QwtWidgetOverlay Class Reference

An overlay for a widget. More...

#include <qwt_widget_overlay.h>

Inheritance diagram for QwtWidgetOverlay:

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

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

Protected Member Functions
virtual void	paintEvent (QPaintEvent *event)
virtual void	resizeEvent (QResizeEvent *event)
virtual QRegion	maskHint () const
	Calculate an approximation for the mask. More...
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

MaskMode

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.

RenderMode

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::QwtWidgetOverlay

(

QWidget *

widget

)

Constructor.

Parameters

widget

Parent widget, where the overlay is aligned to

Member Function Documentation

drawOverlay()

virtual void QwtWidgetOverlay::drawOverlay ( QPainter *  painter ) const

protectedpure virtual

Draw the widget overlay

Parameters

painter

Painter

eventFilter()

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()

maskHint()

QRegion QwtWidgetOverlay::maskHint ( ) const

protectedvirtual

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

maskMode()

QwtWidgetOverlay::MaskMode QwtWidgetOverlay::maskMode

(

)

const

Returns

Mode how to find the mask for the overlay

See also

setMaskMode()

paintEvent()

void QwtWidgetOverlay::paintEvent ( QPaintEvent *  event )

protectedvirtual

Paint event

Parameters

event

Paint event

See also

drawOverlay()

renderMode()

QwtWidgetOverlay::RenderMode QwtWidgetOverlay::renderMode

(

)

const

Returns

Render mode

See also

RenderMode, setRenderMode()

resizeEvent()

void QwtWidgetOverlay::resizeEvent ( QResizeEvent *  event )

protectedvirtual

Resize event

Parameters

event

Resize event

setMaskMode()

void QwtWidgetOverlay::setMaskMode

(

MaskMode

mode

)

Specify how to find the mask for the overlay.

Parameters

mode

New mode

See also

maskMode()

setRenderMode()

void QwtWidgetOverlay::setRenderMode

(

RenderMode

mode

)

Set the render mode

Parameters

mode	Render mode

See also

RenderMode, renderMode()

updateOverlay()

void QwtWidgetOverlay::updateOverlay

(

)

Recalculate the mask and repaint the overlay