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QPaintEngine Class Reference

The QPaintEngine class provides an abstract definition of how QPainter draws to a given device on a given platform. More...

#include <QPaintEngine>

Part of the QtGui module.

Public Types

Public Functions


Detailed Description

The QPaintEngine class provides an abstract definition of how QPainter draws to a given device on a given platform.

Qt 4.0 provides several premade implementations of QPaintEngine for the different painter backends we support. We provide one paint engine for each window system and painting framework we support. This includes X11 on Unix/Linux, GDI/GDI+ on Windows and QuickDraw/CoreGraphics on Mac OS X. In addition we provide QPaintEngine implementations for OpenGL (accessible through QGLWidget) and PostScript (accessible through QPSPrinter on X11).

If one wants to use QPainter to draw to a different backend, such as PDF, one must subclass QPaintEngine and reimplement all its virtual functions. The QPaintEngine implementation is then made available by subclassing QPaintDevice and reimplementing the virtual function QPaintDevice::paintEngine().

QPaintEngine is created and owned by the QPaintDevice that created it.

The big advantage of the QPaintEngine approach opposed to the previous QPainter/QPaintDevice::cmd() approach is that it is now possible to adapt to multiple technologies on each platform and take advantage of the to the fullest.

See also QPainter and QPaintDevice::paintEngine().


Member Type Documentation

enum QPaintEngine::PaintEngineFeature
flags QPaintEngine::PaintEngineFeatures

This enum is used to describe the features or capabilities that the paint engine has. If a feature is not supported by the engine, QPainter will do a best effort to emulate that feature through other means. The features that are currently emulated are: CoordTransform, PixmapTransform, LinearGradientFill, PixmapScale, AlphaFill and ClipTransform.

ConstantValueDescription
QPaintEngine::CoordTransform0x000001The engine can transform the points in a drawing operation.
QPaintEngine::PenWidthTransform0x000002The engine has support for transforming pen widths.
QPaintEngine::PatternTransform0x000004The engine has support for transforming brush patterns.
QPaintEngine::PixmapTransform0x000010The engine can transform pixmaps, including rotation and shearing.
QPaintEngine::LinearGradientFill0x000020The engine can fill with linear gradients
QPaintEngine::LinearGradientFillPolygon0x000040The engine is capable of gradient fills in polygons only. Engines that support this feature and not regular gradient filling will have all primitives converted to polygons first so that this feature can be used instead.
QPaintEngine::PixmapScale0x000080The engine can scale pixmaps.
QPaintEngine::AlphaPixmap0x000800The engine can draw alpha pixmaps.
QPaintEngine::AlphaFill0x000100The engine can fill with alpha colors. If this feature is not specified, alpha filling can be emulated using alpha pixmaps.
QPaintEngine::AlphaFillPolygon0x000200The engine can fill polygons with alpha colors. Engines that specify this feature and not AlphaFill will have all primitives converted to polygons first, so that this feature can be used instead.
QPaintEngine::AlphaStroke0x000400The engine can draw outlines with alpha colors. Engines that do not support alphastroke can emulate it using AlphaFill, AlphaFillPolygon or AlphaPixmap.
QPaintEngine::PainterPaths0x001000The engine has path support.
QPaintEngine::ClipTransform0x002000The engine is capable of transforming clip regions.
QPaintEngine::PaintOutsidePaintEvent0x20000000The engine is capable of painting outside of paint events.
QPaintEngine::PatternBrush0x000008The engine is capable of rendering brushes with the brush patterns specified in Qt::BrushStyle.
QPaintEngine::LineAntialiasing0x004000The engine is capable of line antialiasing.
QPaintEngine::FillAntialiasing0x008000The engine is capable of fill antialiasing. If an engine is capable of fill, but not line antialiasing, line antialiasing will be emulated using a filled polygon that has the shape of the line.

