QPixmap Class Reference
^{[QtGui module]}

Detailed Description

The QPixmap class is an off-screen, pixel-based paint device.

QPixmap is one of the three classes Qt provides for dealing with images, the others being QImage and QPicture. QPixmap is designed and optimized for drawing on screen; QImage is designed for I/O and for direct pixel access; QPicture provides a scalable, vectorial picture. There are static functions in QPixmap to convert between QImage and QPixmap: QPixmap::toImage() and QPixmap::fromImage(). These function can be slow on some platforms. There's also a QIcon class that stores various versions of an icon.

A common way to create a pixmap is to use the constructor that takes a file name. For example:

    label->setPixmap(QPixmap("paste.png"));

The file name can either refer to an actual file on disk or to one of the application's embedded resources. See the Resource System overview for details on how to embed images and other resource files in the application's executable.

Pixel data in a pixmap is internal and is managed by the underlying window system. Pixels can be accessed only through QPainter functions or by converting the QPixmap to a QImage.

You can easily display a QPixmap on the screen using QLabel or one of QAbstractButton's subclasses (such as QPushButton and QToolButton). QLabel has a pixmap property, whereas QAbstractButton has an icon property.

The QPixmap class uses implicit sharing, so you can pass QPixmap objects around by value.

You can retrieve the width(), height(), depth(), and size() of a pixmap. The enclosing rectangle can be determined with rect(). Pixmaps can be filled with fill(). You can create and set a mask with createHeuristicMask() and setMask(). Use selfMask() to see if the pixmap is identical to its mask.

In addition to loading a pixmap from file using load() you can also loadFromData(). You can obtain a transformed version of the pixmap using transform().

See also QBitmap, QImage, QImageReader, and Shared Classes.

Member Type Documentation

enum QPixmap::HBitmapFormat

This enum defines how the conversion between HBITMAP and QPixmap is performed.

Warning: This enum is only available on Windows.

See also fromWinHBITMAP() and toWinHBITMAP().

Member Function Documentation

QPixmap::QPixmap ()

Constructs a null pixmap.

See also isNull().

QPixmap::QPixmap ( int w, int h )

Constructs a pixmap with w width, h height.

The content of the pixmap is uninitialized.

If either w or h is zero, a null pixmap is constructed.

See also isNull().

QPixmap::QPixmap ( const QString & fileName, const char * format = 0, Qt::ImageConversionFlags flags = Qt::AutoColor )

Constructs a pixmap from the file with the given fileName. If the file does not exist or is of an unknown format, the pixmap becomes a null pixmap.

The fileName, format and flags parameters are passed on to load(). This means that the data in fileName is not compiled into the binary. If fileName contains a relative path (e.g. the filename only) the relevant file must be found relative to the runtime working directory.

The file name can either refer to an actual file on disk or to one of the application's embedded resources. See the Resource System overview for details on how to embed images and other resource files in the application's executable.

If the image needs to be modified to fit in a lower-resolution result (e.g. converting from 32-bit to 8-bit), use the flags to specify how you'd prefer this to happen.

See also Qt::ImageConversionFlags, isNull(), load(), loadFromData(), save(), and QImageReader::imageFormat().

QPixmap::QPixmap ( const char * const[] xpm )

Constructs a pixmap from xpm, which must be a valid XPM image.

Errors are silently ignored.

Note that it's possible to squeeze the XPM variable a little bit by using an unusual declaration:

    static const char * const start_xpm[]={
        "16 15 8 1",
        "a c #cec6bd",
    ....

The extra const makes the entire definition read-only, which is slightly more efficient (for example, when the code is in a shared library) and ROMable when the application is to be stored in ROM.

QPixmap::QPixmap ( const QPixmap & pixmap )

Constructs a pixmap that is a copy of pixmap.

QPixmap::QPixmap ( const QSize & size )

Constructs a pixmap of size size.

QPixmap::~QPixmap ()

Destroys the pixmap.

QPixmap QPixmap::alphaChannel () const

Returns the alpha channel of the pixmap. If the pixmap doesn't have an alpha channel a null pixmap is returned.

See also hasAlphaChannel() and setAlphaChannel().

QPixmap QPixmap::copy ( const QRect & rect = QRect() ) const

Returns a deep copy of the subpart of the pixmap that is specified by rect.

