QwtPlotRasterItem - A class, which displays raster data.

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

Version 6.1.4                                    Wed Jan 2 2019                             QwtPlotRasterItem(3)

       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.

       Seealso:QwtPlotSpectrogram

enumQwtPlotRasterItem::CachePolicy
       Cache policy The default policy is NoCache.

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

       PaintCacherenderImage()  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.

   enumQwtPlotRasterItem::PaintAttribute
       Attributes to modify the drawing algorithm.

       Seealso:setPaintAttribute(), testPaintAttribute()EnumeratorPaintInDeviceResolution
              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.

intQwtPlotRasterItem::alpha()constReturns:
           Alpha value of the raster item

       Seealso:setAlpha()QRectFQwtPlotRasterItem::boundingRect()const[virtual]Returns:
           Bounding rectangle of the data

       Seealso:QwtPlotRasterItem::interval()

       Reimplemented from QwtPlotItem.

   QwtPlotRasterItem::CachePolicyQwtPlotRasterItem::cachePolicy()constReturns:
           Cache policy

       Seealso:CachePolicy, setCachePolicy()voidQwtPlotRasterItem::draw(QPainter*painter,constQwtScaleMap&xMap,constQwtScaleMap&yMap,constQRectF&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.

   QwtScaleMapQwtPlotRasterItem::imageMap(Qt::Orientationorientation,constQwtScaleMap&map,constQRectF&area,constQSize&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

   QwtIntervalQwtPlotRasterItem::interval(Qt::Axisaxis)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.

   voidQwtPlotRasterItem::invalidateCache()
       Invalidate the paint cache

       Seealso:setCachePolicy()QRectFQwtPlotRasterItem::pixelHint(constQRectF&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

       Seealso:
           render(), renderImage()

       Reimplemented in QwtPlotSpectrogram.

   virtualQImageQwtPlotRasterItem::renderImage(constQwtScaleMap&xMap,constQwtScaleMap&yMap,constQRectF&area,constQSize&imageSize)const[protected],[purevirtual]
       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.

   voidQwtPlotRasterItem::setAlpha(intalpha)
       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.

       Seealso:alpha()voidQwtPlotRasterItem::setCachePolicy(QwtPlotRasterItem::CachePolicypolicy)
       Change the cache policy

       The default policy is NoCache

       Parameters:policy Cache policy

       Seealso:CachePolicy, cachePolicy()voidQwtPlotRasterItem::setPaintAttribute(PaintAttributeattribute,boolon=true)
       Specify an attribute how to draw the raster item

       Parameters:attribute Paint attribute
           on On/Off /sa PaintAttribute, testPaintAttribute()boolQwtPlotRasterItem::testPaintAttribute(PaintAttributeattribute)constReturns:
           True, when attribute is enabled

       Seealso:PaintAttribute, setPaintAttribute()

       QwtPlotRasterItem - A class, which displays raster data.

       #include <qwt_plot_rasteritem.h>

       Inherits QwtPlotItem.

       Inherited by QwtPlotSpectrogram.

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

   PublicMemberFunctionsQwtPlotRasterItem (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)
       CachePolicycachePolicy () const
       void invalidateCache ()
       virtual void draw (QPainter *, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF
           &canvasRect) const
           Draw the raster data.
       virtual QRectF pixelHint (const QRectF &) const
           Pixel hint.
       virtual QwtIntervalinterval (Qt::Axis) const
       virtual QRectF boundingRect () const

   ProtectedMemberFunctions
       virtual QImage renderImage (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &area, const
           QSize &imageSize) const =0
           Render an image.
       virtual QwtScaleMapimageMap (Qt::Orientation, const QwtScaleMap &map, const QRectF &area, const QSize
           &imageSize, double pixelSize) const
           Calculate a scale map for painting to an image.