QPixmap Class Reference
The QPixmap class is an off-screen pixel-based paint device.
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#include <qpixmap.h>
Inherits QPaintDevice and Qt.
Inherited by QBitmap and QCanvasPixmap.
List of all member functions.
Public Members
Static Public Members
-
QPixmapÂ
grabWindow ( WId, int x=0, int y=0, int w=-1, int h=-1 )Â
QPixmapÂ
grabWidget ( QWidget * widget, int x=0, int y=0, int w=-1, int h=-1 )Â
QWMatrixÂ
trueMatrix ( const QWMatrix &, int w, int h )Â
const char*Â
imageFormat ( const QString & fileName )Â
-
-
Protected Members
QPixmap ( int w, int h, const uchar * data, bool isXbitmap )Â
virtual intÂ
metric ( int ) const
Related Functions
(Note that these are not member functions.)
- QDataStream & operator>> (QDataStream & s, QPixmap & pixmap)
- QDataStream & operator<< (QDataStream & s, const QPixmap & pixmap)
Detailed Description
The QPixmap class is an off-screen pixel-based paint device.
It is one of the two classes Qt provides for dealing with images,
the other being 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:
- Create a pixmap with the same size as the widget.
- Fill the pixmap with the widget background color.
- Paint the pixmap.
- bitBlt() the pixmap contents onto the widget.
Pixel data in a pixmap is internal and managed by the underlying
window system. Pixels can only be accessed through QPainter
functions, through bitBlt(), and by converting the QPixmap to a
QImage.
You can display a QPixmap on the screen easily using
e.g. QLabel::setPixmap(), and all the QButton subclasses support
pixmap use.
The QPixmap class uses lazy copying, so it is practical to pass pass
QPixmap objects as arguments.
Note about Windows 95 and 98: On Windows 9x, the system crashes if
you create more than approximately 1000 pixmaps, independent of the
size of the pixmaps or installed RAM. Windows NT does 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 which is very memory-efficient when there are many pixmaps.
If your application uses dozens or hundreds of pixmaps, e.g. on tool
bar buttons, in popup menus, and you plan to run it on Windows 95 or
Windows 98, then 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 and Shared Classes
Examples:
qtimage/qtimage.cpp
movies/main.cpp
picture/picture.cpp
xform/xform.cpp
menu/menu.cpp
qmag/qmag.cpp
desktop/desktop.cpp
scrollview/scrollview.cpp
Member Type Documentation
This enum type defines the color modes that exist for converting
QImage objects to QPixmap. The current values are:
-
Auto - select Color or Mono on a case-by-case basis.
-
Color - always create colored pixmaps.
-
Mono - always create bitmaps.
QPixmap has the choice of optimizing for speed or memory in a few
places, and the best choice varies from pixmap to pixmap, but can
generally be derived heuristically. This enum type defines a number
of optimization modes you can set for any pixmap, to tweak the
speed/memory tradeoffs:
-
DefaultOptim - whatever QPixmap::defaultOptimization()
returns. A pixmap with this optimization mode set always has the
default optimization type, even if the default is changed with
setDefaultOptimization().
-
NoOptim - no optimization (currently the same as MemoryOptim).
-
MemoryOptim - optimize for minimal memory use.
-
NormalOptim - optimize for typical usage. Often uses more
memory than MemoryOptim, and often faster.
-
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 better speed.
We recommend sticking with DefaultOptim
Member Function Documentation
QPixmap::QPixmap ()
Constructs a null pixmap.
See also isNull().
QPixmap::QPixmap ( const QByteArray & img_data )
Constructs a pixmaps by loading from img_data.
The data can be in any image format supported by Qt.
See also loadFromData().
QPixmap::QPixmap ( const QString & fileName, const char * format, int conversion_flags )
Constructs a pixmap from the file fileName. If the file does not
exist, or is of an unknown format, the pixmap becomes a null pixmap.
The parameters are passed on to load().
See also isNull(), load(), loadFromData(), save() and imageFormat().
QPixmap::QPixmap ( const QString & fileName, const char * format=0, ColorMode mode=Auto )
Constructs a pixmap from the file fileName. If the file does not
exist, or is of an unknown format, the pixmap becomes a null pixmap.
The parameters are passed on to load().
See also isNull(), load(), loadFromData(), save() and imageFormat().
QPixmap::QPixmap ( const QPixmap & pixmap )
Constructs a pixmap which is a copy of pixmap.
QPixmap::QPixmap ( const char * xpm[] )
Constructs a pixmap from xpm, which must be a valid XPM image.
Error 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 e.g. 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 ( int w, int h, const uchar * bits, bool isXbitmap ) [protected]
Constructs a monochrome pixmap which is initialized with the data in bits.
This constructor is protected and used by the QBitmap class.
QPixmap::QPixmap ( int w, int h, int depth = -1, Optimization optimization = DefaultOptim )
Constructs a pixmap with w width, h height and of depth bits per
pixels.
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 width or height is zero, a null pixmap is constructed.
See also isNull().