If rect is empty, the whole image is copied.

See also operator=().

QPixmap QPixmap::copy ( int x, int y, int w, int h ) const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns a deep copy of the subpart of the pixmap that is specified by the rectangle x, y, w h.

If the rectangle is empty, the whole image is copied.

QBitmap QPixmap::createHeuristicMask ( bool clipTight = true ) const

Creates and returns a heuristic mask for this pixmap. It works by selecting a color from one of the corners and then chipping away pixels of that color, starting at all the edges.

The mask may not be perfect but it should be reasonable, so you can do things such as the following:

    pm->setMask(pm->createHeuristicMask());

This function is slow because it involves transformation to a QImage, non-trivial computations and a transformation back to a QBitmap.

If clipTight is true (the default) the mask is just large enough to cover the pixels; otherwise, the mask is larger than the data pixels.

See also QImage::createHeuristicMask().

QBitmap QPixmap::createMaskFromColor ( const QColor & maskColor ) const

Creates and returns a mask for this pixmap based on maskColor.

This function is slow because it involves transformation to a QImage and a transformation back to a QBitmap.

See also createHeuristicMask().

int QPixmap::defaultDepth ()   [static]

Returns the default pixmap depth.

See also depth().

int QPixmap::depth () const

Returns the depth of the pixmap.

The pixmap depth is also called bits per pixel (bpp) or bit planes of a pixmap. A null pixmap has depth 0.

See also defaultDepth(), isNull(), and QImage::convertDepth().

void QPixmap::detach ()

This is a special-purpose function that detaches the pixmap from shared pixmap data.

A pixmap is automatically detached by Qt whenever its contents are about to change. This is done in all QPixmap member functions that modify the pixmap (fill(), convertFromImage(), load(), etc.), and in QPainter::begin() on a pixmap.

It is possible to modify a pixmap without letting Qt know. You can first obtain the system-dependent handle() and then call system-specific functions (for instance, BitBlt under Windows) that modify the pixmap contents. In such cases, you can call detach() to cut the pixmap loose from other pixmaps that share data with this one.

detach() returns immediately if there is just a single reference or if the pixmap has not been initialized yet.

void QPixmap::fill ( const QColor & fillColor = Qt::white )

Fills the pixmap with the color fillColor.

void QPixmap::fill ( const QWidget * widget, const QPoint & offset )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Fills the pixmap with the widget's background color or pixmap.

The offset point is an offset in the widget.

The point offset is a point in the widget's coordinate system. The pixmap's top-left pixel will be mapped to the point offset in the widget. This is significant if the widget has a background pixmap; otherwise the pixmap will simply be filled with the background color of the widget.

void QPixmap::fill ( const QWidget * widget, int xoff, int yoff )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Fills the pixmap with the widget's background color or pixmap. xoff, yoff is an offset in the widget.

QPixmap QPixmap::fromImage ( const QImage & image, Qt::ImageConversionFlags flags = Qt::AutoColor )   [static]

Converts the given image to a pixmap using the specified flags to control the conversion process.

The flags argument is a bitwise-OR of the Qt::ImageConversionFlags. Passing 0 for flags sets all the default options.

If the image is a monochrome image, it is converted to a 32-bit pixmap and then filled with the colors in the color table. If this is too expensive an operation, you can use QBitmap::fromImage() instead.

See also toImage(), isQBitmap(), QImage::convertDepth(), defaultDepth(), and QImage::hasAlphaBuffer().

QPixmap QPixmap::fromWinHBITMAP ( HBITMAP bitmap, HBitmapFormat format = NoAlpha )   [static]

Returns a QPixmap that is equivalent to the given bitmap which has the specified format.

See also toWinHBITMAP().

QPixmap QPixmap::grabWidget ( QWidget * widget, int x = 0, int y = 0, int w = -1, int h = -1 )   [static]

Creates a pixmap and paints widget in it.

If the widget has any children, then they are also painted in the appropriate positions.

If you specify x, y, w or h, only the rectangle you specify is painted. The defaults are 0, 0 (top-left corner) and -1,-1 (which means the entire widget).

(If w is negative, the function copies everything to the right border of the window. If h is negative, the function copies everything to the bottom of the window.)

