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java.lang.Objectcom.trolltech.qt.QSignalEmitter
com.trolltech.qt.QtJambiObject
com.trolltech.qt.gui.QImageReader
public class QImageReader
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.
Nested Class Summary | |
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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 |
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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 | |
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QImageReader()
Constructs an empty QImageReader object. |
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QImageReader(QIODevice device)
Equivalent to QImageReader(device, QByteArray()). |
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QImageReader(QIODevice device,
QByteArray format)
Constructs a QImageReader object with the device device and the image format format. |
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QImageReader(java.lang.String fileName)
Equivalent to QImageReader(fileName, QByteArray()). |
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QImageReader(java.lang.String fileName,
QByteArray format)
Constructs a QImageReader object with the file name fileName and the image format format. |
Method Summary | |
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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 |
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dispose, disposed, finalize, reassignNativeResources, tr, tr, tr |
Methods inherited from class com.trolltech.qt.QSignalEmitter |
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blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread |
Methods inherited from class java.lang.Object |
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clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Methods inherited from interface com.trolltech.qt.QtJambiInterface |
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disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership |
Constructor Detail |
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public QImageReader(java.lang.String fileName)
Equivalent to QImageReader(fileName, QByteArray()).
public QImageReader(java.lang.String fileName, QByteArray format)
Constructs a QImageReader object with the file name fileName and the image format format.
public QImageReader()
Constructs an empty QImageReader object. Before reading an image, call setDevice or setFileName.
public QImageReader(QIODevice device)
Equivalent to QImageReader(device, QByteArray()).
public QImageReader(QIODevice device, QByteArray format)
Constructs a QImageReader object with the device device and the image format format.
Method Detail |
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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.
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.
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.
public final int currentImageNumber()
For image formats that support animation, this function returns the sequence number of the current frame. Otherwise, -1 is returned.
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.
public final QIODevice device()
Returns the device currently assigned to QImageReader, or 0 if no device has been assigned.
public final QImageReader.ImageReaderError error()
Returns the type of error that occurred last.
public final java.lang.String errorString()
Returns a human readable description of the last error that occurred.
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.
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.
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.
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.
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.
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.
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.
public final int quality()
Returns the quality level of the image.
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.
public final QRect scaledClipRect()
Returns the scaled clip rect of the image.
public final QSize scaledSize()
Returns the scaled size of the image.
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.
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.
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.
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.
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.
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).
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.
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.
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.
public final boolean supportsAnimation()
Returns true if the image format supports animation; otherwise, false is returned.
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();
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.
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.
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.
public static QByteArray imageFormat(QIODevice device)
If supported, this function returns the image format of the device device. Otherwise, an empty string is returned.
public static java.util.List<QByteArray> supportedImageFormats()
Returns the list of image formats supported by QImageReader.
By default, Qt can read the following formats:
Format | Description |
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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 |
To configure Qt with GIF support, pass -qt-gif to the configure script or check the appropriate option in the graphical installer.
public static QImageReader fromNativePointer(QNativePointer nativePointer)
nativePointer
- the QNativePointer of which object should be returned.
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