QGraphicsEffect Class Reference

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

  1. #include <QGraphicsEffect>

Inherits: QObject.

Inherited by: QGraphicsBlurEffect, QGraphicsColorizeEffect, QGraphicsDropShadowEffect, and QGraphicsOpacityEffect.

This class was introduced in Qt 4.6.

Detailed Description

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:

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() 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.

See also QGraphicsItem::setGraphicsEffect() and QWidget::setGraphicsEffect().

Public Types

Toggle detailsenum QGraphicsEffect::

ChangeFlagChangeFlag { SourceAttached , SourceDetached , SourceBoundingRectChanged , SourceInvalidated 0x8 ...} { SourceAttached , SourceDetached , SourceBoundingRectChanged , SourceInvalidated 0x8 }

This enum describes what has changed in QGraphicsEffectSource.

ConstantValueDescription
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.

Look up this member in the source code.

Toggle detailsenum QGraphicsEffect::

PixmapPadModePixmapPadMode { NoPad , PadToTransparentBorder , PadToEffectiveBoundingRect 2 ...} { NoPad , PadToTransparentBorder , PadToEffectiveBoundingRect 2 }

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

ConstantValueDescription
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.

Look up this member in the source code.

    Properties

    Toggle detailsenabledenabled : 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.

    Access functions:

    Look up this member in the source code.

      Public Functions

      Toggle details QGraphicsEffect

      QGraphicsEffectQGraphicsEffect ( QObject *parent=0 ) ( QObject *parent=0 )

      Constructs a new QGraphicsEffect instance having the specified parent.

      Look up this member in the source code.

      Toggle details QGraphicsEffect

      ~QGraphicsEffect~QGraphicsEffect () () [virtual]

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

      Look up this member in the source code.

      Toggle details QRectF QGraphicsEffect

      boundingRectboundingRect () ()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.

      See also boundingRectFor() and updateBoundingRect().

      Look up this member in the source code.

      Toggle details QRectF QGraphicsEffect

      boundingRectForboundingRectFor ( const QRectF &rect ) ( const QRectF &rect )const [virtual]

      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.

      See also sourceBoundingRect().

      Look up this member in the source code.

      Toggle details void QGraphicsEffect

      drawdraw ( QPainter *painter ) ( QPainter *painter ) [pure virtual protected]

      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.

      For example:

      1. MyGraphicsEffect::draw(QPainter *painter)
      2.  {
      3.     ...
      4.     QPoint offset;
      5.     if (sourceIsPixmap())  {
      6.         // No point in drawing in device coordinates (pixmap will be scaled anyways).
      7.         const QPixmap pixmap = sourcePixmap(Qt::LogicalCoordinates, &offset);
      8.         ...
      9.         painter->drawPixmap(offset, pixmap);
      10.     } else  {
      11.         // Draw pixmap in device coordinates to avoid pixmap scaling;
      12.         const QPixmap pixmap = sourcePixmap(Qt::DeviceCoordinates, &offset);
      13.         painter->setWorldTransform(QTransform());
      14.         ...
      15.         painter->drawPixmap(offset, pixmap);
      16.     }
      17.     ...
      18. }

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

      Look up this member in the source code.

      Toggle details void QGraphicsEffect

      drawSourcedrawSource ( QPainter *painter ) ( QPainter *painter )[protected]

      Draws the source directly using the given painter.

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

      For example:

      1. MyGraphicsOpacityEffect::draw(QPainter *painter)
      2.  {
      3.     // Fully opaque; draw directly without going through a pixmap.
      4.     if (qFuzzyCompare(m_opacity, 1))  {
      5.         drawSource(painter);
      6.         return;
      7.     }
      8.     ...
      9. }

      See also QGraphicsEffect::draw().

      Look up this member in the source code.

      Toggle details QRectF QGraphicsEffect

      sourceBoundingRectsourceBoundingRect ( Qt::CoordinateSystem system=Qt::LogicalCoordinates ...) ( Qt::CoordinateSystem system=Qt::LogicalCoordinates )const[protected]

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

      Calling this function with Qt::DeviceCoordinates outside of QGraphicsEffect::draw() will give undefined results, as there is no device context available.

      See also draw().

      Look up this member in the source code.

      Toggle details void QGraphicsEffect

      sourceChangedsourceChanged ( ChangeFlags flags ) ( ChangeFlags flags ) [virtual protected]

      This virtual function is called by 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.

      Look up this member in the source code.

      Toggle details bool QGraphicsEffect

      sourceIsPixmapsourceIsPixmap () ()const[protected]

      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.

      Look up this member in the source code.

      Toggle details QPixmap QGraphicsEffect

      sourcePixmapsourcePixmap ( Qt::CoordinateSystem system=Qt::LogicalCoordinates , QPoint *offset=0 , PixmapPadMode mode=PadToEffectiveBoundingRect ...) ( Qt::CoordinateSystem system=Qt::LogicalCoordinates , QPoint *offset=0 , PixmapPadMode mode=PadToEffectiveBoundingRect )const[protected]

      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 parameter.

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

      Calling this function with Qt::DeviceCoordinates outside of QGraphicsEffect::draw() will give undefined results, as there is no device context available.

      See also draw() and boundingRect().

      Look up this member in the source code.

      Toggle details void QGraphicsEffect

      updateBoundingRectupdateBoundingRect () ()[protected]

      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.

      See also boundingRectFor(), boundingRect(), and sourceBoundingRect().

      Look up this member in the source code.

        Signals

        Toggle details void QGraphicsEffect

        enabledChangedenabledChanged ( bool enabled ) ( bool enabled ) [signal]

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

        See also isEnabled().

        Look up this member in the source code.

          Public Slots

          Toggle details void QGraphicsEffect

          updateupdate () () [slot]

          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.

          See also updateBoundingRect().

          Look up this member in the source code.

            Notes provided by the Qt Community

            No notes