NAME

       QwtWidgetOverlay -

       An overlay for a widget.

SYNOPSIS

       #include <qwt_widget_overlay.h>

       Inherits QWidget.

       Inherited by QwtPickerRubberband, and QwtPickerTracker.

   Public Types
       enum MaskMode { NoMask, MaskHint, AlphaMask }
           Mask mode.
       enum RenderMode { AutoRenderMode, CopyAlphaMask, DrawOverlay }
           Render mode.

   Public Member Functions
       QwtWidgetOverlay (QWidget *)
           Constructor.
       virtual ~QwtWidgetOverlay ()
           Destructor.
       void setMaskMode (MaskMode)
           Specify how to find the mask for the overlay.
       MaskMode maskMode () const
       void setRenderMode (RenderMode)
       RenderMode renderMode () const
       void updateOverlay ()
       virtual bool eventFilter (QObject *, QEvent *)
           Event filter.

   Protected Member Functions
       virtual void paintEvent (QPaintEvent *event)
       virtual void resizeEvent (QResizeEvent *event)
       virtual QRegion maskHint () const
           Calculate an approximation for the mask.
       virtual void drawOverlay (QPainter *painter) const =0

Detailed Description

       An overlay for a widget.

       The main use case of an widget overlay is to avoid heavy repaint operation of the widget below.

       F.e. in combination with the plot canvas an overlay avoid replots as the content of the canvas can be
       restored from its backing store.

       QwtWidgetOverlay is an abstract base class. Deriving classes are supposed to reimplement the following
       methods:

       • drawOverlay()

       • maskHint()

       Internally QwtPlotPicker uses overlays for displaying the rubber band and the tracker text.

       See Also:
           QwtPlotCanvas::BackingStore

Member Enumeration Documentation

   enum QwtWidgetOverlay::MaskMode
       Mask mode. When using masks the widget below gets paint events for the masked regions of the overlay
       only. Otherwise Qt triggers full repaints. On less powerful hardware ( f.e embedded systems ) - or when
       using the raster paint engine on a remote desktop - bit blitting is a noticeable operation, that needs to
       be avoided.

       If and how to mask depends on how expensive the calculation of the mask is and how many pixels can be
       excluded by the mask.

       The default setting is MaskHint.

       See Also:
           setMaskMode(), maskMode()

       Enumerator

       NoMask Don't use a mask.

       MaskHint
              Use maskHint() as mask. For many situations a fast approximation is good enough and it is not
              necessary to build a more detailed mask ( f.e the bounding rectangle of a text ).

       AlphaMask
              Calculate a mask by checking the alpha values. Sometimes it is not possible to give a fast
              approximation and the mask needs to be calculated by drawing the overlay and testing the result.

       When a valid maskHint() is available only pixels inside this approximation are checked.

   enum QwtWidgetOverlay::RenderMode
       Render mode. For calculating the alpha mask the overlay has already been painted to a temporary QImage.
       Instead of rendering the overlay twice this buffer can be copied for drawing the overlay.

       On graphic systems using the raster paint engine ( QWS, Windows ) it means usually copying some memory
       only. On X11 it results in an expensive operation building a pixmap and for simple overlays it might not
       be recommended.

       Note:
           The render mode has no effect, when maskMode() != AlphaMask.

       Enumerator

       AutoRenderMode
              Copy the buffer, when using the raster paint engine.

       CopyAlphaMask
              Always copy the buffer.

       DrawOverlay
              Never copy the buffer.

Constructor & Destructor Documentation

   QwtWidgetOverlay::QwtWidgetOverlay (QWidget *widget)
       Constructor.

       Parameters:
           widget Parent widget, where the overlay is aligned to

Member Function Documentation

   virtual void QwtWidgetOverlay::drawOverlay (QPainter *painter) const [protected],  [pure virtual]
       Draw the widget overlay

       Parameters:
           painter Painter

   bool QwtWidgetOverlay::eventFilter (QObject *object, QEvent *event) [virtual]
       Event filter. Resize the overlay according to the size of the parent widget.

       Parameters:
           object Object to be filtered
           event Event

       Returns:
           See QObject::eventFilter()

   QRegion QwtWidgetOverlay::maskHint () const [protected],  [virtual]
       Calculate an approximation for the mask.

       • MaskHint The hint is used as mask.

       • AlphaMask The hint is used to speed up the algorithm for calculating a mask from non transparent pixels

       • NoMask The hint is unused.

       The default implementation returns an invalid region indicating no hint.

       Returns:
           Hint for the mask

   QwtWidgetOverlay::MaskMode QwtWidgetOverlay::maskMode () const
       Returns:
           Mode how to find the mask for the overlay

       See Also:
           setMaskMode()

   void QwtWidgetOverlay::paintEvent (QPaintEvent *event) [protected],  [virtual]
       Paint event

       Parameters:
           event Paint event

       See Also:
           drawOverlay()

   QwtWidgetOverlay::RenderMode QwtWidgetOverlay::renderMode () const
       Returns:
           Render mode

       See Also:
           RenderMode, setRenderMode()

   void QwtWidgetOverlay::resizeEvent (QResizeEvent *event) [protected],  [virtual]
       Resize event

       Parameters:
           event Resize event

   void QwtWidgetOverlay::setMaskMode (MaskModemode)
       Specify how to find the mask for the overlay.

       Parameters:
           mode New mode

       See Also:
           maskMode()

   void QwtWidgetOverlay::setRenderMode (RenderModemode)
       Set the render mode

       Parameters:
           mode Render mode

       See Also:
           RenderMode, renderMode()

   void QwtWidgetOverlay::updateOverlay ()
       Recalculate the mask and repaint the overlay

Author

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