Qwt User's Guide: QwtPlotRasterItem Class Reference

Qwt User's Guide 6.1.2

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QwtPlotRasterItem Class Referenceabstract

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

`#include <qwt_plot_rasteritem.h>`

Inheritance diagram for QwtPlotRasterItem:
[legend]

## Public Types
enum | CachePolicy { NoCache, PaintCache }
| Cache policy The default policy is NoCache. More...
enum | PaintAttribute { PaintInDeviceResolution = 1 }
typedef QFlags< PaintAttribute > | PaintAttributes
| Paint attributes.
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_PlotSVG, Rtti_PlotTradingCurve, Rtti_PlotBarChart, Rtti_PlotMultiBarChart, Rtti_PlotShape, Rtti_PlotTextLabel, Rtti_PlotZone, 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< ItemAttribute > | ItemAttributes
| Plot Item Attributes.
typedef QFlags< ItemInterest > | ItemInterests
| Plot Item Interests.
typedef QFlags< RenderHint > | RenderHints
| Render hints.

## Public Member Functions
| QwtPlotRasterItem (const QString &title=QString::null)
| 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 *p, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &rect) const
| Draw the raster data. More...
virtual QRectF | pixelHint (const QRectF &) const
| Pixel hint. More...
virtual QwtInterval | interval (Qt::Axis) const
virtual QRectF | boundingRect () const
Public Member Functions inherited from QwtPlotItem
| QwtPlotItem (const QwtText &title=QwtText())
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...
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. More...
void | show ()
| Show the item.
void | hide ()
| Hide the item.
virtual void | setVisible (bool)
bool | isVisible () const
void | setAxes (int xAxis, int yAxis)
void | setXAxis (int axis)
int | xAxis () const
| Return xAxis.
void | setYAxis (int axis)
int | yAxis () const
| Return yAxis.
virtual void | itemChanged ()
virtual void | legendChanged ()
virtual void | getCanvasMarginHint (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &canvasSize, 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< QwtLegendData > | legendData () 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

## 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.

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.

## Member Function Documentation

int QwtPlotRasterItem::alpha | ( |  | ) | const

Returns
  Alpha value of the raster item

See Also
  setAlpha()

QRectF QwtPlotRasterItem::boundingRect | ( |  | ) | const
| virtual

Returns
  Bounding rectangle of the data

See Also
  QwtPlotRasterItem::interval()

Reimplemented from QwtPlotItem.

QwtPlotRasterItem::CachePolicy QwtPlotRasterItem::cachePolicy | ( |  | ) | const

Returns
  Cache policy

See Also
  CachePolicy, setCachePolicy()

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

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

  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

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.

void QwtPlotRasterItem::invalidateCache | ( |  | ) |

Invalidate the paint cache

See Also
  setCachePolicy()

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.

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

  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()

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

Change the cache policy

The default policy is NoCache

Parameters

  policy | Cache policy

See Also
  CachePolicy, cachePolicy()

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

Specify an attribute how to draw the raster item

Parameters

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

bool QwtPlotRasterItem::testPaintAttribute | ( | PaintAttribute | attribute | ) | const

Returns
  True, when attribute is enabled

See Also
  PaintAttribute, setPaintAttribute()