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QwtPlotRasterItem(3)           Qwt User's Guide           QwtPlotRasterItem(3)

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
       o NoCache
          renderImage() is called, whenever the item has to be repainted

       o 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.

       o 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

       o 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).

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

Version 5.2.3                   Tue Nov 20 2012           QwtPlotRasterItem(3)