The PaintEngineFeatures type stores an OR combination of PaintEngineFeature values.

enum QPaintEngine::PolygonDrawMode

ConstantValueDescription
QPaintEngine::OddEvenMode0The polygon should be drawn using OddEven fill rule.
QPaintEngine::WindingMode1The polygon should be drawn using Winding fill rule.
QPaintEngine::ConvexMode2The polygon is a convex polygon and can be drawn using specialized algorithms where available.
QPaintEngine::PolylineMode3Only the outline of the polygon should be drawn.

enum QPaintEngine::Type

ConstantValueDescription
QPaintEngine::X110 
QPaintEngine::Windows1 
QPaintEngine::Gdiplus (same as Windows)
QPaintEngine::QuickDraw2(same as CoreGraphics)
QPaintEngine::MacPrinter4 
QPaintEngine::CoreGraphics3Mac OS X
QPaintEngine::QWindowSystem5Qt/Embedded
QPaintEngine::PostScript6 
QPaintEngine::OpenGL7 
QPaintEngine::Picture8QPicture format
QPaintEngine::SVG9Scalable Vector Graphics XML format
QPaintEngine::User50First user type ID
QPaintEngine::MaxUser100Last user type ID

Member Function Documentation

QPaintEngine::QPaintEngine ( PaintEngineFeatures caps = 0 )

Creates a paint engine with the featureset specified by caps.

QPaintEngine::~QPaintEngine ()   [virtual]

Destroys the paint engine.

bool QPaintEngine::begin ( QPaintDevice * pdev )   [pure virtual]

Reimplement this function to initialise your paint engine when painting is to start on the paint device pdev. Return true if the initialization was successful; otherwise return false.

See also end() and isActive().

void QPaintEngine::drawEllipse ( const QRectF & rect )   [virtual]

Reimplement this function to draw the largest ellipse that can be contained within rectangle rect.

The default implementation calls drawPolygon().

See also drawPolygon.

void QPaintEngine::drawImage ( const QRectF & rectangle, const QImage & image, const QRectF & sr, Qt::ImageConversionFlags flags = Qt::AutoColor )   [virtual]

Reimplement this function to draw the part of the image specified by the sr rectangle in the given rectangle using the given conversion flags flags, to convert it to a pixmap.

void QPaintEngine::drawLine ( const QLineF & line )   [virtual]

The default implementation splits line into two points and calls the integer version of drawLine().

void QPaintEngine::drawLines ( const QLineF * lines, int lineCount )   [virtual]

Draws the first lineCount lines in the buffer lines

void QPaintEngine::drawPath ( const QPainterPath & path )   [virtual]

The default implementation ignores the path and does nothing.

void QPaintEngine::drawPixmap ( const QRectF & r, const QPixmap & pm, const QRectF & sr, Qt::PixmapDrawingMode mode = Qt::ComposePixmap )   [pure virtual]

Reimplement this function to draw the part of the pm specified by the sr rectangle in the given r using the given drawing mode.

void QPaintEngine::drawPoint ( const QPointF & pf )   [virtual]

The default implementation converts pf to an integer point and calls the integer version of drawPoint().

void QPaintEngine::drawPoints ( const QPointF * points, int pointCount )   [virtual]

Draws the first pointCount points in the buffer points

void QPaintEngine::drawPolygon ( const QPointF * points, int pointCount, PolygonDrawMode mode )   [virtual]

Reimplement this virtual function to draw the polygon defined by the pointCount first points in points, using mode mode.

The default implementation of this function will try to use drawPath if the engine supports the feature QPaintEngine::PainterPaths or try the int based drawPolygon() implementation if not.

void QPaintEngine::drawPolygon ( const QPoint * points, int pointCount, PolygonDrawMode mode )   [virtual]

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

Reimplement this virtual function to draw the polygon defined by the pointCount first points in points, using mode mode.

