality depends on the image format. For example, the "jpeg" format supports a quality range from 0 (low quality, high compression) to 100 (high quality, low compression).

See also:
quality().


setScaledClipRect

public final void setScaledClipRect(QRect rect)
Sets the scaled clip rect to rect. The scaled clip rect is the clip rect (also known as ROI, or Region Of Interest) that is applied after the image has been scaled.

See also:
scaledClipRect(), and setScaledSize().


setScaledSize

public final void setScaledSize(QSize size)
Sets the scaled size of the image to size. The scaling is performed after the initial clip rect, but before the scaled clip rect is applied. The algorithm used for scaling depends on the image format. By default (i.e., if the image format does not support scaling), QImageReader will use QImage::scale() with Qt::SmoothScaling.

See also:
scaledSize(), setClipRect(), and setScaledClipRect().


size

public final QSize size()
Returns the size of the image, without actually reading the image contents.

If the image format does not support this feature, this function returns an invalid size. Qt's built-in image handlers all support this feature, but custom image format plugins are not required to do so.

See also:
QImageIOHandler::ImageOption , QImageIOHandler::option(), and QImageIOHandler::supportsOption().


supportsAnimation

public final boolean supportsAnimation()
Returns true if the image format supports animation; otherwise, false is returned.

See also:
QMovie::supportedFormats().


supportsOption

public final boolean supportsOption(QImageIOHandler.ImageOption option)
Returns true if the reader supports option; otherwise returns false.

Different image formats support different options. Call this function to determine whether a certain option is supported by the current format. For example, the PNG format allows you to embed text into the image's metadata (see text()), and the BMP format allows you to determine the image's size without loading the whole image into memory (see size()).

        QImageReader reader = new QImageReader("classpath:/image.png");
        if (reader.supportsOption(QImageIOHandler.ImageOption.Size))
            System.err.println("Size: " + reader.size());

See also:
QImageWriter::supportsOption().


text

public final java.lang.String text(java.lang.String key)
Returns the image text associated with key.

Support for this option is implemented through QImageIOHandler::Description .

See also:
textKeys(), and QImageWriter::setText().


textKeys

public final java.util.List textKeys()
Returns the text keys for this image. You can use these keys with text() to list the image text for a certain key.

Support for this option is implemented through QImageIOHandler::Description .

See also:
text(), QImageWriter::setText(), and QImage::textKeys().


imageFormat

public static QByteArray imageFormat(QIODevice device)
If supported, this function returns the image format of the device device. Otherwise, an empty string is returned.

See also:
QImageReader::autoDetectImageFormat().


imageFormat

public static QByteArray imageFormat(java.lang.String fileName)
If supported, this function returns the image format of the file fileName. Otherwise, an empty string is returned.


supportedImageFormats

public static java.util.List supportedImageFormats()
Returns the list of image formats supported by QImageReader.

By default, Qt can read the following formats:

Format
Description
BMP Windows Bitmap
GIF Graphic Interchange Format (optional)
JPG Joint Photographic Experts Group
JPEG Joint Photographic Experts Group
MNG Multiple-image Network Graphics
PNG Portable Network Graphics
PBM Portable Bitmap
PGM Portable Graymap
PPM Portable Pixmap
TIFF Tagged Image File Format
XBM X11 Bitmap
XPM X11 Pixmap
Reading and writing SVG files is supported through Qt's SVG Module.

To configure Qt with GIF support, pass -qt-gif to the configure script or check the appropriate option in the graphical installer.

See also:
setFormat(), QImageWriter::supportedImageFormats(), and QImageIOPlugin.