QGraphicsEffect 类

QGraphicsEffect 类是用于所有图形效果的基类。 更多...

头：	#include <QGraphicsEffect>
qmake:	QT += widgets
Since:	Qt 4.6
继承：	QObject
继承者：	QGraphicsBlurEffect , QGraphicsColorizeEffect , QGraphicsDropShadowEffect ，和 QGraphicsOpacityEffect

该类在 Qt 4.6 引入。

• 所有成员列表，包括继承成员

公共类型

enum	ChangeFlag { SourceAttached, SourceDetached, SourceBoundingRectChanged, SourceInvalidated }
flags	ChangeFlags
enum	PixmapPadMode { NoPad, PadToTransparentBorder, PadToEffectiveBoundingRect }

特性

• enabled : bool

公共函数

	QGraphicsEffect (QObject * parent = nullptr)
virtual	~QGraphicsEffect ()
QRectF	boundingRect () const
virtual QRectF	boundingRectFor (const QRectF & rect ) const
bool	isEnabled () const

公共槽

void	setEnabled (bool enable )
void	update ()

信号

void	enabledChanged (bool enabled )

保护函数

virtual void	draw (QPainter * painter ) = 0
void	drawSource (QPainter * painter )
QRectF	sourceBoundingRect (Qt::CoordinateSystem system = Qt::LogicalCoordinates) const
virtual void	sourceChanged (QGraphicsEffect::ChangeFlags flags )
bool	sourceIsPixmap () const
QPixmap	sourcePixmap (Qt::CoordinateSystem system = Qt::LogicalCoordinates, QPoint * offset = nullptr, QGraphicsEffect::PixmapPadMode mode = PadToEffectiveBoundingRect) const
void	updateBoundingRect ()

详细描述

效果更改元素的外观是通过挂钩到渲染管道并运转于源 (如 QGraphicsPixmapItem ) 和目的地设备 (如 QGraphicsView 的视口)。可以禁用效果通过调用 setEnabled (false)。若效果被禁用，则直接渲染源。

要将视觉效果添加到 QGraphicsItem ，例如，可以使用标准效果之一，或通过创建 QGraphicsEffect 子类来创建自己的效果。然后可以在项中安装效果使用 QGraphicsItem::setGraphicsEffect ().

Qt 提供下列标准效果：

• QGraphicsBlurEffect - 按给定半径模糊项
• QGraphicsDropShadowEffect - 渲染项后投影
• QGraphicsColorizeEffect - 以任意给定颜色着色渲染项
• QGraphicsOpacityEffect - 按不透明度渲染项

For more information on how to use each effect, refer to the specific effect's documentation.

To create your own custom effect, create a subclass of QGraphicsEffect (or any other existing effects) and reimplement the virtual function draw (). This function is called whenever the effect needs to redraw. The draw () function takes the painter with which to draw as an argument. For more information, refer to the documentation for draw (). In the draw () function you can call sourcePixmap () to get a pixmap of the graphics effect source which you can then process.

If your effect changes, use update () to request for a redraw. If your custom effect changes the bounding rectangle of the source, e.g., a radial glow effect may need to apply an extra margin, you can reimplement the virtual boundingRectFor () function, and call updateBoundingRect () to notify the framework whenever this rectangle changes. The virtual sourceChanged () function is called to notify the effects that the source has changed in some way - e.g., if the source is a QGraphicsRectItem and its rectangle parameters have changed.

另请参阅 QGraphicsItem::setGraphicsEffect () 和 QWidget::setGraphicsEffect ().

成员类型文档编制

enum QGraphicsEffect:: ChangeFlag
flags QGraphicsEffect:: ChangeFlags

This enum describes what has changed in QGraphicsEffectSource.

常量	值	描述
QGraphicsEffect::SourceAttached	0x1	The effect is installed on a source.
QGraphicsEffect::SourceDetached	0x2	The effect is uninstalled on a source.
QGraphicsEffect::SourceBoundingRectChanged	0x4	The bounding rect of the source has changed.
QGraphicsEffect::SourceInvalidated	0x8	The visual appearance of the source has changed.

ChangeFlags 类型是 typedef 对于 QFlags <ChangeFlag>。它存储 ChangeFlag 值的 OR 组合。

enum QGraphicsEffect:: PixmapPadMode

This enum describes how the pixmap returned from sourcePixmap should be padded.

常量	值	描述
QGraphicsEffect::NoPad	0	The pixmap should not receive any additional padding.
QGraphicsEffect::PadToTransparentBorder	1	The pixmap should be padded to ensure it has a completely transparent border.
QGraphicsEffect::PadToEffectiveBoundingRect	2	The pixmap should be padded to match the effective bounding rectangle of the effect.

特性文档编制

enabled : bool

This property holds whether the effect is enabled or not.

If an effect is disabled, the source will be rendered with as normal, with no interference from the effect. If the effect is enabled, the source will be rendered with the effect applied.

This property is enabled by default.

Using this property, you can disable certain effects on slow platforms, in order to ensure that the user interface is responsive.

