Qwt User's Guide
QwtGraphic Class Reference

A paint device for scalable graphics. More...

#include <qwt_graphic.h>

Inheritance diagram for QwtGraphic:

Public Types

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

Public Member Functions

 QwtGraphic ()
 Constructor.
 QwtGraphic (const QwtGraphic &)
 Copy constructor.
virtual ~QwtGraphic ()
 Destructor.
QwtGraphicoperator= (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

Render hints.

The default setting is to disable all hints


Member Enumeration Documentation

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

Constructor.

Initializes a null graphic

See also:
isNull()
QwtGraphic::QwtGraphic ( const QwtGraphic other)

Copy constructor.

Parameters:
otherSource
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:
recttraget rectangle
imageImage to be painted
subRectReactangle of the pixmap to be painted
flagsImage 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:
pathPainter 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:
recttarget rectangle
pixmapPixmap to be painted
subRectReactangle 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:
otherSource
Returns:
A reference of this object
void QwtGraphic::render ( QPainter *  painter) const

Replay all recorded painter commands.

Parameters:
painterQt painter
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:
painterQt painter
sizeSize for the scaled graphic
aspectRatioModeMode how to scale - See Qt::AspectRatioMode
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:
painterQt painter
rectRectangle for the scaled graphic
aspectRatioModeMode how to scale - See Qt::AspectRatioMode
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:
painterQt painter
posReference point, where to render
alignmentFlags how to align the target rectangle to pos.

Clear all stored commands.

See also:
isNull()
QRectF QwtGraphic::scaledBoundingRect ( double  sx,
double  sy 
) const

Calculate the target rectangle for scaling the graphic.

Parameters:
sxHorizontal scaling factor
syVertical 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:
commandsPaint 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:
sizeDefault size
See also:
defaultSize(), boundingRect()
void QwtGraphic::setRenderHint ( RenderHint  hint,
bool  on = true 
)

Toggle an render hint

Parameters:
hintRender hint
ontrue/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:
hintRender 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:
sizeSize of the image
aspectRatioModeAspect 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:
sizeSize of the image
aspectRatioModeAspect 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:
stateState to be stored
See also:
QPaintEngine::updateState()

Reimplemented from QwtNullPaintDevice.

List of all members.

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