QPixmap::QPixmap ( const QSize & size, int depth = -1, Optimization optimization = DefaultOptim )
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
QPixmap::~QPixmap ()
Destructs the pixmap.
bool QPixmap::convertFromImage ( const QImage & img, int conversion_flags )
Converts an image and sets this pixmap. Returns TRUE if successful.
The conversion_flags argument is a bitwise-OR from the following choices.
The options marked (default) are the choice if no other choice from the
list is included (they are zero):
- Color/Mono preference (ignored for QBitmap)
-
-
AutoColor (default) - If the image has depth 1 and contains only
black and white pixels, then the pixmap becomes monochrome.
-
ColorOnly - The pixmap is dithered/converted to the
native display depth.
-
MonoOnly - The pixmap becomes monochrome. If necessary,
it is dithered using the chosen dithering algorithm.
- Dithering mode preference, for RGB channels
-
-
DiffuseDither (default) - a high quality dither
-
OrderedDither - a faster more ordered dither
-
ThresholdDither - no dithering, closest color is used
- Dithering mode preference, for alpha channel
-
-
DiffuseAlphaDither - a high quality dither
-
OrderedAlphaDither - a faster more ordered dither
-
ThresholdAlphaDither (default) - no dithering
- Color matching versus dithering preference
-
-
PreferDither - always dither 32-bit images when
the image
is being converted to 8-bits.
This is the default when converting to a pixmap.
-
AvoidDither - only dither 32-bit images if
the image
has more than 256 colors and it
is being converted to 8-bits.
This is the default when an image is converted
for the purpose of saving to a file.
Passing 0 for conversion_flags gives 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().
Bugs and limitations:
- Does not support 2 or 4 bit display hardware.
Examples:
qtimage/qtimage.cpp
bool QPixmap::convertFromImage ( const QImage & image, ColorMode mode=Auto )
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
QImage QPixmap::convertToImage () const
Converts the pixmap to an image. Returns a null image if the operation
failed.
If the pixmap has 1 bit depth, the returned image will also be 1
bits deep. If the pixmap has 2-8 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.
See also convertFromImage().
Bugs and limitations:
- Does not support 2 or 4 bit display hardware.
- Alpha masks on monochrome images are ignored.
Examples:
qmag/qmag.cpp
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, then chipping away pixels of
that color, starting at all the edges.
The mask may not be perfect but should be reasonable, so you can do
things like:
pm->setMask( pm->createHeuristicMask() );
This function is slow because it involves transformation to a QImage,
non-trivial computations and a transformation back to QBitmap.
See also QImage::createHeuristicMask().
int QPixmap::defaultDepth () [static]
Returns the default pixmap depth, i.e. the depth a pixmap gets
if -1 is specified.
See also depth().
QPixmap::Optimization QPixmap::defaultOptimization() [static]
Returns the default pixmap optimization setting.
See also setDefaultOptimization(), setOptimization() and optimization().
int QPixmap::depth () const
Returns the depth of the image.
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]
Special-purpose function that detaches the pixmap from shared pixmap data.
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 modifies the pixmap contents. In this case, 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.
Examples:
xform/xform.cpp
desktop/desktop.cpp
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 );
}
void QPixmap::fill ( const QWidget * widget, int xofs, int yofs )
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
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 widget has children, they are painted too, appropriately located.
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 returns 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, which gets the result of paintEvent(),
without e.g. overlying windows.
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 area 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]
Grabs the contents of a window and makes a pixmap out of it.
Returns the pixmap.
The arguments (x,y) specify the offset in the window, while
(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 grabWindows() grabs pixels from the screen, not from the
window. This means that 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().
int QPixmap::height () const
Returns the height of the pixmap.
See also width(), size() and rect().
Examples:
qtimage/qtimage.cpp
movies/main.cpp
xform/xform.cpp
desktop/desktop.cpp
scrollview/scrollview.cpp
const char* QPixmap::imageFormat ( const QString & fileName ) [static]
Returns a string that specifies the image format of the file fileName,
or null if the file cannot be read or if the format cannot be recognized.
The QImageIO documentation lists the supported image formats.
See also load() and save().
bool QPixmap::isNull () const
Returns TRUE if it is a null pixmap.
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:
qmag/qmag.cpp
scrollview/scrollview.cpp
bool QPixmap::isQBitmap () const
Returns TRUE if this is a QBitmap, otherwise FALSE.
bool QPixmap::load ( const QString & fileName, const char * format, int conversion_flags )
Loads a pixmap from the file fileName.
Returns TRUE if successful, or FALSE if the pixmap could not be loaded.
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 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
xform/xform.cpp
scrollview/scrollview.cpp
bool QPixmap::load ( const QString & fileName, const char * format=0, ColorMode mode=Auto )
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
bool QPixmap::loadFromData ( const uchar * buf, uint len, const char * format, int conversion_flags )
Loads a pixmap from the binary data in buf (len bytes).
Returns TRUE if successful, or FALSE if the pixmap could not be loaded.
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 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 QByteArray & buf, const char * format=0, int conversion_flags=0 )
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
bool QPixmap::loadFromData ( const uchar * buf, uint len, const char * format=0, ColorMode mode=Auto )
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
const QBitmap * QPixmap::mask () const
Returns the mask bitmap, or null if no mask has been set.
