Qwt User's Guide  6.2.0
QwtPlotRasterItem Class Referenceabstract

A class, which displays raster data. More...

#include <qwt_plot_rasteritem.h>

Inheritance diagram for QwtPlotRasterItem:

Public Types

enum  CachePolicy { NoCache , PaintCache }
 Cache policy The default policy is NoCache. More...
 
enum  PaintAttribute { PaintInDeviceResolution = 1 }
 
typedef QFlags< PaintAttributePaintAttributes
 
- Public Types inherited from QwtPlotItem
enum  RttiValues {
  Rtti_PlotItem = 0 , Rtti_PlotGrid , Rtti_PlotScale , Rtti_PlotLegend ,
  Rtti_PlotMarker , Rtti_PlotCurve , Rtti_PlotSpectroCurve , Rtti_PlotIntervalCurve ,
  Rtti_PlotHistogram , Rtti_PlotSpectrogram , Rtti_PlotGraphic , Rtti_PlotTradingCurve ,
  Rtti_PlotBarChart , Rtti_PlotMultiBarChart , Rtti_PlotShape , Rtti_PlotTextLabel ,
  Rtti_PlotZone , Rtti_PlotVectorField , Rtti_PlotUserItem = 1000
}
 Runtime type information. More...
 
enum  ItemAttribute { Legend = 0x01 , AutoScale = 0x02 , Margins = 0x04 }
 Plot Item Attributes. More...
 
enum  ItemInterest { ScaleInterest = 0x01 , LegendInterest = 0x02 }
 Plot Item Interests. More...
 
enum  RenderHint { RenderAntialiased = 0x1 }
 Render hints. More...
 
typedef QFlags< ItemAttributeItemAttributes
 
typedef QFlags< ItemInterestItemInterests
 
typedef QFlags< RenderHintRenderHints
 

Public Member Functions

 QwtPlotRasterItem (const QString &title=QString())
 Constructor.
 
 QwtPlotRasterItem (const QwtText &title)
 Constructor.
 
virtual ~QwtPlotRasterItem ()
 Destructor.
 
void setPaintAttribute (PaintAttribute, bool on=true)
 
bool testPaintAttribute (PaintAttribute) const
 
void setAlpha (int alpha)
 Set an alpha value for the raster data. More...
 
int alpha () const
 
void setCachePolicy (CachePolicy)
 
CachePolicy cachePolicy () const
 
void invalidateCache ()
 
virtual void draw (QPainter *, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &canvasRect) const override
 Draw the raster data. More...
 
virtual QRectF pixelHint (const QRectF &) const
 Pixel hint. More...
 
virtual QwtInterval interval (Qt::Axis) const
 
virtual QRectF boundingRect () const override
 
- Public Member Functions inherited from QwtPlotItem
 QwtPlotItem ()
 
 QwtPlotItem (const QString &title)
 
 QwtPlotItem (const QwtText &title)
 
virtual ~QwtPlotItem ()
 Destroy the QwtPlotItem.
 
void attach (QwtPlot *plot)
 Attach the item to a plot. More...
 
void detach ()
 This method detaches a QwtPlotItem from any QwtPlot it has been associated with. More...
 
QwtPlotplot () const
 Return attached plot.
 
void setTitle (const QString &title)
 
void setTitle (const QwtText &title)
 
const QwtTexttitle () const
 
virtual int rtti () const
 
void setItemAttribute (ItemAttribute, bool on=true)
 
bool testItemAttribute (ItemAttribute) const
 
void setItemInterest (ItemInterest, bool on=true)
 
bool testItemInterest (ItemInterest) const
 
void setRenderHint (RenderHint, bool on=true)
 
bool testRenderHint (RenderHint) const
 
void setRenderThreadCount (uint numThreads)
 
uint renderThreadCount () const
 
void setLegendIconSize (const QSize &)
 
QSize legendIconSize () const
 
double z () const
 
void setZ (double z)
 Set the z value. More...
 
void show ()
 Show the item.
 
void hide ()
 Hide the item.
 
virtual void setVisible (bool)
 
bool isVisible () const
 
void setAxes (QwtAxisId xAxis, QwtAxisId yAxis)
 
void setXAxis (QwtAxisId)
 
QwtAxisId xAxis () const
 Return xAxis.
 
void setYAxis (QwtAxisId)
 
QwtAxisId yAxis () const
 Return yAxis.
 
virtual void itemChanged ()
 
virtual void legendChanged ()
 
virtual void getCanvasMarginHint (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &canvasRect, double &left, double &top, double &right, double &bottom) const
 Calculate a hint for the canvas margin. More...
 
virtual void updateScaleDiv (const QwtScaleDiv &, const QwtScaleDiv &)
 Update the item to changes of the axes scale division. More...
 
virtual void updateLegend (const QwtPlotItem *, const QList< QwtLegendData > &)
 Update the item to changes of the legend info. More...
 
