Qwt User's Guide  6.0.2
Public Types | Public Member Functions | Protected Member Functions
QwtPlotRasterItem Class Reference

#include <qwt_plot_rasteritem.h>

Inheritance diagram for QwtPlotRasterItem:
Inheritance graph
[legend]

List of all members.

Public Types

enum  CachePolicy {
  NoCache,
  PaintCache
}
enum  PaintAttribute { PaintInDeviceResolution = 1 }
typedef QFlags< PaintAttributePaintAttributes
- Public Types inherited from QwtPlotItem
enum  ItemAttribute {
  Legend = 0x01,
  AutoScale = 0x02
}
typedef QFlags< ItemAttributeItemAttributes
enum  RenderHint { RenderAntialiased = 1 }
typedef QFlags< RenderHintRenderHints
enum  RttiValues {
  Rtti_PlotItem = 0,
  Rtti_PlotGrid,
  Rtti_PlotScale,
  Rtti_PlotMarker,
  Rtti_PlotCurve,
  Rtti_PlotSpectroCurve,
  Rtti_PlotIntervalCurve,
  Rtti_PlotHistogram,
  Rtti_PlotSpectrogram,
  Rtti_PlotSVG,
  Rtti_PlotUserItem = 1000
}

Public Member Functions

 QwtPlotRasterItem (const QString &title=QString::null)
 QwtPlotRasterItem (const QwtText &title)
virtual ~QwtPlotRasterItem ()
int alpha () const
virtual QRectF boundingRect () const
CachePolicy cachePolicy () const
virtual void draw (QPainter *p, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &rect) const
virtual QwtInterval interval (Qt::Axis) const
void invalidateCache ()
virtual QRectF pixelHint (const QRectF &) const
void setAlpha (int alpha)
void setCachePolicy (CachePolicy)
void setPaintAttribute (PaintAttribute, bool on=true)
bool testPaintAttribute (PaintAttribute) const
- Public Member Functions inherited from QwtPlotItem
 QwtPlotItem (const QwtText &title=QwtText())
virtual ~QwtPlotItem ()
void attach (QwtPlot *plot)
void detach ()
void hide ()
bool isVisible () const
virtual void itemChanged ()
virtual QWidget * legendItem () const
QRectF paintRect (const QwtScaleMap &, const QwtScaleMap &) const
QwtPlotplot () const
virtual int rtti () const
QRectF scaleRect (const QwtScaleMap &, const QwtScaleMap &) const
void setAxes (int xAxis, int yAxis)
void setItemAttribute (ItemAttribute, bool on=true)
void setRenderHint (RenderHint, bool on=true)
void setTitle (const QString &title)
void setTitle (const QwtText &title)
virtual void setVisible (bool)
void setXAxis (int axis)
void setYAxis (int axis)
void setZ (double z)
void show ()
bool testItemAttribute (ItemAttribute) const
bool testRenderHint (RenderHint) const
const QwtTexttitle () const
virtual void updateLegend (QwtLegend *) const
virtual void updateScaleDiv (const QwtScaleDiv &, const QwtScaleDiv &)
int xAxis () const
int yAxis () const
double z () const
- Public Member Functions inherited from QwtLegendItemManager
 QwtLegendItemManager ()
virtual ~QwtLegendItemManager ()
virtual void drawLegendIdentifier (QPainter *, const QRectF &) const

Protected Member Functions

virtual QwtScaleMap imageMap (Qt::Orientation, const QwtScaleMap &map, const QRectF &area, const QSize &imageSize, double pixelSize) const
virtual QImage renderImage (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &area, const QSize &imageSize) const =0

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

  • NoCache
    renderImage() is called, whenever 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 only useful for improving the performance of hide/show operations. All other situations are already handled by the plot canvas cache.

The default policy is NoCache

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 rect 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:
painterPainter
xMapX-Scale Map
yMapY-Scale Map
canvasRectContents rect 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:
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
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.

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 neighboured 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.

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

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

Change the cache policy

The default policy is NoCache

Parameters:
policyCache policy
See also:
CachePolicy, cachePolicy()
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()
bool QwtPlotRasterItem::testPaintAttribute ( PaintAttribute  attribute) const

Return the current paint attributes.

See also:
PaintAttribute, setPaintAttribute()