If widget is 0, or if the rectangle defined by x, y, the modified w and the modified h does not overlap the widget->rect(), this function will return a null QPixmap.

This function actually asks widget to paint itself (and its children to paint themselves). QPixmap::grabWindow() grabs pixels off the screen, which is a bit faster and picks up exactly what's on-screen. This function works by calling paintEvent() with painter redirection turned on. If there are overlaying windows, grabWindow() will see them, but not this function.

If there is overlap, it returns a pixmap of the size you want, containing a rendering of widget. If the rectangle you ask for is a superset of widget, the areas outside widget are covered with the widget's background.

If an error occurs when trying to grab the widget, such as the size of the widget being too large to fit in memory, an isNull() pixmap is returned.

Warning: Do not call this function from with a paintEvent().

See also grabWindow() and QWidget::paintEvent().

QPixmap QPixmap::grabWidget ( QWidget * widget, const QRect & rect )   [static]

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Creates a pixmap and paints widget in it. If the widget has any children, then they are also painted in the appropriate positions.

If rect is a valid rectangle, only the rectangle you specify is painted.

Warning: Do not call this function from with a paintEvent().

grabWidget(), QRect::isValid()

QPixmap QPixmap::grabWindow ( WId window, int x = 0, int y = 0, int w = -1, int h = -1 )   [static]

Grabs the contents of the window window and makes a pixmap out of it. Returns the pixmap.

The arguments (x, y) specify the offset in the window, whereas (w, h) specify the width and height of the area to be copied.

If w is negative, the function copies everything to the right border of the window. If h is negative, the function copies everything to the bottom of the window.

Note that grabWindow() grabs pixels from the screen, not from the window. If there is another window partially or entirely over the one you grab, you get pixels from the overlying window, too.

Note also that the mouse cursor is generally not grabbed.

The reason we use a window identifier and not a QWidget is to enable grabbing of windows that are not part of the application, window system frames, and so on.

Warning: Grabbing an area outside the screen is not safe in general. This depends on the underlying window system.

Warning: X11 only: If window is not the same depth as the root window and another window partially or entirely obscures the one you grab, you will not get pixels from the overlying window. The contests of the obscured areas in the pixmap are undefined and uninitialized.

See also grabWidget().

bool QPixmap::hasAlpha () const

Returns true if this pixmap has an alpha channel or a mask.

See also hasAlphaChannel() and mask().

bool QPixmap::hasAlphaChannel () const

Returns true if the pixmap has an alpha channel; otherwise it returns false.

See also hasAlpha() and mask().

int QPixmap::height () const

Returns the height of the pixmap.

See also width(), size(), and rect().

bool QPixmap::isNull () const

Returns true if this is a null pixmap; otherwise returns false.

A null pixmap has zero width, zero height and no contents. You cannot draw in a null pixmap.

Resizing an existing pixmap to (0, 0) makes a pixmap into a null pixmap.

bool QPixmap::isQBitmap () const

Returns true if this is a QBitmap; otherwise returns false.

bool QPixmap::load ( const QString & fileName, const char * format = 0, Qt::ImageConversionFlags flags = Qt::AutoColor )

Loads a pixmap from the file fileName at runtime. Returns true if successful; otherwise returns false.

If format is specified, the loader attempts to read the pixmap using the specified format. If format is not specified (default), the loader reads a few bytes from the header to guess the file's format.

If the data needs to be modified to fit in a lower-resolution result (e.g. converting from 32-bit to 8-bit), use the flags to specify how you'd prefer this to happen.

The QImageReader documentation lists the supported image formats and explains how to add extra formats.

The file name can either refer to an actual file on disk or to one of the application's embedded resources. See the Resource System overview for details on how to embed images and other resource files in the application's executable.

QImageReader

See also loadFromData(), save(), QImageReader::imageFormat(), QImage::load(), and fromImage().

bool QPixmap::loadFromData ( const uchar * buf, uint len, const char * format = 0, Qt::ImageConversionFlags flags = Qt::AutoColor )

Loads a pixmap from the binary data in buf (len bytes). Returns true if successful; otherwise returns false.

If format is specified, the loader attempts to read the pixmap using the specified format. If format is not specified (default), the loader reads a few bytes from the header to guess the file's format.