访问函数：

bool	isEnabled () const
void	setEnabled (bool enable )

通知程序信号：

void	enabledChanged (bool enabled )

成员函数文档编制

QGraphicsEffect:: QGraphicsEffect ( QObject * parent = nullptr)

Constructs a new QGraphicsEffect instance having the specified parent .

[signal] void QGraphicsEffect:: enabledChanged ( bool enabled )

This signal is emitted whenever the effect is enabled or disabled. The enabled parameter holds the effects's new enabled state.

注意： 通知程序信号对于特性 enabled .

另请参阅 isEnabled ().

[slot] void QGraphicsEffect:: update ()

Schedules a redraw of the effect. Call this function whenever the effect needs to be redrawn. This function does not trigger a redraw of the source.

另请参阅 updateBoundingRect ().

[虚拟] QGraphicsEffect:: ~QGraphicsEffect ()

Removes the effect from the source, and destroys the graphics effect.

QRectF QGraphicsEffect:: boundingRect () const

Returns the effective bounding rectangle for this effect, i.e., the bounding rectangle of the source in device coordinates, adjusted by any margins applied by the effect itself.

另请参阅 boundingRectFor () 和 updateBoundingRect ().

[虚拟] QRectF QGraphicsEffect:: boundingRectFor (const QRectF & rect ) const

Returns the effective bounding rectangle for this effect, given the provided rect in the device coordinates. When writing you own custom effect, you must call updateBoundingRect () whenever any parameters are changed that may cause this this function to return a different value.

另请参阅 sourceBoundingRect ().

[pure virtual protected] void QGraphicsEffect:: draw ( QPainter * painter )

This pure virtual function draws the effect and is called whenever the source needs to be drawn.

Reimplement this function in a QGraphicsEffect subclass to provide the effect's drawing implementation, using painter .

例如：

MyGraphicsEffect::draw(QPainter *painter)
{
    ...
    QPoint offset;
    if (sourceIsPixmap()) {
        // No point in drawing in device coordinates (pixmap will be scaled anyways).
        const QPixmap pixmap = sourcePixmap(Qt::LogicalCoordinates, &offset);
        ...
        painter->drawPixmap(offset, pixmap);
    } else {
        // Draw pixmap in device coordinates to avoid pixmap scaling;
        const QPixmap pixmap = sourcePixmap(Qt::DeviceCoordinates, &offset);
        painter->setWorldTransform(QTransform());
        ...
        painter->drawPixmap(offset, pixmap);
    }
    ...
}
					

This function should not be called explicitly by the user, since it is meant for reimplementation purposes only.

[protected] void QGraphicsEffect:: drawSource ( QPainter * painter )

Draws the source directly using the given painter .

This function should only be called from QGraphicsEffect::draw ().

例如：

MyGraphicsOpacityEffect::draw(QPainter *painter)
{
    // Fully opaque; draw directly without going through a pixmap.
    if (qFuzzyCompare(m_opacity, 1)) {
        drawSource(painter);
        return;
    }
    ...
}
					

另请参阅 QGraphicsEffect::draw ().

[protected] QRectF QGraphicsEffect:: sourceBoundingRect ( Qt::CoordinateSystem system = Qt::LogicalCoordinates) const

Returns the bounding rectangle of the source mapped to the given system .

调用此函数采用 Qt::DeviceCoordinates outside of QGraphicsEffect::draw () will give undefined results, as there is no device context available.

另请参阅 draw ().

[virtual protected] void QGraphicsEffect:: sourceChanged ( QGraphicsEffect::ChangeFlags flags )

此虚函数被调用由 QGraphicsEffect to notify the effect that the source has changed. If the effect applies any cache, then this cache must be purged in order to reflect the new appearance of the source.

The flags describes what has changed.

[protected] bool QGraphicsEffect:: sourceIsPixmap () const

返回 true if the source effectively is a pixmap, e.g., a QGraphicsPixmapItem .

This function is useful for optimization purposes. For instance, there's no point in drawing the source in device coordinates to avoid pixmap scaling if this function returns true - the source pixmap will be scaled anyways.

[protected] QPixmap QGraphicsEffect:: sourcePixmap ( Qt::CoordinateSystem system = Qt::LogicalCoordinates, QPoint * offset = nullptr, QGraphicsEffect::PixmapPadMode mode = PadToEffectiveBoundingRect) const

Returns a pixmap with the source painted into it.

The system specifies which coordinate system to be used for the source. The optional offset parameter returns the offset where the pixmap should be painted at using the current painter. For control on how the pixmap is padded use the mode 参数。

The returned pixmap is clipped to the current painter's device rectangle when system is Qt::DeviceCoordinates .

调用此函数采用 Qt::DeviceCoordinates outside of QGraphicsEffect::draw () will give undefined results, as there is no device context available.

另请参阅 draw () 和 boundingRect ().

[protected] void QGraphicsEffect:: updateBoundingRect ()

This function notifies the effect framework when the effect's bounding rectangle has changed. As a custom effect author, you must call this function whenever you change any parameters that will cause the virtual boundingRectFor () function to return a different value.

This function will call update () 若这是必要的。

另请参阅 boundingRectFor (), boundingRect ()，和 sourceBoundingRect ().

内容

• 公共类型

• 特性

• 公共函数

• 公共槽

• 信号

• 保护函数

• 详细描述