QRectF scaleRect (const QwtScaleMap &, const QwtScaleMap &) const
 Calculate the bounding scale rectangle of 2 maps. More...
 
QRectF paintRect (const QwtScaleMap &, const QwtScaleMap &) const
 Calculate the bounding paint rectangle of 2 maps. More...
 
virtual QList< QwtLegendDatalegendData () const
 Return all information, that is needed to represent the item on the legend. More...
 
virtual QwtGraphic legendIcon (int index, const QSizeF &) const
 

Protected Member Functions

virtual QImage renderImage (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &area, const QSize &imageSize) const =0
 Render an image. More...
 
virtual QwtScaleMap imageMap (Qt::Orientation, const QwtScaleMap &map, const QRectF &area, const QSize &imageSize, double pixelSize) const
 Calculate a scale map for painting to an image. More...
 
- Protected Member Functions inherited from QwtPlotItem
QwtGraphic defaultIcon (const QBrush &, const QSizeF &) const
 Return a default icon from a brush. More...
 

Detailed Description

A class, which displays raster data.

Raster data is a grid of pixel values, that can be represented as a QImage. It is used for many types of information like spectrograms, cartograms, geographical maps ...

Often a plot has several types of raster data organized in layers. ( f.e a geographical map, with weather statistics ). Using setAlpha() raster items can be stacked easily.

QwtPlotRasterItem is only implemented for images of the following formats: QImage::Format_Indexed8, QImage::Format_ARGB32.

See also
QwtPlotSpectrogram

Definition at line 37 of file qwt_plot_rasteritem.h.

Member Typedef Documentation

◆ PaintAttributes

An ORed combination of PaintAttribute values.

Definition at line 83 of file qwt_plot_rasteritem.h.

Member Enumeration Documentation

◆ CachePolicy

Cache policy The default policy is NoCache.

Enumerator
NoCache 

renderImage() is called each time the item has to be repainted

PaintCache 

renderImage() is called, whenever the image cache is not valid, or the scales, or the size of the canvas has changed.

This type of cache is useful for improving the performance of hide/show operations or manipulations of the alpha value. All other situations are handled by the canvas backing store.

Definition at line 44 of file qwt_plot_rasteritem.h.

◆ PaintAttribute

Attributes to modify the drawing algorithm.

See also
setPaintAttribute(), testPaintAttribute()
Enumerator
PaintInDeviceResolution 

When the image is rendered according to the data pixels ( QwtRasterData::pixelHint() ) it can be expanded to paint device resolution before it is passed to QPainter. The expansion algorithm rounds the pixel borders in the same way as the axis ticks, what is usually better than the scaling algorithm implemented in Qt. Disabling this flag might make sense, to reduce the size of a document/file. If this is possible for a document format depends on the implementation of the specific QPaintEngine.

Definition at line 66 of file qwt_plot_rasteritem.h.

Member Function Documentation

◆ alpha()

int QwtPlotRasterItem::alpha ( ) const
Returns
Alpha value of the raster item
See also
setAlpha()

Definition at line 530 of file qwt_plot_rasteritem.cpp.

◆ boundingRect()

QRectF QwtPlotRasterItem::boundingRect ( ) const
overridevirtual
Returns
Bounding rectangle of the data
See also
QwtPlotRasterItem::interval()

Reimplemented from QwtPlotItem.

Definition at line 788 of file qwt_plot_rasteritem.cpp.

◆ cachePolicy()

QwtPlotRasterItem::CachePolicy QwtPlotRasterItem::cachePolicy ( ) const
Returns
Cache policy
See also
CachePolicy, setCachePolicy()

Definition at line 559 of file qwt_plot_rasteritem.cpp.

◆ draw()

void QwtPlotRasterItem::draw ( QPainter *  painter,
const QwtScaleMap xMap,
const QwtScaleMap yMap,
const QRectF &  canvasRect 
) const
overridevirtual

Draw the raster data.

Parameters
painterPainter
xMapX-Scale Map
yMapY-Scale Map
canvasRectContents rectangle of the plot canvas

Implements QwtPlotItem.

Reimplemented in QwtPlotSpectrogram.

Definition at line 614 of file qwt_plot_rasteritem.cpp.