If the data needs to be modified to fit in a lower-resolution result (e.g. converting from 32-bit to 8-bit), use the flags to specify how you'd prefer this to happen.

The QImageReader documentation lists the supported image formats and explains how to add extra formats.

See also load(), save(), QImageReader::imageFormat(), QImage::loadFromData(), fromImage(), and QImageReader.

bool QPixmap::loadFromData ( const QByteArray & buf, const char * format = 0, Qt::ImageConversionFlags flags = Qt::AutoColor )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Loads a pixmap from the binary data buf.

If format is specified, the loader attempts to read the pixmap using the specified format. If format is not specified (default), the loader reads a few bytes from the header to guess the file's format.

If the data needs to be modified to fit in a lower-resolution result (e.g. converting from 32-bit to 8-bit), use the flags to specify how you'd prefer this to happen.

QBitmap QPixmap::mask () const

Returns the mask, or a null bitmap if no mask has been set.

See also setMask(), QBitmap, and hasAlpha().

QRect QPixmap::rect () const

Returns the enclosing rectangle (0,0,width(),height()) of the pixmap.

See also width(), height(), and size().

bool QPixmap::save ( const QString & fileName, const char * format, int quality = -1 ) const

Saves the pixmap to the file fileName using the image file format format and a quality factor quality. quality must be in the range [0,100] or -1. Specify 0 to obtain small compressed files, 100 for large uncompressed files, and -1 to use the default settings. Returns true if successful; otherwise returns false.

See also load(), loadFromData(), QImageReader::imageFormat(), QImage::save(), and QImageReader.

bool QPixmap::save ( QIODevice * device, const char * format, int quality = -1 ) const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

This function writes a QPixmap to the QIODevice, device using the image file format format. This can be used, for example, to save a pixmap directly into a QByteArray:

            QPixmap pixmap;
            QByteArray bytes;
            QBuffer buffer(&bytes);
            buffer.open(QIODevice::WriteOnly);
            pixmap.save(&buffer, "PNG"); // writes pixmap into bytes in PNG format

The quality parameter is a quality factor quality. quality must be in the range [0,100] or -1. Specify 0 to obtain small compressed files, 100 for large uncompressed files, and -1 to use the default settings.

QPixmap QPixmap::scaled ( int w, int h, Qt::AspectRatioMode aspectRatioMode = Qt::IgnoreAspectRatio, Qt::TransformationMode transformMode = Qt::FastTransformation ) const

Returns a copy of the pixmap scaled to a rectangle of width w and height h according to aspectRatioMode and transformMode.

• If aspectRatioMode is Qt::IgnoreAspectRatio, the pixmap is scaled to (w, h).
• If aspectRatioMode is Qt::KeepAspectRatio, the pixmap is scaled to a rectangle as large as possible inside (w, h), preserving the aspect ratio.
• If aspectRatioMode is Qt::KeepAspectRatioByExpanding, the pixmap is scaled to a rectangle as small as possible outside (w, h), preserving the aspect ratio.

If either the width w or the height h is zero or negative, this function returns a null pixmap.

See also scaledToWidth(), scaledToHeight(), and transformed().

QPixmap QPixmap::scaled ( const QSize & size, Qt::AspectRatioMode aspectMode = Qt::IgnoreAspectRatio, Qt::TransformationMode transformMode = Qt::FastTransformation ) const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Scales the pixmap to the given size, using the aspect ratio and transformation modes specified by aspectMode and transformMode.

QPixmap QPixmap::scaledToHeight ( int h, Qt::TransformationMode mode = Qt::FastTransformation ) const

Returns a scaled copy of the pixmap using a transformation specified by mode. The returned pixmap has a height of h pixels. This function automatically calculates the width of the pixmap so that the ratio of the pixmap is preserved.

If h is 0 or negative a null pixmap is returned.

See also scaled(), scaledToWidth(), and transformed().

QPixmap QPixmap::scaledToWidth ( int w, Qt::TransformationMode mode = Qt::FastTransformation ) const

Returns a scaled copy of the pixmap using a transformation specified by mode. The returned pixmap has a width of w pixels. This function automatically calculates the height of the pixmap so that the ratio of the pixmap is preserved.

If w is 0 or negative a null pixmap is returned.

