QwtGraphic - Man Page

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.

Public Member Functions

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:

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:

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.

Parameters

other Source

See also

operator=()

Member Function Documentation

QRectF QwtGraphic::boundingRect () const

The bounding rectangle is the controlPointRect() extended by the areas needed for rendering the outlines with unscaled pens.

Returns

Bounding rectangle of the graphic

See also

controlPointRect(), scaledBoundingRect()

const QVector< QwtPainterCommand > & QwtGraphic::commands () const

Returns

List of recorded paint commands

See also

setCommands()

QRectF QwtGraphic::controlPointRect () const

The control point rectangle is the bounding rectangle of all control points of the paths and the target rectangles of the images/pixmaps.

Returns

Control point rectangle

See also

boundingRect(), scaledBoundingRect()

QSizeF QwtGraphic::defaultSize () const

Default size. When a non empty size has been assigned by setDefaultSize() this size will be returned. Otherwise the default size is the size of the bounding rectangle.

The default size is used in all methods rendering the graphic, where no size is explicitly specified.

Returns

Default size

See also

setDefaultSize(), boundingRect()

void QwtGraphic::drawImage (const QRectF & rect, const QImage & image, const QRectF & subRect, Qt::ImageConversionFlags flags) [protected], [virtual]

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

other Source

Returns

A reference of this object

void QwtGraphic::render (QPainter * painter) const

Replay all recorded painter commands.

Parameters

painter Qt painter

void QwtGraphic::render (QPainter * painter, const QPointF & pos, Qt::Alignment alignment = Qt::AlignTop | Qt::AlignLeft) const

Replay all recorded painter commands. The graphic is scaled to the defaultSize() and aligned to a position.

Parameters

painter Qt painter
pos Reference point, where to render
alignment Flags how to align the target rectangle to pos.

void QwtGraphic::render (QPainter * painter, const QRectF & rect, Qt::AspectRatioMode aspectRatioMode = Qt::IgnoreAspectRatio) const

Replay all recorded painter commands. The graphic is scaled to fit into the given rectangle

Parameters

painter Qt painter
rect Rectangle for the scaled graphic
aspectRatioMode Mode how to scale - See Qt::AspectRatioMode

void QwtGraphic::render (QPainter * painter, const QSizeF & size, Qt::AspectRatioMode aspectRatioMode = Qt::IgnoreAspectRatio) const

Replay all recorded painter commands. The graphic is scaled to fit into the rectangle of the given size starting at ( 0, 0 ).

Parameters

painter Qt painter
size Size for the scaled graphic
aspectRatioMode Mode how to scale - See Qt::AspectRatioMode

void QwtGraphic::reset ()

Clear all stored commands.

See also

isNull()

QRectF QwtGraphic::scaledBoundingRect (double sx, double sy) const

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

hint Render hint
on true/false

See also

testRenderHint(), RenderHint

QSize QwtGraphic::sizeMetrics () const [protected], [virtual]

Returns

Ceiled defaultSize()

Implements QwtNullPaintDevice.

bool QwtGraphic::testRenderHint (RenderHint hint) const

Test a render hint

Parameters

hint Render hint

Returns

true/false

See also

setRenderHint(), RenderHint

QImage QwtGraphic::toImage () const

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.

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

Returns

The graphic as image in default size

See also

defaultSize(), toPixmap(), render()

QImage QwtGraphic::toImage (const QSize & size, Qt::AspectRatioMode aspectRatioMode = Qt::IgnoreAspectRatio) const

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

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Info

Mon Jun 1 2020 Version 6.1.5 Qwt User's Guide