QPixmap Class Reference

Detailed Description

QPixmap is one of the two classes Qt provides for dealing with images; the other is QImage. QPixmap is designed and optimized for drawing; QImage is designed and optimized for I/O and for direct pixel access/manipulation. There are (slow) functions to convert between QImage and QPixmap: convertToImage() and convertFromImage().

One common use of the QPixmap class is to enable smooth updating of widgets. Whenever something complex needs to be drawn, you can use a pixmap to obtain flicker-free drawing, like this:

1. Create a pixmap with the same size as the widget.
2. Fill the pixmap with the widget background color.
3. Paint the pixmap.
4. bitBlt() the pixmap contents onto the widget.

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

You can easily display a QPixmap on the screen using QLabel::setPixmap(). For example, all the QButton subclasses support pixmap use.

The QPixmap class uses copy-on-write, so it is practical to pass QPixmap objects by value.

You can retrieve the width(), height(), depth() and size() of a pixmap. The enclosing rectangle is given by rect(). Pixmaps can be filled with fill() and resized with resize(). 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 control optimization with setOptimization() and obtain a transformed version of the pixmap using xForm()

Note regarding Windows 95 and 98: on Windows 9x the system crashes if you create more than about 1000 pixmaps, independent of the size of the pixmaps or installed RAM. Windows NT and 2000 do not have this limitation.

Qt tries to work around the resource limitation. If you set the pixmap optimization to QPixmap::MemoryOptim and the width of your pixmap is less than or equal to 128 pixels, Qt stores the pixmap in a way that is very memory-efficient when there are many pixmaps.

If your application uses dozens or hundreds of pixmaps (for example on tool bar buttons and in popup menus), and you plan to run it on Windows 95 or Windows 98, we recommend using code like this:

        QPixmap::setDefaultOptimization( QPixmap::MemoryOptim );
        while ( ... ) {
            // load tool bar pixmaps etc.
            QPixmap *pixmap = new QPixmap(fileName);
        }
        QPixmap::setDefaultOptimization( QPixmap::NormalOptim );
    

See also QBitmap, QImage, QImageIO, Shared Classes, Graphics Classes, Image Processing Classes and Implicitly and Explicitly Shared Classes.

Member Type Documentation

QPixmap::ColorMode

This enum type defines the color modes that exist for converting QImage objects to QPixmap.

• QPixmap::Auto - Select Color or Mono on a case-by-case basis.
• QPixmap::Color - Always create colored pixmaps.
• QPixmap::Mono - Always create bitmaps.

QPixmap::Optimization

QPixmap has the choice of optimizing for speed or memory in a few places; the best choice varies from pixmap to pixmap but can generally be derived heuristically. This enum type defines a number of optimization modes that you can set for any pixmap to tweak the speed/memory tradeoffs:

• QPixmap::DefaultOptim - Whatever QPixmap::defaultOptimization() returns. A pixmap with this optimization will have whatever the current default optimization is. If the default optimization is changed using setDefaultOptimization(), then this will not effect any pixmaps that have already been created.
• QPixmap::NoOptim - No optimization (currently the same as MemoryOptim).
• QPixmap::MemoryOptim - Optimize for minimal memory use.
• QPixmap::NormalOptim - Optimize for typical usage. Often uses more memory than MemoryOptim, and is often faster.
• QPixmap::BestOptim - Optimize for pixmaps that are drawn very often and where performance is critical. Generally uses more memory than NormalOptim and may provide a little more speed.

We recommend using DefaultOptim.

Member Function Documentation

QPixmap::QPixmap ()

See also isNull().

QPixmap::QPixmap ( const QImage & image )

See also convertFromImage().

QPixmap::QPixmap ( int w, int h, int depth = -1, Optimization optimization = DefaultOptim )

The contents of the pixmap is uninitialized.

The depth can be either 1 (monochrome) or the depth of the current video mode. If depth is negative, then the hardware depth of the current video mode will be used.

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

See also isNull() and QPixmap::Optimization.

QPixmap::QPixmap ( const QSize & size, int depth = -1, Optimization optimization = DefaultOptim )

Constructs a pixmap of size size, depth bits per pixel, optimized in accordance with the optimization value.

QPixmap::QPixmap ( const QString & fileName, const char * format = 0, ColorMode mode = Auto )

The fileName, format and mode 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.

See also QPixmap::ColorMode, isNull(), load(), loadFromData(), save() and imageFormat().

