QGraphicsEffect Class Reference
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QtGui

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The QGraphicsEffect class is the base class for all graphics effects. 更多...

继承 QObject .

Inherited by QGraphicsBlurEffect , QGraphicsColorizeEffect , QGraphicsDropShadowEffect and QGraphicsOpacityEffect .

类型

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

方法

__init__ ( self , QObject parent = None)
QRectF boundingRect ( self )
QRectF boundingRectFor ( self , QRectF sourceRect )
draw ( self , QPainter painter )
drawSource ( self , QPainter painter )
bool isEnabled ( self )
setEnabled ( self , bool enable )
QRectF sourceBoundingRect ( self , Qt.CoordinateSystem system = Qt.LogicalCoordinates)
sourceChanged ( self , ChangeFlags flags )
bool sourceIsPixmap ( self )
(QPixmap, QPoint offset ) sourcePixmap ( self , Qt.CoordinateSystem system = Qt.LogicalCoordinates, PixmapPadMode mode = QGraphicsEffect.PadToEffectiveBoundingRect)
update ( self )
updateBoundingRect ( self )

Qt Signals

void enabledChanged (bool)

详细描述

The QGraphicsEffect class is the base class for all graphics effects.

Effects alter the appearance of elements by hooking into the rendering pipeline and operating between the source (e.g., a QGraphicsPixmapItem ) and the destination device (e.g., QGraphicsView 's viewport). Effects can be disabled by calling setEnabled(false). If effects are disabled, the source is rendered directly.

To add a visual effect to a QGraphicsItem , for example, you can use one of the standard effects, or alternately, create your own effect by creating a subclass of QGraphicsEffect. The effect can then be installed on the item using QGraphicsItem.setGraphicsEffect ().

Qt provides the following standard effects:

QGraphicsBlurEffect - blurs the item by a given radius
QGraphicsDropShadowEffect - renders a dropshadow behind the item
QGraphicsColorizeEffect - renders the item in shades of any given color
QGraphicsOpacityEffect - renders the item with an opacity

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 documenation for draw (). In the draw () function you can call sourcePixmap () 到 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.

类型文档编制

QGraphicsEffect.ChangeFlag

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 改变。
`QGraphicsEffect.SourceInvalidated`	`0x8`	The visual appearance of the source has 改变。

The ChangeFlags type is a typedef for QFlags <ChangeFlag>. It stores an OR combination of ChangeFlag values.

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.

方法文档编制

QGraphicsEffect.init ( self , QObject parent = None)

parent argument, if not None, causes self to be owned by Qt instead of PyQt.

构造新 QGraphicsEffect instance having the specified parent .

QRectF QGraphicsEffect.boundingRect ( self )

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 ().

QRectF QGraphicsEffect.boundingRectFor ( self , QRectF sourceRect )

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 ().

QGraphicsEffect.draw ( self , QPainter painter )

This method is abstract and should be reimplemented in any sub-class.

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.

QGraphicsEffect.drawSource ( self , 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 ().

bool QGraphicsEffect.isEnabled ( self )

QGraphicsEffect.setEnabled ( self , bool enable )

This method is also a Qt slot with the C++ signature void setEnabled(bool) .

QRectF QGraphicsEffect.sourceBoundingRect ( self , Qt.CoordinateSystem system = Qt.LogicalCoordinates)

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 ().

QGraphicsEffect.sourceChanged ( self , ChangeFlags flags )

此虚拟函数被调用由 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.

flags describes what has changed.

bool QGraphicsEffect.sourceIsPixmap ( self )

Returns 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.

( QPixmap , QPoint offset ) QGraphicsEffect.sourcePixmap ( self , Qt.CoordinateSystem system = Qt.LogicalCoordinates, PixmapPadMode mode = QGraphicsEffect.PadToEffectiveBoundingRect)

Returns a pixmap with the source painted into it.

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 () and boundingRect ().

QGraphicsEffect.update ( self )

This method is also a Qt slot with the C++ signature void 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 ().

QGraphicsEffect.updateBoundingRect ( self )

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 () if this is necessary.

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

Qt Signal Documentation

void enabledChanged (bool)

This is the default overload of this signal.

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

另请参阅 isEnabled ().

QGraphicsEffect Class Reference [ QtGui module]

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方法