QwtPlotRasterItem - A class, which displays raster data.

NAME

QwtPlotRasterItem − A class, which displays raster data.

SYNOPSIS

#include <qwt_plot_rasteritem.h>

Inherits QwtPlotItem.

Inherited by QwtPlotSpectrogram.

Public Types

enum CachePolicy { NoCache, PaintCache }
Cache policy The default policy is NoCache.
enum PaintAttribute { PaintInDeviceResolution = 1 }
typedef QFlags< PaintAttribute > PaintAttributes

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.
enum ItemAttribute { Legend = 0x01, AutoScale = 0x02, Margins = 0x04 }
Plot Item Attributes.
enum ItemInterest { ScaleInterest = 0x01, LegendInterest = 0x02 }
Plot Item Interests.
enum RenderHint { RenderAntialiased = 0x1 }
Render hints.
typedef QFlags< ItemAttribute > ItemAttributes
typedef QFlags< ItemInterest > ItemInterests
typedef QFlags< RenderHint > RenderHints

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.
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.
virtual QRectF pixelHint (const QRectF &) const
Pixel hint.
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.
void detach ()
This method detaches a QwtPlotItem from any QwtPlot it has been associated with.
QwtPlot * plot () const
Return attached plot.
void setTitle (const QString &title)
void setTitle (const QwtText &title)
const QwtText & title () 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.
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.
virtual void updateScaleDiv (const QwtScaleDiv &, const QwtScaleDiv &)
Update the item to changes of the axes scale division.
virtual void updateLegend (const QwtPlotItem *, const QList< QwtLegendData > &)
Update the item to changes of the legend info.
QRectF scaleRect (const QwtScaleMap &, const QwtScaleMap &) const
Calculate the bounding scale rectangle of 2 maps.
QRectF paintRect (const QwtScaleMap &, const QwtScaleMap &) const
Calculate the bounding paint rectangle of 2 maps.
virtual QList< QwtLegendData > legendData () const
Return all information, that is needed to represent the item on the legend.
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.
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.

Protected Member Functions inherited from QwtPlotItem

QwtGraphic defaultIcon (const QBrush &, const QSizeF &) const
Return a default icon from a brush.

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

typedef QFlags<PaintAttribute > QwtPlotRasterItem::PaintAttributes

An ORed combination of PaintAttribute values.

Definition at line 83 of file qwt_plot_rasteritem.h.

Member Enumeration Documentation

enum QwtPlotRasterItem::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.

enum QwtPlotRasterItem::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.

Constructor & Destructor Documentation

QwtPlotRasterItem::QwtPlotRasterItem (const QString & title = QString())[explicit]

Constructor.

Definition at line 434 of file qwt_plot_rasteritem.cpp.

QwtPlotRasterItem::QwtPlotRasterItem (const QwtText & title) [explicit]

Constructor.

Definition at line 441 of file qwt_plot_rasteritem.cpp.

QwtPlotRasterItem::˜QwtPlotRasterItem () [virtual]

Destructor.

Definition at line 448 of file qwt_plot_rasteritem.cpp.

Member Function Documentation

int QwtPlotRasterItem::alpha () const

Returns

Alpha value of the raster item

See also

setAlpha()

Definition at line 530 of file qwt_plot_rasteritem.cpp.

QRectF QwtPlotRasterItem::boundingRect () const [override], [virtual]

Returns

Bounding rectangle of the data

See also

QwtPlotRasterItem::interval()

Reimplemented from QwtPlotItem.

Definition at line 800 of file qwt_plot_rasteritem.cpp.

QwtPlotRasterItem::CachePolicy QwtPlotRasterItem::cachePolicy () const

Returns

Cache policy

See also

CachePolicy, setCachePolicy()

Definition at line 559 of file qwt_plot_rasteritem.cpp.

void QwtPlotRasterItem::draw (QPainter * painter, const QwtScaleMap & xMap,const QwtScaleMap & yMap, const QRectF & canvasRect) const [override],[virtual]

Draw the raster data.

Parameters

painter Painter
xMap X-Scale Map
yMap Y-Scale Map
canvasRect Contents rectangle of the plot canvas

Implements QwtPlotItem.

Reimplemented in QwtPlotSpectrogram.

Definition at line 614 of file qwt_plot_rasteritem.cpp.

QwtScaleMap QwtPlotRasterItem::imageMap (Qt::Orientation orientation, constQwtScaleMap & map, const QRectF & area, const QSize & imageSize, doublepixelSize) const [protected], [virtual]

Calculate a scale map for painting to an image.

Parameters

orientation Orientation, Qt::Horizontal means a X axis
map Scale map for rendering the plot item
area Area to be painted on the image
imageSize Image size
pixelSize Width/Height of a data pixel

Returns

Calculated scale map

Definition at line 939 of file qwt_plot_rasteritem.cpp.

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

axis X, Y, or Z axis

Reimplemented in QwtPlotSpectrogram.

Definition at line 790 of file qwt_plot_rasteritem.cpp.

void QwtPlotRasterItem::invalidateCache ()

Invalidate the paint cache

See also

setCachePolicy()

Definition at line 568 of file qwt_plot_rasteritem.cpp.

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

area In 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.

virtual QImage QwtPlotRasterItem::renderImage (const QwtScaleMap & xMap,const QwtScaleMap & yMap, const QRectF & area, const QSize & imageSize)const [protected], [pure 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

xMap X-Scale Map
yMap Y-Scale Map
area Requested area for the image in scale coordinates
imageSize Requested size of the image

Returns

Rendered image

Implemented in QwtPlotSpectrogram.

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

alpha Alpha 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.

void QwtPlotRasterItem::setCachePolicy (QwtPlotRasterItem::CachePolicypolicy)

Change the cache policy

The default policy is NoCache

Parameters

policy Cache policy

See also

CachePolicy, cachePolicy()

Definition at line 543 of file qwt_plot_rasteritem.cpp.

void QwtPlotRasterItem::setPaintAttribute (PaintAttribute attribute, boolon = true)

Specify an attribute how to draw the raster item

Parameters

attribute Paint attribute
on On/Off /sa PaintAttribute, testPaintAttribute()

Definition at line 470 of file qwt_plot_rasteritem.cpp.

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.

Author

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

Updated 2026-06-01 - jenkler.se | uex.se