An overlay for a widget. More...

#include <qwt_widget_overlay.h>

Inheritance diagram for QwtWidgetOverlay:

Classes
class	PrivateData

Public Types
enum	MaskMode { NoMask, MaskHint, AlphaMask }
	Mask mode. More...

enum	RenderMode { AutoRenderMode, CopyAlphaMask, DrawOverlay }
	Render mode. More...

Public Slots
void	updateOverlay ()

Public Member Functions
virtual bool	eventFilter (QObject , QEvent )
	Event filter. More...

MaskMode	maskMode () const

	QwtWidgetOverlay (QWidget *)
	Constructor. More...

RenderMode	renderMode () const

void	setMaskMode (MaskMode)
	Specify how to find the mask for the overlay. More...

void	setRenderMode (RenderMode)

virtual	~QwtWidgetOverlay ()
	Destructor. More...

Protected Member Functions
virtual void	drawOverlay (QPainter *painter) const =0

virtual QRegion	maskHint () const
	Calculate an approximation for the mask. More...

virtual void	paintEvent (QPaintEvent *event)

virtual void	resizeEvent (QResizeEvent *event)

Private Member Functions
void	draw (QPainter *) const

void	updateMask ()

Private Attributes
PrivateData *	d_data

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:

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

See also: QwtPlotCanvas::BackingStore

Definition at line 40 of file qwt_widget_overlay.h.

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.

Definition at line 60 of file qwt_widget_overlay.h.

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.

Definition at line 102 of file qwt_widget_overlay.h.

Constructor & Destructor Documentation

QwtWidgetOverlay::QwtWidgetOverlay ( QWidget * widget )

explicit

Constructor.

Parameters

widget Parent widget, where the overlay is aligned to

Definition at line 114 of file qwt_widget_overlay.cpp.

QwtWidgetOverlay::~QwtWidgetOverlay ( )

virtual

Destructor.

Definition at line 131 of file qwt_widget_overlay.cpp.

Member Function Documentation

void QwtWidgetOverlay::draw ( QPainter * painter ) const

private

Definition at line 307 of file qwt_widget_overlay.cpp.

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

protectedpure virtual

Draw the widget overlay

Parameters

painter Painter

Implemented in QwtPickerTracker, and QwtPickerRubberband.

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()

Definition at line 367 of file qwt_widget_overlay.cpp.

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

Reimplemented in QwtPickerTracker, and QwtPickerRubberband.

Definition at line 351 of file qwt_widget_overlay.cpp.

QwtWidgetOverlay::MaskMode QwtWidgetOverlay::maskMode ( ) const

Returns: Mode how to find the mask for the overlay

See also: setMaskMode()

Definition at line 155 of file qwt_widget_overlay.cpp.

void QwtWidgetOverlay::paintEvent ( QPaintEvent * event )

protectedvirtual

Paint event

Parameters

event Paint event

See also: drawOverlay()

Definition at line 249 of file qwt_widget_overlay.cpp.

QwtWidgetOverlay::RenderMode QwtWidgetOverlay::renderMode ( ) const

Returns: Render mode

See also: RenderMode, setRenderMode()

Definition at line 175 of file qwt_widget_overlay.cpp.

void QwtWidgetOverlay::resizeEvent ( QResizeEvent * event )

protectedvirtual

Resize event

Parameters

event Resize event

Definition at line 300 of file qwt_widget_overlay.cpp.

void QwtWidgetOverlay::setMaskMode ( MaskMode mode )

Specify how to find the mask for the overlay.

Parameters

mode New mode

See also: maskMode()

Definition at line 142 of file qwt_widget_overlay.cpp.

void QwtWidgetOverlay::setRenderMode ( RenderMode mode )

Set the render mode

Parameters

mode	Render mode

See also: RenderMode, renderMode()

Definition at line 166 of file qwt_widget_overlay.cpp.

void QwtWidgetOverlay::updateMask ( )

private

Definition at line 189 of file qwt_widget_overlay.cpp.

void QwtWidgetOverlay::updateOverlay ( )

slot

Recalculate the mask and repaint the overlay

Definition at line 183 of file qwt_widget_overlay.cpp.

Member Data Documentation

PrivateData* QwtWidgetOverlay::d_data

private

Definition at line 146 of file qwt_widget_overlay.h.

The documentation for this class was generated from the following files:

Classes

Public Types

Public Slots

Public Member Functions

Protected Member Functions

Private Member Functions

Private Attributes

Detailed Description

Member Enumeration Documentation

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation