NAME

QwtGraphic - A paint device for scalable graphics.

SYNOPSIS

#include <qwt_graphic.h>

Inherits QwtNullPaintDevice.

Public Types

enum RenderHint { RenderPensUnscaled = 0x1 }
typedef QFlags< RenderHint > RenderHints
Render hints.

QwtGraphic ()
Constructor. QwtGraphic (const QwtGraphic &)
Copy constructor. virtual ~QwtGraphic ()
Destructor. QwtGraphic & operator= (const QwtGraphic &)
Assignment operator. void reset ()
Clear all stored commands. bool isNull () const
bool isEmpty () const
void render (QPainter *) const
Replay all recorded painter commands. void render (QPainter *, const QSizeF &, Qt::AspectRatioMode=Qt::IgnoreAspectRatio) const
Replay all recorded painter commands. void render (QPainter *, const QRectF &, Qt::AspectRatioMode=Qt::IgnoreAspectRatio) const
Replay all recorded painter commands. void render (QPainter *, const QPointF &, Qt::Alignment=Qt::AlignTop|Qt::AlignLeft) const
Replay all recorded painter commands. QPixmap toPixmap () const
Convert the graphic to a QPixmap. QPixmap toPixmap (const QSize &, Qt::AspectRatioMode=Qt::IgnoreAspectRatio) const
Convert the graphic to a QPixmap. QImage toImage () const
Convert the graphic to a QImage. QImage toImage (const QSize &, Qt::AspectRatioMode=Qt::IgnoreAspectRatio) const
Convert the graphic to a QImage. QRectF scaledBoundingRect (double sx, double sy) const
Calculate the target rectangle for scaling the graphic. QRectF boundingRect () const
QRectF controlPointRect () const
const QVector< QwtPainterCommand > & commands () const
void setCommands (QVector< QwtPainterCommand > &)
Append paint commands. void setDefaultSize (const QSizeF &)
Set a default size. QSizeF defaultSize () const
Default size. void setRenderHint (RenderHint, bool on=true)
bool testRenderHint (RenderHint) const

Protected Member Functions

virtual QSize sizeMetrics () const
virtual void drawPath (const QPainterPath &)
virtual void drawPixmap (const QRectF &, const QPixmap &, const QRectF &)
Store a pixmap command in the command list. virtual void drawImage (const QRectF &, const QImage &, const QRectF &, Qt::ImageConversionFlags)
Store a image command in the command list. virtual void updateState (const QPaintEngineState &state)
Store a state command in the command list.

Detailed Description

A paint device for scalable graphics.

QwtGraphic is the representation of a graphic that is tailored for scalability. Like QPicture it will be initialized by QPainter operations and can be replayed later to any target paint device.

While the usual image representations QImage and QPixmap are not scalable Qt offers two paint devices, that might be candidates for representing a vector graphic:

QPicture
Unfortunately QPicture had been forgotten, when Qt4 introduced floating point based render engines. Its API is still on integers, what make it unusable for proper scaling.
QSvgRenderer/QSvgGenerator
Unfortunately QSvgRenderer hides to much information about its nodes in internal APIs, that are necessary for proper layout calculations. Also it is derived from QObject and can't be copied like QImage/QPixmap.

QwtGraphic maps all scalable drawing primitives to a QPainterPath and stores them together with the painter state changes ( pen, brush, transformation ... ) in a list of QwtPaintCommands. For being a complete QPaintDevice it also stores pixmaps or images, what is somehow against the idea of the class, because these objects can't be scaled without a loss in quality.

The main issue about scaling a QwtGraphic object are the pens used for drawing the outlines of the painter paths. While non cosmetic pens ( QPen::isCosmetic() ) are scaled with the same ratio as the path, cosmetic pens have a fixed width. A graphic might have paths with different pens - cosmetic and non-cosmetic.

QwtGraphic caches 2 different rectangles:

control point rectangle
The control point rectangle is the bounding rectangle of all control point rectangles of the painter paths, or the target rectangle of the pixmaps/images.
bounding rectangle
The bounding rectangle extends the control point rectangle by what is needed for rendering the outline with an unscaled pen.

Because the offset for drawing the outline depends on the shape of the painter path ( the peak of a triangle is different than the flat side ) scaling with a fixed aspect ratio always needs to be calculated from the control point rectangle.

