CopperSpice API  1.7.2
QPaintDevice Class Referenceabstract

The QPaintDevice class is the base class of objects that can be painted. More...

Inheritance diagram for QPaintDevice:
QGLFramebufferObject QGLPixelBuffer QImage QPagedPaintDevice QPaintDeviceWindow QPicture QPixmap QSvgGenerator QWidget

Public Types

enum  PaintDeviceMetric
 

Public Methods

virtual ~QPaintDevice ()
 
int colorCount () const
 
int depth () const
 
int devicePixelRatio () const
 
qreal devicePixelRatioF () const
 
int height () const
 
int heightMM () const
 
int logicalDpiX () const
 
int logicalDpiY () const
 
virtual QPaintEnginepaintEngine () const = 0
 
bool paintingActive () const
 
int physicalDpiX () const
 
int physicalDpiY () const
 
int width () const
 
int widthMM () const
 

Protected Methods

 QPaintDevice ()
 
virtual int metric (PaintDeviceMetric metric) const
 

Friends

class QPainter
 

Detailed Description

The QPaintDevice class is the base class of objects that can be painted.

A paint device is an abstraction of a two-dimensional space that can be drawn using a QPainter. Its default coordinate system has its origin located at the top-left position. X increases to the right and Y increases downwards. The unit is one pixel.

The drawing capabilities of QPaintDevice are currently implemented by the QWidget, QImage, QPixmap, QGLPixelBuffer, QPicture, and QPrinter subclasses.

To implement support for a new backend, you must derive from QPaintDevice and reimplement the virtual paintEngine() function to tell QPainter which paint engine should be used to draw on this particular device. Note that you also must create a corresponding paint engine to be able to draw on the device, i.e derive from QPaintEngine and reimplement its virtual functions.

CopperSpice requires that a QApplication object exists before any paint devices can be created. Paint devices access window system resources, and these resources are not initialized before an application object is created.

The QPaintDevice class provides several functions returning the various device metrics: The depth() function returns its bit depth (number of bit planes). The height() function returns its height in default coordinate system units (e.g. pixels for QPixmap and QWidget) while heightMM() returns the height of the device in millimeters. The width() and widthMM() functions return the width of the device in default coordinate system units and in millimeters, respectively. Alternatively, the protected metric() function can be used to retrieve the metric information by specifying the desired PaintDeviceMetric as argument.

The logicalDpiX() and logicalDpiY() functions return the horizontal and vertical resolution of the device in dots per inch. The physicalDpiX() and physicalDpiY() functions also return the resolution of the device in dots per inch, but note that if the logical and physical resolution differ, the corresponding QPaintEngine must handle the mapping. Finally, the colorCount() function returns the number of different colors available for the paint device.

See also
QPaintEngine, QPainter, ref coordsys "Coordinate System", Paint System

Member Enumeration Documentation

Describes the various metrics of a paint device.

ConstantValueDescription
QPaintDevice::PdmWidth 1 The width of the paint device in default coordinate system units (e.g. pixels for QPixmap and QWidget). Refer to width().
QPaintDevice::PdmHeight 2 The height of the paint device in default coordinate system units (e.g. pixels for QPixmap and QWidget). Refer to height().
QPaintDevice::PdmWidthMM3 The width of the paint device in millimeters. Refer to widthMM().
QPaintDevice::PdmHeightMM4 The height of the paint device in millimeters. Refer to heightMM().
QPaintDevice::PdmNumColors5 The number of different colors available for the paint device. Refer to colorCount().
QPaintDevice::PdmDepth6 The bit depth (number of bit planes) of the paint device. Refer to depth().
QPaintDevice::PdmDpiX7 The horizontal resolution of the device in dots per inch. Refer to logicalDpiX().
QPaintDevice::PdmDpiY8 The vertical resolution of the device in dots per inch. Refer to logicalDpiY().
QPaintDevice::PdmPhysicalDpiX9 The horizontal resolution of the device in dots per inch. Refer to physicalDpiX().
QPaintDevice::PdmPhysicalDpiY10 The vertical resolution of the device in dots per inch. Refer to physicalDpiY().
See also
metric()

Constructor & Destructor Documentation

QPaintDevice::~QPaintDevice ( )
virtual

Destroys the paint device and frees window system resources.

