QwtPlotRasterItem(3) Qwt User's Guide QwtPlotRasterItem(3) NAME QwtPlotRasterItem - A class, which displays raster data. SYNOPSIS #include Inherits QwtPlotItem. Inherited by QwtPlotSpectrogram. Public Types enum CachePolicy { NoCache, PaintCache } Cache policy The default policy is NoCache. enum PaintAttribute { PaintInDeviceResolution = 1 } typedef QFlags< PaintAttribute > PaintAttributes Public Member Functions QwtPlotRasterItem (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) CachePolicy cachePolicy () const void invalidateCache () virtual void draw (QPainter *, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &canvasRect) const override Draw the raster data. virtual QRectF pixelHint (const QRectF &) const Pixel hint. virtual QwtInterval interval (Qt::Axis) const virtual QRectF boundingRect () const override Protected Member Functions virtual QImage renderImage (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &area, const QSize &imageSize) const =0 Render an image. 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. 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 Definition at line 37 of file qwt_plot_rasteritem.h. Member Typedef Documentation typedef QFlags QwtPlotRasterItem::PaintAttributes An ORed combination of PaintAttribute values. Definition at line 83 of file qwt_plot_rasteritem.h. 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. Definition at line 44 of file qwt_plot_rasteritem.h. 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. Definition at line 66 of file qwt_plot_rasteritem.h. Member Function Documentation int QwtPlotRasterItem::alpha () const Returns Alpha value of the raster item See also setAlpha() Definition at line 530 of file qwt_plot_rasteritem.cpp. QRectF QwtPlotRasterItem::boundingRect () const [override], [virtual] Returns Bounding rectangle of the data See also QwtPlotRasterItem::interval() Reimplemented from QwtPlotItem. Definition at line 788 of file qwt_plot_rasteritem.cpp. QwtPlotRasterItem::CachePolicy QwtPlotRasterItem::cachePolicy () const Returns Cache policy See also CachePolicy, setCachePolicy() Definition at line 559 of file qwt_plot_rasteritem.cpp. void QwtPlotRasterItem::draw (QPainter * painter, const QwtScaleMap & xMap, const QwtScaleMap & yMap, const QRectF & canvasRect) const [override], [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. Definition at line 614 of file qwt_plot_rasteritem.cpp. QwtScaleMap QwtPlotRasterItem::imageMap (Qt::Orientation orientation, const QwtScaleMap & map, const QRectF & area, const QSize & imageSize, double pixelSize) 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 Definition at line 927 of file qwt_plot_rasteritem.cpp. 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. Definition at line 778 of file qwt_plot_rasteritem.cpp. void QwtPlotRasterItem::invalidateCache () Invalidate the paint cache See also setCachePolicy() Definition at line 568 of file qwt_plot_rasteritem.cpp. 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. Definition at line 601 of file qwt_plot_rasteritem.cpp. virtual QImage QwtPlotRasterItem::renderImage (const QwtScaleMap & xMap, const QwtScaleMap & yMap, const QRectF & area, const QSize & imageSize) const [protected], [pure 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 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() Definition at line 510 of file qwt_plot_rasteritem.cpp. void QwtPlotRasterItem::setCachePolicy (QwtPlotRasterItem::CachePolicy policy) Change the cache policy The default policy is NoCache Parameters policy Cache policy See also CachePolicy, cachePolicy() Definition at line 543 of file qwt_plot_rasteritem.cpp. 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() Definition at line 470 of file qwt_plot_rasteritem.cpp. bool QwtPlotRasterItem::testPaintAttribute (PaintAttribute attribute) const Returns True, when attribute is enabled See also PaintAttribute, setPaintAttribute() Definition at line 482 of file qwt_plot_rasteritem.cpp. Author Generated automatically by Doxygen for Qwt User's Guide from the source code. Version 6.2.0 Sun Jul 18 2021 QwtPlotRasterItem(3)