See also setMask() and QBitmap.
int QPixmap::metric ( int m ) const [virtual protected]
Internal implementation of the virtual QPaintDevice::metric() function.
Use the QPaintDeviceMetrics class instead.
Reimplemented from QPaintDevice.
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().
QPixmap & QPixmap::operator= ( const QPixmap & pixmap )
Assigns the pixmap pixmap to this pixmap and returns a reference to
this pixmap.
QPixmap::Optimization QPixmap::optimization() const
Returns the optimization setting for this pixmap.
The default optimization setting is QPixmap::NormalOptim. You may
change this settings in two ways:
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().
Examples:
xform/xform.cpp
void QPixmap::resize ( int w, int h )
Resizes the pixmap to w width and h height. If either w
or h is less than 1, the pixmap becomes a null pixmap.
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
void QPixmap::resize ( const QSize & size )
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
bool QPixmap::save ( const QString & fileName, const char * format ) const
Saves the pixmap to the file fileName, using the image file format
format. Returns TRUE if successful, or FALSE if the pixmap could not
be saved.
See also load(), loadFromData(), imageFormat(), QImage::save() and QImageIO.
bool QPixmap::save ( const QString & fileName, const char * format, int quality ) 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, or FALSE if the pixmap could not be saved.
See also load(), loadFromData(), imageFormat(), QImage::save() and QImageIO.
Examples:
qmag/qmag.cpp
bool QPixmap::selfMask () const
Returns TRUE if the pixmap's mask is identical to the pixmap itself.
See also mask().
int QPixmap::serialNumber () const
Returns a number that uniquely identifies the contents of this QPixmap object.
This means that multiple QPixmaps objects can have the same serial number
as long as they refer to the same contents.
The serial number is for example very useful for caching.
See also QPixmapCache.
void QPixmap::setDefaultOptimization ( Optimization optimization ) [static]
Sets the default pixmap optimization.
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 )
Sets a mask bitmap.
The mask bitmap defines the clip mask for this pixmap. Every pixel in
mask 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.
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().
Examples:
qtimage/qtimage.cpp
movies/main.cpp
QWMatrix QPixmap::trueMatrix ( const QWMatrix & matrix, int w, int h ) [static]
Returns the actual matrix used for transforming a pixmap with w
width and h height.
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:
qtimage/qtimage.cpp
movies/main.cpp
xform/xform.cpp
desktop/desktop.cpp
scrollview/scrollview.cpp
QPixmap QPixmap::xForm ( const QWMatrix & matrix ) const
Returns a copy of the pixmap that is transformed using matrix.
Qt uses this function to implement rotated text on window systems
that do not support such complex features.
Example of how to manually draw a rotated text at (100,200) in a widget:
char *str = "Trolls R Qt"; // text to be drawn
QFont f( "Charter", 24 ); // use Charter 24pt font
QPixmap pm( 8, 8 );
QPainter p;
QRect r; // text bounding rectangle
QPoint bl; // text baseline position
p.begin( &pm ); // first get the bounding
p.setFont( f ); // text rectangle
r = p.fontMetrics().boundingRect(str);
bl = -r.topLeft(); // get baseline position
p.end();
pm.resize( r.size() ); // resize to fit the text
pm.fill( white ); // fills pm with white
p.begin( &pm ); // begin painting pm
p.setFont( f ); // set the font
p.setPen( blue ); // set blue text color
p.drawText( bl, str ); // draw the text
p.end(); // painting done
QWMatrix m; // transformation matrix
m.rotate( -33.4 ); // rotate coordinate system
QPixmap rp = pm.xForm( m ); // rp is rotated pixmap
QWMatrix t = QPixmap::trueMatrix( m, pm.width(), pm.height() );
int x, y;
t.map( bl.x(),bl.y(), &x,&y ); // get pm's baseline pos in rp
bitBlt( myWidget, 100-x, 200-y, // blt rp into a widget
&rp, 0, 0, -1, -1 );
This example outlines how Qt implements rotated text under X11.
The font calculation is the most tedious part. The rotation itself is
only 3 lines of code.
If you want to draw rotated text, you do not have to implement all the
code above. The code below does exactly the same thing as the example
above, except that it uses a QPainter.
char *str = "Trolls R Qt"; // text to be drawn
QFont f( "Charter", 24 ); // use Charter 24pt font
QPainter p;
p.begin( myWidget );
p.translate( 100, 200 ); // translates coord system
p.rotate( -33.4 ); // rotates it counterclockwise
p.setFont( f );
p.drawText( 0, 0, str );
p.end();
See also trueMatrix(), QWMatrix and QPainter::setWorldMatrix().
Bugs and limitations:
- 2 and 4 bits pixmaps are not supported.
Examples:
qtimage/qtimage.cpp
movies/main.cpp
xform/xform.cpp
qmag/qmag.cpp
desktop/desktop.cpp
Related Functions
Reads a pixmap from the stream.
See also QPixmap::load() and Format of the QDataStream operators
Writes a pixmap to the stream as a PNG image.
See also QPixmap::save() and Format of the QDataStream operators
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