NAME

       QwtPlotRasterItem -

SYNOPSIS

       #include <qwt_plot_rasteritem.h>

       Inherits QwtPlotItem.

       Inherited by QwtPlotSpectrogram.

   Public Types
       enum CachePolicy { NoCache, PaintCache, ScreenCache }

   Public Member Functions
       QwtPlotRasterItem (const QString &title=QString::null)
       QwtPlotRasterItem (const QwtText &title)
       virtual ~QwtPlotRasterItem ()
       int alpha () const
       CachePolicy cachePolicy () const
       virtual void draw (QPainter *p, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const
           QRect &rect) const
       void invalidateCache ()
       virtual QSize rasterHint (const QwtDoubleRect &) const
       void setAlpha (int alpha)
       void setCachePolicy (CachePolicy)

   Protected Member Functions
       virtual QImage renderImage (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const
           QwtDoubleRect &area) 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

   enum QwtPlotRasterItem::CachePolicy
       • 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.

       • ScreenCache
          The screen cache is an image in size of the screen. As long as the scales don't change
         the target image is scaled from the cache. This might improve the performance when
         resizing the plot widget, but suffers from scaling effects.

       The default policy is NoCache

Member Function Documentation

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

       See also:
           setAlpha()

   QwtPlotRasterItem::CachePolicy QwtPlotRasterItem::cachePolicy () const
       Returns:
           Cache policy

       See also:
           CachePolicy, setCachePolicy()

   void QwtPlotRasterItem::draw (QPainter *painter, const QwtScaleMap &xMap, const QwtScaleMap
       &yMap, const QRect &canvasRect) const [virtual]
       Draw the raster data. Parameters:
           painter Painter
           xMap X-Scale Map
           yMap Y-Scale Map
           canvasRect Contents rect of the plot canvas

       Implements QwtPlotItem.

       Reimplemented in QwtPlotSpectrogram.

   void QwtPlotRasterItem::invalidateCache ()
       Invalidate the paint cache

       See also:
           setCachePolicy()

   QSize QwtPlotRasterItem::rasterHint (const QwtDoubleRect &) const [virtual]
       Returns the recommended raster for a given rect. F.e the raster hint can be used to limit
       the resolution of the image that is rendered.

       The default implementation returns an invalid size (QSize()), what means: no hint.

       Reimplemented in QwtPlotSpectrogram.

   virtual QImage QwtPlotRasterItem::renderImage (const QwtScaleMap &xMap, const QwtScaleMap
       &yMap, const QwtDoubleRect &area) const [protected],  [pure virtual]
       Renders an image for an area

       The format of the image must be QImage::Format_Indexed8, QImage::Format_RGB32 or
       QImage::Format_ARGB32

       Parameters:
           xMap Maps x-values into pixel coordinates.
           yMap Maps y-values into pixel coordinates.
           area Requested area for the image in scale coordinates

       Implemented in QwtPlotSpectrogram.

   void QwtPlotRasterItem::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.

       See also:
           alpha()

   void QwtPlotRasterItem::setCachePolicy (QwtPlotRasterItem::CachePolicypolicy)
       Change the cache policy

       The default policy is NoCache

       Parameters:
           policy Cache policy

       See also:
           CachePolicy, cachePolicy()

Author

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