The default implementation of this function will try to use drawPath() if the engine supports the feature QPaintEngine::PainterPaths or try the float based drawPolygon() implementation if not.

void QPaintEngine::drawRect ( const QRectF & rf )   [virtual]

The default implementation converts rf to an integer rectangle and calls the integer version of drawRect().

void QPaintEngine::drawRects ( const QRectF * rects, int rectCount )   [virtual]

Draws the first rectCount rectangles in the buffer rects.

void QPaintEngine::drawTextItem ( const QPointF & p, const QTextItem & textItem )   [virtual]

This function draws the text item textItem at position p. The default implementation of this function converts the text to a QPainterPath and paints the resulting path.

void QPaintEngine::drawTiledPixmap ( const QRectF & rect, const QPixmap & pixmap, const QPointF & p, Qt::PixmapDrawingMode mode = Qt::ComposePixmap )   [virtual]

Reimplement this function to draw the pixmap in the given rect, starting at the given p. The pixmap will be drawn repeatedly until the rect is filled using the given mode.

bool QPaintEngine::end ()   [pure virtual]

Reimplement this function to finish painting on the current paint device. Return true if painting was finished successfully; otherwise return false.

See also begin() and isActive().

bool QPaintEngine::hasFeature ( PaintEngineFeatures feature ) const

Returns true if the paint engine supports the specified feature; otherwise returns false.

bool QPaintEngine::isActive () const

Returns true if the paint engine is actively drawing; otherwise returns false.

See also setActive().

QPaintDevice * QPaintEngine::paintDevice () const

Returns the engine that this engine is painting on, if painting is active; otherwise returns 0.

QPainter * QPaintEngine::painter () const

Returns the paint engine's painter.

QPainter::RenderHints QPaintEngine::renderHints () const

Returns the currently set renderhints.

void QPaintEngine::setActive ( bool state )

Sets the active state of the paint engine to state.

See also isActive().

void QPaintEngine::setRenderHint ( QPainter::RenderHint hint, bool on )

Sets the render hint hint on this engine if on is true; otherwise clears the render hint.

QPainter::RenderHints QPaintEngine::supportedRenderHints () const   [virtual]

Returns the set of supported renderhints.

Type QPaintEngine::type () const   [pure virtual]

Reimplement this function to return the paint engine Type.

void QPaintEngine::updateBackground ( Qt::BGMode bgmode, const QBrush & brush )   [pure virtual]

This function is called when the engine needs to be updated with new background settings. bgmode describes the background mode and brush describes the background brush.

void QPaintEngine::updateBrush ( const QBrush & brush, const QPointF & origin )   [pure virtual]

This function is called when the engine needs to be updated with a new brush, specified with brush. origin describes the brush origin.

If the brush is a gradient brush, the gradient points are specified in device coordinates.

void QPaintEngine::updateClipPath ( const QPainterPath & path, Qt::ClipOperation op )   [virtual]

This function is called when the engine needs to be updated with the new clip path. The value of op specifies how the clip path should be combined with the current clip.

void QPaintEngine::updateClipRegion ( const QRegion & region, Qt::ClipOperation op )   [pure virtual]

This function is called when the clip region changes. The clip operation op specifies how the new region region should be combined (if at all) with the new region.

void QPaintEngine::updateFont ( const QFont & f )   [pure virtual]

This function is called when the engine needs to be updated with a new font, specified by f

void QPaintEngine::updateMatrix ( const QMatrix & matrix )   [pure virtual]

This function is called when the engine needs to be updated with new transformation settings, specified with matrix.

void QPaintEngine::updatePen ( const QPen & pen )   [pure virtual]

This function is called when the engine needs to be updated with the a new pen, specified by pen.

void QPaintEngine::updateRenderHints ( QPainter::RenderHints hints )   [virtual]

This function is caleed when the engine needs to be updated with the new set of renderhints specified by hints.


Copyright © 2005 Trolltech Trademarks
Qt 4.0.0-b2