◆ imageMap()

QwtScaleMap QwtPlotRasterItem::imageMap ( Qt::Orientation  orientation,
const QwtScaleMap map,
const QRectF &  area,
const QSize &  imageSize,
double  pixelSize 
) const
protectedvirtual

Calculate a scale map for painting to an image.

Parameters
orientationOrientation, Qt::Horizontal means a X axis
mapScale map for rendering the plot item
areaArea to be painted on the image
imageSizeImage size
pixelSizeWidth/Height of a data pixel
Returns
Calculated scale map

Definition at line 927 of file qwt_plot_rasteritem.cpp.

◆ interval()

QwtInterval QwtPlotRasterItem::interval ( Qt::Axis  axis) const
virtual
Returns
Bounding interval for an axis

This method is intended to be reimplemented by derived classes. The default implementation returns an invalid interval.

Parameters
axisX, Y, or Z axis

Reimplemented in QwtPlotSpectrogram.

Definition at line 778 of file qwt_plot_rasteritem.cpp.

◆ invalidateCache()

void QwtPlotRasterItem::invalidateCache ( )

Invalidate the paint cache

See also
setCachePolicy()

Definition at line 568 of file qwt_plot_rasteritem.cpp.

◆ pixelHint()

QRectF QwtPlotRasterItem::pixelHint ( const QRectF &  area) const
virtual

Pixel hint.

The geometry of a pixel is used to calculated the resolution and alignment of the rendered image.

Width and height of the hint need to be the horizontal and vertical distances between 2 neighbored points. The center of the hint has to be the position of any point ( it doesn't matter which one ).

Limiting the resolution of the image might significantly improve the performance and heavily reduce the amount of memory when rendering a QImage from the raster data.

The default implementation returns an empty rectangle (QRectF()), meaning, that the image will be rendered in target device ( f.e screen ) resolution.

Parameters
areaIn most implementations the resolution of the data doesn't depend on the requested area.
Returns
Bounding rectangle of a pixel
See also
render(), renderImage()

Reimplemented in QwtPlotSpectrogram.

Definition at line 601 of file qwt_plot_rasteritem.cpp.

◆ renderImage()

virtual QImage QwtPlotRasterItem::renderImage ( const QwtScaleMap xMap,
const QwtScaleMap yMap,
const QRectF &  area,
const QSize &  imageSize 
) const
protectedpure virtual

Render an image.

An implementation of render() might iterate over all pixels of imageRect. Each pixel has to be translated into the corresponding position in scale coordinates using the maps. This position can be used to look up a value in a implementation specific way and to map it into a color.

Parameters
xMapX-Scale Map
yMapY-Scale Map
areaRequested area for the image in scale coordinates
imageSizeRequested size of the image
Returns
Rendered image

Implemented in QwtPlotSpectrogram.

◆ setAlpha()

void QwtPlotRasterItem::setAlpha ( int  alpha)

Set an alpha value for the raster data.

Often a plot has several types of raster data organized in layers. ( f.e a geographical map, with weather statistics ). Using setAlpha() raster items can be stacked easily.

The alpha value is a value [0, 255] to control the transparency of the image. 0 represents a fully transparent color, while 255 represents a fully opaque color.

Parameters
alphaAlpha value
  • alpha >= 0
    All alpha values of the pixels returned by renderImage() will be set to alpha, beside those with an alpha value of 0 (invalid pixels).
  • alpha < 0 The alpha values returned by renderImage() are not changed.

The default alpha value is -1.

See also
alpha()

Definition at line 510 of file qwt_plot_rasteritem.cpp.

◆ setCachePolicy()

void QwtPlotRasterItem::setCachePolicy ( QwtPlotRasterItem::CachePolicy  policy)

Change the cache policy

The default policy is NoCache

Parameters
policyCache policy
See also
CachePolicy, cachePolicy()

Definition at line 543 of file qwt_plot_rasteritem.cpp.

◆ setPaintAttribute()

void QwtPlotRasterItem::setPaintAttribute ( PaintAttribute  attribute,
bool  on = true 
)

Specify an attribute how to draw the raster item

Parameters
attributePaint attribute
onOn/Off /sa PaintAttribute, testPaintAttribute()

Definition at line 470 of file qwt_plot_rasteritem.cpp.

◆ testPaintAttribute()

bool QwtPlotRasterItem::testPaintAttribute ( PaintAttribute  attribute) const
Returns
True, when attribute is enabled
See also
PaintAttribute, setPaintAttribute()

Definition at line 482 of file qwt_plot_rasteritem.cpp.