Contents

• Public Types
• Public Functions
• Detailed Description

Detailed Description

TheQPaintEngine class provides an abstract definition of howQPainter draws to a given device on a given platform.

Qt 4.0 provides several premade implementations ofQPaintEngine 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 andCoreGraphics on Mac OS X. In addition we provideQPaintEngine implementations forOpenGL (accessible throughQGLWidget) andPostScript (accessible through QPSPrinter on X11). Additionally there is a raster-based paint engine that is a fallback for when an engine does not support a certain capability.

If one wants to useQPainter to draw to a different backend, one must subclassQPaintEngine and reimplement all its virtual functions. TheQPaintEngine implementation is then made available by subclassingQPaintDevice and reimplementing the virtual functionQPaintDevice::paintEngine().

QPaintEngine is created and owned by theQPaintDevice that created it.

The big advantage of theQPaintEngine approach opposed to Qt 3'sQPainter/QPaintDevice::cmd() approach is that it is now possible to adapt to multiple technologies on each platform and take advantage of each to the fullest.

Member Type Documentation

enum QPaintEngine::DirtyFlag
flags QPaintEngine::DirtyFlags

These types are used byQPainter to trigger lazy updates of the various states in theQPaintEngine usingQPaintEngine::updateState().

A paint engine must update every dirty state.

The DirtyFlags type is a typedef forQFlags<DirtyFlag>. It stores an OR combination of DirtyFlag values.

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 and pass on an alpha blendedQImage to the engine with the emulated results. Some features cannot be emulated: AlphaBlend and PorterDuff.

The PaintEngineFeatures type is a typedef forQFlags<PaintEngineFeature>. It stores an OR combination of PaintEngineFeature values.

enum QPaintEngine::PolygonDrawMode

enum QPaintEngine::Type

Member Function Documentation

QPaintEngine::QPaintEngine(PaintEngineFeatures caps = 0)

Creates a paint engine with the featureset specified bycaps.

[virtual]QPaintEngine::~QPaintEngine()

Destroys the paint engine.

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

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

See alsoend() andisActive().

[virtual]void QPaintEngine::drawEllipse(constQRectF & rect)

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

The default implementation callsdrawPolygon().

[virtual]void QPaintEngine::drawEllipse(constQRect & rect)

The default implementation of this function calls the floating point version of this function

[virtual]void QPaintEngine::drawImage(constQRectF & rectangle, constQImage & image, constQRectF & sr,Qt::ImageConversionFlags flags = Qt::AutoColor)

Reimplement this function to draw the part of theimage specified by thesr rectangle in the givenrectangle using the given conversion flagsflags, to convert it to a pixmap.

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

The default implementation splits the list of lines inlines intolineCount separate calls todrawPath() ordrawPolygon() depending on the feature set of the paint engine.

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

This is an overloaded function.

The default implementation converts the firstlineCount lines inlines to aQLineF and calls the floating point version of this function.

[virtual]void QPaintEngine::drawPath(constQPainterPath & path)

The default implementation ignores thepath and does nothing.

[pure virtual]void QPaintEngine::drawPixmap(constQRectF & r, constQPixmap & pm, constQRectF & sr)

Reimplement this function to draw the part of thepm specified by thesr rectangle in the givenr.

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

Draws the firstpointCount points in the bufferpoints

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

Draws the firstpointCount points in the bufferpoints

The default implementation converts the firstpointCount QPoints inpoints to QPointFs and calls the floating point version ofdrawPoints.

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

Reimplement this virtual function to draw the polygon defined by thepointCount first points inpoints, using modemode.

Note:At least one of the drawPolygon() functions must be reimplemented.

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

This is an overloaded function.

Reimplement this virtual function to draw the polygon defined by thepointCount first points inpoints, using modemode.

Note:At least one of thedrawPolygon() functions must be reimplemented.

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

Draws the firstrectCount rectangles in the bufferrects. The default implementation of this function callsdrawPath() ordrawPolygon() depending on the feature set of the paint engine.

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

This is an overloaded function.

The default implementation converts the firstrectCount rectangles in the bufferrects to aQRectF and calls the floating point version of this function.

[virtual]void QPaintEngine::drawTextItem(constQPointF & p, constQTextItem & textItem)

This function draws the text itemtextItem at positionp. The default implementation of this function converts the text to aQPainterPath and paints the resulting path.

[virtual]void QPaintEngine::drawTiledPixmap(constQRectF & rect, constQPixmap & pixmap, constQPointF & p)

Reimplement this function to draw thepixmap in the givenrect, starting at the givenp. The pixmap will be drawn repeatedly until therect is filled.

[pure virtual]bool QPaintEngine::end()

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

See alsobegin() andisActive().

bool QPaintEngine::hasFeature(PaintEngineFeatures feature) const

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

bool QPaintEngine::isActive() const

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

See alsosetActive().

QPaintDevice * QPaintEngine::paintDevice() const

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

QPainter * QPaintEngine::painter() const

Returns the paint engine's painter.

void QPaintEngine::setActive(bool state)

Sets the active state of the paint engine tostate.

See alsoisActive().

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

Reimplement this function to return the paint engineType.

[pure virtual]void QPaintEngine::updateState(constQPaintEngineState & state)

Reimplement this function to update the state of a paint engine.

When implemented, this function is responsible for checking the paint engine's currentstate and update the properties that are changed. Use theQPaintEngineState::state() function to find out which properties that must be updated, then use the correspondingget function to retrieve the current values for the given properties.

See alsoQPaintEngineState.