See also scaled(), scaledToHeight(), and transformed().

int QPixmap::serialNumber () const

Returns a number that uniquely identifies the contents of this QPixmap object. This means that multiple QPixmap objects can have the same serial number as long as they refer to the same contents.

A null pixmap always have a serial number of 0.

An example of where this is useful is for caching QPixmaps.

See also QPixmapCache.

void QPixmap::setAlphaChannel ( const QPixmap & alpha )

Sets the alpha channel of this pixmap to alpha. If the pixmap already contains an alpha channel, it is merged with alpha.

See also alphaChannel().

void QPixmap::setMask ( const QBitmap & newmask )

Sets a mask bitmap.

The newmask bitmap defines the clip mask for this pixmap. Every pixel in newmask corresponds to a pixel in this pixmap. Pixel value 1 means opaque and pixel value 0 means transparent. The mask must have the same size as this pixmap.

Warning: Setting the mask on a pixmap will cause any alpha channel data to be cleared. For example:

            QPixmap alpha("image-with-alpha.png");
            QPixmap alphacopy = alpha;
            alphacopy.setMask(*alphacopy.mask());

Now, alpha and alphacopy are visually different.

Setting a null mask resets the mask.

See also mask(), createHeuristicMask(), and QBitmap.

QSize QPixmap::size () const

Returns the size of the pixmap.

See also width(), height(), and rect().

QImage QPixmap::toImage () const

Converts the pixmap to a QImage. Returns a null image if it fails.

If the pixmap has 1-bit depth, the returned image will also be 1 bit deep. If the pixmap has 2- to 8-bit depth, the returned image has 8-bit depth. If the pixmap has greater than 8-bit depth, the returned image has 32-bit depth.

Note that for the moment, alpha masks on monochrome images are ignored.

See also convertFromImage().

HBITMAP QPixmap::toWinHBITMAP ( HBitmapFormat format = NoAlpha ) const

Creates a HBITMAP equivalent to the QPixmap, based on the given format, and returns the HBITMAP handle.

It is the caller's responsibility to free the HBITMAP data after use.

Warning: This function is only available on Windows.

See also fromWinHBITMAP().

QPixmap QPixmap::transformed ( const QMatrix & matrix, Qt::TransformationMode mode = Qt::FastTransformation ) const

Returns a copy of the pixmap that is transformed using matrix. The original pixmap is not changed.

The transformation matrix is internally adjusted to compensate for unwanted translation, i.e. transformed() returns the smallest image that contains all the transformed points of the original image.

mode specifies whether the transformation should be smooth or not.

This function is slow because it involves transformation to a QImage, non-trivial computations and a transformation back to a QPixmap.

See also trueMatrix(), QMatrix, QPainter::setWorldMatrix(), and QImage::transformed().

QMatrix QPixmap::trueMatrix ( const QMatrix & m, int w, int h )   [static]

Returns the actual matrix used for transforming a pixmap with w width and h height and matrix m.

When transforming a pixmap with transform(), the transformation matrix is internally adjusted to compensate for unwanted translation, i.e. transform() returns the smallest pixmap containing all transformed points of the original pixmap.

This function returns the modified matrix, which maps points correctly from the original pixmap into the new pixmap.

See also transformed() and QMatrix.

int QPixmap::width () const

Returns the width of the pixmap.

See also height(), size(), and rect().

const QX11Info & QPixmap::x11Info () const

Returns a pointer to a QX11Info object. This pointer is owned by QPixmap and should not be deleted.

Qt::HANDLE QPixmap::x11PictureHandle () const

Returns the X11 Picture handle of the pixmap for XRender support. Use of this function is not portable. This function will return 0 if XRender support is not compiled into Qt, if the XRender extension is not supported on the X11 display, or if the handle could not be created.

QPixmap::operator QVariant () const

Returns the pixmap as a QVariant

bool QPixmap::operator! () const

Returns true if this is a null pixmap; otherwise returns false.

See also isNull().

QPixmap & QPixmap::operator= ( const QPixmap & pixmap )

Assigns the pixmap pixmap to this pixmap and returns a reference to this pixmap.

Related Non-Members

QDataStream & operator>> ( QDataStream & s, QPixmap & pixmap )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Reads a pixmap from the stream s into the pixmap pixmap.

Format of the QDataStream operators

See also QPixmap::load().