See also:

QwtPainterCommand

Member Typedef Documentation

typedef QFlags<RenderHint> QwtGraphic::RenderHints

Render hints. The default setting is to disable all hints

Member Enumeration Documentation

enum QwtGraphic::RenderHint

Hint how to render a graphic

See also:

setRenderHint(), testRenderHint()

Enumerator

RenderPensUnscaled: When rendering a QwtGraphic a specific scaling between the controlPointRect() and the coordinates of the target rectangle is set up internally in render().

When RenderPensUnscaled is set this specific scaling is applied for the control points only, but not for the pens. All other painter transformations ( set up by application code ) are supposed to work like usual.

See also:

render();

Constructor & Destructor Documentation

QwtGraphic::QwtGraphic ()

Constructor. Initializes a null graphic

See also:

isNull()

QwtGraphic::QwtGraphic (const QwtGraphic & other)

Copy constructor.

Store a image command in the command list.

Parameters:

rect traget rectangle
image Image to be painted
subRect Reactangle of the pixmap to be painted
flags Image conversion flags

See also:

QPaintEngine::drawImage()

Reimplemented from QwtNullPaintDevice.

void QwtGraphic::drawPath (const QPainterPath & path) [protected], [virtual]

Store a path command in the command list

Parameters:

path Painter path

See also:

QPaintEngine::drawPath()

Reimplemented from QwtNullPaintDevice.

void QwtGraphic::drawPixmap (const QRectF & rect, const QPixmap & pixmap, const QRectF & subRect) [protected], [virtual]

Store a pixmap command in the command list.

Parameters:

rect target rectangle
pixmap Pixmap to be painted
subRect Reactangle of the pixmap to be painted

See also:

QPaintEngine::drawPixmap()

Reimplemented from QwtNullPaintDevice.

bool QwtGraphic::isEmpty () const

Returns:

True, when the bounding rectangle is empty

See also:

boundingRect(), isNull()

bool QwtGraphic::isNull () const

Returns:

True, when no painter commands have been stored

See also:

isEmpty(), commands()

QwtGraphic & QwtGraphic::operator= (const QwtGraphic & other)

Assignment operator.

Parameters:

Calculate the target rectangle for scaling the graphic.

Parameters:

sx Horizontal scaling factor
sy Vertical scaling factor

Note:

In case of paths that are painted with a cosmetic pen ( see QPen::isCosmetic() ) the target rectangle is different to multiplying the bounding rectangle.

Returns:

Scaled bounding rectangle

See also:

boundingRect(), controlPointRect()

void QwtGraphic::setCommands (QVector< QwtPainterCommand > & commands)

Append paint commands.

Parameters:

commands Paint commands

See also:

commands()

void QwtGraphic::setDefaultSize (const QSizeF & size)

Set a default size. The default size is used in all methods rendering the graphic, where no size is explicitly specified. Assigning an empty size means, that the default size will be calculated from the bounding rectangle.

The default setting is an empty size.

Parameters:

size Default size

See also:

defaultSize(), boundingRect()

void QwtGraphic::setRenderHint (RenderHint hint, bool on = true)

Toggle an render hint

Parameters:

Convert the graphic to a QImage. All pixels of the image get initialized by 0 ( transparent ) before the graphic is scaled and rendered on it.

The format of the image is QImage::Format_ARGB32_Premultiplied.

Parameters:

size Size of the image
aspectRatioMode Aspect ratio how to scale the graphic

Returns:

The graphic as image

See also:

toPixmap(), render()

QPixmap QwtGraphic::toPixmap () const

Convert the graphic to a QPixmap. All pixels of the pixmap get initialized by Qt::transparent before the graphic is scaled and rendered on it.

The size of the pixmap is the default size ( ceiled to integers ) of the graphic.

Returns:

The graphic as pixmap in default size

See also:

defaultSize(), toImage(), render()

QPixmap QwtGraphic::toPixmap (const QSize & size, Qt::AspectRatioMode aspectRatioMode = Qt::IgnoreAspectRatio) const

Convert the graphic to a QPixmap. All pixels of the pixmap get initialized by Qt::transparent before the graphic is scaled and rendered on it.

Parameters:

size Size of the image
aspectRatioMode Aspect ratio how to scale the graphic

Returns:

The graphic as pixmap

See also:

toImage(), render()

void QwtGraphic::updateState (const QPaintEngineState & state) [protected], [virtual]

Store a state command in the command list.

Parameters:

state State to be stored

See also:

QPaintEngine::updateState()

Reimplemented from QwtNullPaintDevice.

Author

Generated automatically by Doxygen for Qwt User's Guide from the source code.