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com.trolltech.qt.gui
Class QImageReader

java.lang.Object
  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.

See Also:
QImageWriter, QImageIOHandler, 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.Signal0, QSignalEmitter.Signal1<A>, QSignalEmitter.Signal2<A,B>, QSignalEmitter.Signal3<A,B,C>, QSignalEmitter.Signal4<A,B,C,D>, QSignalEmitter.Signal5<A,B,C,D,E>, QSignalEmitter.Signal6<A,B,C,D,E,F>, QSignalEmitter.Signal7<A,B,C,D,E,F,G>, QSignalEmitter.Signal8<A,B,C,D,E,F,G,H>, QSignalEmitter.Signal9<A,B,C,D,E,F,G,H,I>
 
Constructor Summary
QImageReader()
          Constructs an empty QImageReader object.
QImageReader(QIODevice device)
          Equivalent to QImageReader(device, QByteArray()).
QImageReader(QIODevice device, QByteArray format)
          Constructs a QImageReader object with the device device and the image format format.
QImageReader(java.lang.String fileName)
          Equivalent to QImageReader(fileName, QByteArray()).
QImageReader(java.lang.String fileName, QByteArray format)
          Constructs a QImageReader object with the file name fileName and the image format format.
 
Method Summary
 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.e., the image format is supported, and the device seems to contain valid data); otherwise returns false.
 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.
static QImageReader fromNativePointer(QNativePointer nativePointer)
          This function returns the QImageReader instance pointed to by nativePointer
 int imageCount()
          For image formats that support animation, this function returns the total number of images in the animation.
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 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<QByteArray> 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<java.lang.String> textKeys()
          Returns the text keys for this image.
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class java.lang.Object
clone, equals, 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(java.lang.String fileName)

Equivalent to QImageReader(fileName, QByteArray()).


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

QImageReader

public QImageReader()

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


QImageReader

public QImageReader(QIODevice device)

Equivalent to QImageReader(device, QByteArray()).


QImageReader

public QImageReader(QIODevice device,
                    QByteArray format)

Constructs a QImageReader object with the device device and the image format format.

Method Detail

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, read

canRead

public final boolean canRead()

Returns true if an image can be read for the device (i.e., 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, 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, 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, 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, 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, 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("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, 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, QImageIOHandler::imageCount

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, 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, 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, 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, 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, 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

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, 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, 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, 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, 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;
    reader.setFormat("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, 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, 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, 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(":/image.png");
    if (reader.supportsOption(QImageIOHandler::Size))
        qDebug() << "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, QImageWriter::setText

textKeys

public final java.util.List<java.lang.String> 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, QImage::textKeys

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.


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.


supportedImageFormats

public static java.util.List<QByteArray> supportedImageFormats()

Returns the list of image formats supported by QImageReader.

By default, Qt can read the following formats:

FormatDescription
BMPWindows Bitmap
GIFGraphic Interchange Format (optional)
JPGJoint Photographic Experts Group
JPEGJoint Photographic Experts Group
MNGMultiple-image Network Graphics
PNGPortable Network Graphics
PBMPortable Bitmap
PGMPortable Graymap
PPMPortable Pixmap
TIFFTagged Image File Format
XBMX11 Bitmap
XPMX11 Pixmap

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, QImageIOPlugin

fromNativePointer

public static QImageReader fromNativePointer(QNativePointer nativePointer)
This function returns the QImageReader instance pointed to by nativePointer

Parameters:
nativePointer - the QNativePointer of which object should be returned.

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