QPixmap::QPixmap ( const QString & fileName, const char * format, int conversion_flags )

The fileName, format and conversion_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.

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 conversion_flags to specify how you'd prefer this to happen.

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

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

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.

In order to use that sort of declaration you must cast the variable back to const char ** when you create the QPixmap.

QPixmap::QPixmap ( const QByteArray & img_data )

See also loadFromData().

QPixmap::QPixmap ( const QPixmap & pixmap )

QPixmap::QPixmap ( int w, int h, const uchar * bits, bool isXbitmap ) [protected]

QPixmap::~QPixmap ()

bool QPixmap::convertFromImage ( const QImage & img, int conversion_flags )

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

Note that even though a QPixmap with depth 1 behaves much like a QBitmap, isQBitmap() returns FALSE.

If a pixmap with depth 1 is painted with color0 and color1 and converted to an image, the pixels painted with color0 will produce pixel index 0 in the image and those painted with color1 will produce pixel index 1.

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

Examples: canvas/canvas.cpp, qtimage/qtimage.cpp and themes/wood.cpp.

bool QPixmap::convertFromImage ( const QImage & image, ColorMode mode = Auto )

Converts image and sets this pixmap using color mode mode. Returns TRUE if successful; otherwise returns FALSE.

See also QPixmap::ColorMode.

QImage QPixmap::convertToImage () const

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().

Example: qmag/qmag.cpp.

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

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 mask is just large enough to cover the pixels; otherwise, the mask is larger than the data pixels.

See also QImage::createHeuristicMask().

int QPixmap::defaultDepth () [static]

See also depth().

Optimization QPixmap::defaultOptimization () [static]

See also setDefaultOptimization(), setOptimization() and optimization().

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 () [virtual]

A pixmap is automatically detached by Qt whenever its contents is about to change. This is done in all QPixmap member functions that modify the pixmap (fill(), resize(), convertFromImage(), load(), etc.), in bitBlt() for the destination pixmap 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 )

Examples: chart/setdataform.cpp, desktop/desktop.cpp, grapher/grapher.cpp, hello/hello.cpp, t10/cannon.cpp, themes/metal.cpp and xform/xform.cpp.

void QPixmap::fill ( const QWidget * widget, int xofs, int yofs )

Fills the pixmap with the widget's background color or pixmap. If the background is empty, nothing is done. xofs, yofs is an offset in the widget.

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

Fills the pixmap with the widget's background color or pixmap. If the background is empty, nothing is done.

The ofs point is an offset in the widget.

The point ofs is a point in the widget's coordinate system. The pixmap's top-left pixel will be mapped to the point ofs 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.

Example:

    void CuteWidget::paintEvent( QPaintEvent *e )
    {
        QRect ur = e->rect();            // rectangle to update
        QPixmap pix( ur.size() );        // Pixmap for double-buffering
        pix.fill( this, ur.topLeft() );  // fill with widget background

        QPainter p( &pix );
        p.translate( -ur.x(), -ur.y() ); // use widget coordinate system
                                         // when drawing on pixmap
        //    ... draw on pixmap ...

        p.end();

        bitBlt( this, ur.topLeft(), &pix );
    }
    

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

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.

See also grabWindow(), QPainter::redirect() and QWidget::paintEvent().

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

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.

See also grabWidget().

Example: qmag/qmag.cpp.

int QPixmap::height () const

Returns the height of the pixmap.

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

Examples: desktop/desktop.cpp, movies/main.cpp, qtimage/qtimage.cpp, scribble/scribble.cpp, scrollview/scrollview.cpp, t10/cannon.cpp and xform/xform.cpp.

const char * QPixmap::imageFormat ( const QString & fileName ) [static]

The QImageIO documentation lists the supported image formats.

See also load() and save().

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 or bitBlt() anything to it.

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

See also resize().

Examples: movies/main.cpp, qdir/qdir.cpp, qmag/qmag.cpp and scrollview/scrollview.cpp.

bool QPixmap::isQBitmap () const

Returns TRUE if this is a QBitmap; otherwise returns FALSE.

bool QPixmap::load ( const QString & fileName, const char * format, int conversion_flags )

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.

See the convertFromImage() documentation for a description of the conversion_flags argument.

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

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

Examples: picture/picture.cpp, scrollview/scrollview.cpp and xform/xform.cpp.

bool QPixmap::load ( const QString & fileName, const char * format = 0, ColorMode mode = Auto )

Loads a pixmap from the file fileName at runtime.

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.