QPaintDevice::QPaintDevice ( )
protected

Constructs a paint device. This constructor can be invoked only from subclasses of QPaintDevice.

Method Documentation

int QPaintDevice::colorCount ( ) const
inline

Returns the number of different colors available for the paint device. Since this value is an int, it will not be sufficient to represent the number of colors on 32 bit displays, in this case INT_MAX is returned instead.

int QPaintDevice::depth ( ) const
inline

Returns the bit depth (number of bit planes) of the paint device.

int QPaintDevice::devicePixelRatio ( ) const
inline

Returns the device pixel ratio for device. Common values are 1 for normal DPI displays and 2 for high DPI displays.

qreal QPaintDevice::devicePixelRatioF ( ) const
inline

Returns the device pixel ratio for the device as a floating point number.

int QPaintDevice::height ( ) const
inline

Returns the height of the paint device in default coordinate system units (e.g. pixels for QPixmap and QWidget).

See also
heightMM()
int QPaintDevice::heightMM ( ) const
inline

Returns the height of the paint device in millimeters. Due to platform limitations it may not be possible to use this function to determine the actual physical size of a widget on the screen.

See also
height()
int QPaintDevice::logicalDpiX ( ) const
inline

Returns the horizontal resolution of the device in dots per inch, which is used when computing font sizes. For X11, this is usually the same as could be computed from widthMM().

If the logicalDpiX() does not equal the physicalDpiX() then the corresponding QPaintEngine must handle the resolution mapping.

See also
logicalDpiY(), physicalDpiX()
int QPaintDevice::logicalDpiY ( ) const
inline

Returns the vertical resolution of the device in dots per inch, which is used when computing font sizes. For X11, this is usually the same as could be computed from heightMM().

If the logicalDpiY() does not equal the physicalDpiY() then the corresponding QPaintEngine must handle the resolution mapping.

See also
logicalDpiX(), physicalDpiY()
int QPaintDevice::metric ( PaintDeviceMetric  metric) const
protectedvirtual

Returns the metric information for the given paint device metric.

See also
PaintDeviceMetric

Reimplemented in QSvgGenerator, QOpenGLWidget, QPrinter, QPixmap, QWidget, QImage, QGLFramebufferObject, QOpenGLWindow, QGLPixelBuffer, QPaintDeviceWindow, QRasterWindow, QPicture, and QPdfWriter.

QPaintEngine * QPaintDevice::paintEngine ( ) const
pure virtual

Returns a pointer to the paint engine used for drawing on the device.

Implemented in QWidget, QGLWidget, QImage, QPrinter, QPixmap, QSvgGenerator, QOpenGLWidget, QPicture, QPdfWriter, QGLFramebufferObject, and QGLPixelBuffer.

bool QPaintDevice::paintingActive ( ) const
inline

Returns true if the device is currently being painted on, i.e. someone has called QPainter::begin() but not yet called QPainter::end() for this device, otherwise returns false.

See also
QPainter::isActive()
int QPaintDevice::physicalDpiX ( ) const
inline

Returns the horizontal resolution of the device in dots per inch. For example, when printing the resolution refers to the physical printer's resolution. The logical DPI on the other hand, refers to the resolution used by the actual paint engine.

If the physicalDpiX() does not equal the logicalDpiX() then the corresponding QPaintEngine must handle the resolution mapping.

See also
physicalDpiY(), logicalDpiX()
int QPaintDevice::physicalDpiY ( ) const
inline

Returns the horizontal resolution of the device in dots per inch. For example, when printing the resolution refers to the physical printer's resolution. The logical DPI on the other hand, refers to the resolution used by the actual paint engine.

If the physicalDpiY() does not equal the logicalDpiY() then the corresponding QPaintEngine must handle the resolution mapping.

See also
physicalDpiX(), logicalDpiY()
int QPaintDevice::width ( ) const
inline

Returns the width of the paint device in default coordinate system units (e.g. pixels for QPixmap and QWidget).

See also
widthMM()
int QPaintDevice::widthMM ( ) const
inline

Returns the width of the paint device in millimeters. Due to platform limitations it may not be possible to use this function to determine the actual physical size of a widget on the screen.

See also
width()