QwtWidgetOverlay类 参考

An overlay for a widget 更多...

#include <qwt_widget_overlay.h>

类 QwtWidgetOverlay 继承关系图:

类
class	PrivateData

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

Public 槽
void	updateOverlay ()
	Recalculate the mask and repaint the overlay

Public 成员函数
	QwtWidgetOverlay (QWidget *)
	Constructor
void	setMaskMode (MaskMode)
	Specify how to find the mask for the overlay
MaskMode	maskMode () const
void	setRenderMode (RenderMode)
	Set the render mode
RenderMode	renderMode () const
virtual bool	eventFilter (QObject *, QEvent *) override
	Event filter

Protected 成员函数
virtual void	paintEvent (QPaintEvent *) override
	Paint event
virtual void	resizeEvent (QResizeEvent *) override
	Resize event
virtual QRegion	maskHint () const
	Calculate an approximation for the mask
virtual void	drawOverlay (QPainter *painter) const =0
	Draw the widget overlay

详细描述

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.

参见

QwtPlotCanvas::BackingStore

成员枚举类型说明

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.

参见

setMaskMode(), maskMode()

枚举值
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.

注解

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

枚举值
AutoRenderMode	Copy the buffer, when using the raster paint engine.
CopyAlphaMask	Always copy the buffer
DrawOverlay	Never copy the buffer

构造及析构函数说明

QwtWidgetOverlay()

QwtWidgetOverlay::QwtWidgetOverlay ( QWidget *  widget )

explicit

Constructor

参数

widget

Parent widget, where the overlay is aligned to

Destructor

成员函数说明

drawOverlay()

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

protectedpure virtual

Draw the widget overlay

参数

painter

Painter

在 QwtFigureWidgetOverlay 内被实现.

eventFilter()

bool QwtWidgetOverlay::eventFilter ( QObject *  object, QEvent *  event  )

overridevirtual

Event filter

Resize the overlay according to the size of the parent widget.

参数

[in]	object	Object to be filtered
[in]	event	Event

返回

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.

返回

Hint for the mask

被 QwtFigureWidgetOverlay 重载.

maskMode()

QwtWidgetOverlay::MaskMode QwtWidgetOverlay::maskMode

(

)

const

返回

Mode how to find the mask for the overlay

参见

setMaskMode()

paintEvent()

void QwtWidgetOverlay::paintEvent ( QPaintEvent *  event )

overrideprotectedvirtual

Paint event

参数

event

Paint event

参见

drawOverlay()

renderMode()

QwtWidgetOverlay::RenderMode QwtWidgetOverlay::renderMode

(

)

const

返回

Render mode

参见

RenderMode, setRenderMode()

resizeEvent()

void QwtWidgetOverlay::resizeEvent ( QResizeEvent *  event )

overrideprotectedvirtual

Resize event

参数

event

Resize event

setMaskMode()

void QwtWidgetOverlay::setMaskMode

(

MaskMode

mode

)

Specify how to find the mask for the overlay

参数

mode

New mode

参见

maskMode()

setRenderMode()

void QwtWidgetOverlay::setRenderMode

(

RenderMode

mode

)

Set the render mode

参数

[in]

mode

Render mode

参见

RenderMode, renderMode()

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该类的文档由以下文件生成:

• /home/runner/work/QWT/QWT/src/plot/qwt_widget_overlay.h
• /home/runner/work/QWT/QWT/src/plot/qwt_widget_overlay.cpp