The mode is used to specify the color mode of the pixmap.

See also QPixmap::ColorMode.

bool QPixmap::loadFromData ( const uchar * buf, uint len, const char * format, int conversion_flags )

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.

See the convertFromImage() documentation for a description of the conversion_flags argument.

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

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

bool QPixmap::loadFromData ( const uchar * buf, uint len, const char * format = 0, ColorMode mode = Auto )

Loads a pixmap from the binary data in buf (len bytes) using color mode mode. 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.

See also QPixmap::ColorMode.

bool QPixmap::loadFromData ( const QByteArray & buf, const char * format = 0, int conversion_flags = 0 )

const QBitmap * QPixmap::mask () const

Returns the mask bitmap, or 0 if no mask has been set.

See also setMask() and QBitmap.

int QPixmap::metric ( int m ) const [virtual protected]

Use the QPaintDeviceMetrics class instead.

m is the metric to get.

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

QPixmap & QPixmap::operator= ( const QImage & image )

Converts the image image to a pixmap that is assigned to this pixmap. Returns a reference to the pixmap.

See also convertFromImage().

Optimization QPixmap::optimization () const

Returns the optimization setting for this pixmap.

The default optimization setting is QPixmap::NormalOptim. You can change this setting in two ways:

• Call setDefaultOptimization() to set the default optimization for all new pixmaps.
• Call setOptimization() to set the optimization for individual pixmaps.

See also setOptimization(), setDefaultOptimization() and defaultOptimization().

QRect QPixmap::rect () const

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

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

Example: xform/xform.cpp.

void QPixmap::resize ( int w, int h )

If both w and h are greater than 0, a valid pixmap is created. New pixels will be uninitialized (random) if the pixmap is expanded.

Examples: desktop/desktop.cpp and grapher/grapher.cpp.

void QPixmap::resize ( const QSize & size )

Resizes the pixmap to size size.

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

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

Example: qmag/qmag.cpp.

bool QPixmap::selfMask () const

Returns TRUE if the pixmap's mask is identical to the pixmap itself; otherwise returns FALSE.

See also mask().

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.

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

See also QPixmapCache.

void QPixmap::setDefaultOptimization ( Optimization optimization ) [static]

All new pixmaps that are created will use this default optimization. You may also set optimization for individual pixmaps using the setOptimization() function.

The initial default optimization setting is QPixmap::Normal.

See also defaultOptimization(), setOptimization() and optimization().

void QPixmap::setMask ( const QBitmap & newmask )

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() );
    

Setting a null mask resets the mask.

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

void QPixmap::setOptimization ( Optimization optimization )

The optimization setting affects pixmap operations, in particular drawing of transparent pixmaps (bitBlt() a pixmap with a mask set) and pixmap transformations (the xForm() function).

Pixmap optimization involves keeping intermediate results in a cache buffer and using the cache to speed up bitBlt() and xForm(). The cost is more memory consumption, up to twice as much as an unoptimized pixmap.

Use the setDefaultOptimization() to change the default optimization for all new pixmaps.

See also optimization(), setDefaultOptimization() and defaultOptimization().

Example: desktop/desktop.cpp.

QSize QPixmap::size () const

Returns the size of the pixmap.

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

Examples: movies/main.cpp and qtimage/qtimage.cpp.

QWMatrix QPixmap::trueMatrix ( const QWMatrix & matrix, int w, int h ) [static]

When transforming a pixmap with xForm(), the transformation matrix is internally adjusted to compensate for unwanted translation, i.e. xForm() 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 xForm() and QWMatrix.

int QPixmap::width () const

Returns the width of the pixmap.

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

Examples: desktop/desktop.cpp, movies/main.cpp, qtimage/qtimage.cpp, scribble/scribble.cpp, scrollview/scrollview.cpp and xform/xform.cpp.

QPixmap QPixmap::xForm ( const QWMatrix & matrix ) const

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

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

See also trueMatrix(), QWMatrix, QPainter::setWorldMatrix() and QImage::xForm().

Examples: desktop/desktop.cpp, fileiconview/qfileiconview.cpp, movies/main.cpp, qmag/qmag.cpp, qtimage/qtimage.cpp and xform/xform.cpp.

Related Functions

QDataStream & operator<< ( QDataStream & s, const QPixmap & pixmap )

Writes the pixmap pixmap to the stream s as a PNG image.

See also QPixmap::save() and Format of the QDataStream operators.

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

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

See also QPixmap::load() and Format of the QDataStream operators.

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