QGraphicsView Class

QGraphicsScene scene;
scene.addText("Hello, world!");

QGraphicsView view(&scene);
view.show();

QGraphicsView view;
view.setBackgroundBrush(QImage(":/images/backgroundtile.png"));
view.setCacheMode(QGraphicsView::CacheBackground);

QGraphicsScene scene;
scene.addRect(QRectF(-10, -10, 20, 20));

QGraphicsView view(&scene);
view.setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
view.show();

Member Function Documentation

QGraphicsView::QGraphicsView(QWidget *parent = nullptr)

Constructs a QGraphicsView. parent is passed to QWidget's constructor.

QGraphicsView::QGraphicsView(QGraphicsScene *scene, QWidget *parent = nullptr)

Constructs a QGraphicsView and sets the visualized scene to scene. parent is passed to QWidget's constructor.

[virtual] QGraphicsView::~QGraphicsView()

Destructs the QGraphicsView object.

void QGraphicsView::centerOn(const QPointF &pos)

Scrolls the contents of the viewport to ensure that the scene coordinate pos, is centered in the view.

Because pos is a floating point coordinate, and the scroll bars operate on integer coordinates, the centering is only an approximation.

Note: If the item is close to or outside the border, it will be visible in the view, but not centered.

See also ensureVisible().

void QGraphicsView::centerOn(qreal x, qreal y)

This is an overloaded function.

This function is provided for convenience. It's equivalent to calling centerOn(QPointF(x, y)).

void QGraphicsView::centerOn(const QGraphicsItem *item)

This is an overloaded function.

Scrolls the contents of the viewport to ensure that item is centered in the view.

See also ensureVisible().

[override virtual protected] void QGraphicsView::contextMenuEvent(QContextMenuEvent *event)

Reimplemented from QAbstractScrollArea::contextMenuEvent().

[override virtual protected] void QGraphicsView::dragEnterEvent(QDragEnterEvent *event)

Reimplemented from QAbstractScrollArea::dragEnterEvent().

[override virtual protected] void QGraphicsView::dragLeaveEvent(QDragLeaveEvent *event)

Reimplemented from QAbstractScrollArea::dragLeaveEvent().

[override virtual protected] void QGraphicsView::dragMoveEvent(QDragMoveEvent *event)

Reimplemented from QAbstractScrollArea::dragMoveEvent().

[virtual protected] void QGraphicsView::drawBackground(QPainter *painter, const QRectF &rect)

Draws the background of the scene using painter, before any items and the foreground are drawn. Reimplement this function to provide a custom background for this view.

If all you want is to define a color, texture or gradient for the background, you can call setBackgroundBrush() instead.

All painting is done in scene coordinates. rect is the exposed rectangle.

The default implementation fills rect using the view's backgroundBrush. If no such brush is defined (the default), the scene's drawBackground() function is called instead.

See also drawForeground() and QGraphicsScene::drawBackground().

[virtual protected] void QGraphicsView::drawForeground(QPainter *painter, const QRectF &rect)

Draws the foreground of the scene using painter, after the background and all items are drawn. Reimplement this function to provide a custom foreground for this view.

If all you want is to define a color, texture or gradient for the foreground, you can call setForegroundBrush() instead.

All painting is done in scene coordinates. rect is the exposed rectangle.

The default implementation fills rect using the view's foregroundBrush. If no such brush is defined (the default), the scene's drawForeground() function is called instead.

See also drawBackground() and QGraphicsScene::drawForeground().

[override virtual protected] void QGraphicsView::dropEvent(QDropEvent *event)

Reimplemented from QAbstractScrollArea::dropEvent().

void QGraphicsView::ensureVisible(const QRectF &rect, int xmargin = 50, int ymargin = 50)

Scrolls the contents of the viewport so that the scene rectangle rect is visible, with margins specified in pixels by xmargin and ymargin. If the specified rect cannot be reached, the contents are scrolled to the nearest valid position. The default value for both margins is 50 pixels.

See also centerOn().

void QGraphicsView::ensureVisible(qreal x, qreal y, qreal w, qreal h, int xmargin = 50, int ymargin = 50)

This is an overloaded function.

This function is provided for convenience. It's equivalent to calling ensureVisible(QRectF(x, y, w, h), xmargin, ymargin).

void QGraphicsView::ensureVisible(const QGraphicsItem *item, int xmargin = 50, int ymargin = 50)

This is an overloaded function.

Scrolls the contents of the viewport so that the center of item item is visible, with margins specified in pixels by xmargin and ymargin. If the specified point cannot be reached, the contents are scrolled to the nearest valid position. The default value for both margins is 50 pixels.

See also centerOn().

[override virtual protected] bool QGraphicsView::event(QEvent *event)

Reimplemented from QAbstractScrollArea::event().

void QGraphicsView::fitInView(const QRectF &rect, Qt::AspectRatioMode aspectRatioMode = Qt::IgnoreAspectRatio)

Scales the view matrix and scrolls the scroll bars to ensure that the scene rectangle rect fits inside the viewport. rect must be inside the scene rect; otherwise, fitInView() cannot guarantee that the whole rect is visible.

This function keeps the view's rotation, translation, or shear. The view is scaled according to aspectRatioMode. rect will be centered in the view if it does not fit tightly.

It's common to call fitInView() from inside a reimplementation of resizeEvent(), to ensure that the whole scene, or parts of the scene, scales automatically to fit the new size of the viewport as the view is resized. Note though, that calling fitInView() from inside resizeEvent() can lead to unwanted resize recursion, if the new transformation toggles the automatic state of the scrollbars. You can toggle the scrollbar policies to always on or always off to prevent this (see horizontalScrollBarPolicy() and verticalScrollBarPolicy()).

If rect is empty, or if the viewport is too small, this function will do nothing.

See also setTransform(), ensureVisible(), and centerOn().

void QGraphicsView::fitInView(qreal x, qreal y, qreal w, qreal h, Qt::AspectRatioMode aspectRatioMode = ...)

This is an overloaded function.

This convenience function is equivalent to calling fitInView(QRectF(x, y, w, h), aspectRatioMode).

See also ensureVisible() and centerOn().

void QGraphicsView::fitInView(const QGraphicsItem *item, Qt::AspectRatioMode aspectRatioMode = Qt::IgnoreAspectRatio)

This is an overloaded function.

Ensures that item fits tightly inside the view, scaling the view according to aspectRatioMode.

See also ensureVisible() and centerOn().

[override virtual protected] void QGraphicsView::focusInEvent(QFocusEvent *event)

Reimplemented from QWidget::focusInEvent().

[override virtual protected] bool QGraphicsView::focusNextPrevChild(bool next)

Reimplemented from QWidget::focusNextPrevChild().

[override virtual protected] void QGraphicsView::focusOutEvent(QFocusEvent *event)

Reimplemented from QWidget::focusOutEvent().

[override virtual protected] void QGraphicsView::inputMethodEvent(QInputMethodEvent *event)

Reimplemented from QWidget::inputMethodEvent().

[override virtual] QVariant QGraphicsView::inputMethodQuery(Qt::InputMethodQuery query) const

Reimplemented from QWidget::inputMethodQuery().

[slot] void QGraphicsView::invalidateScene(const QRectF &rect, QGraphicsScene::SceneLayers layers)

Invalidates and schedules a redraw of layers inside rect. rect is in scene coordinates. Any cached content for layers inside rect is unconditionally invalidated and redrawn.

You can call this function to notify QGraphicsView of changes to the background or the foreground of the scene. It is commonly used for scenes with tile-based backgrounds to notify changes when QGraphicsView has enabled background caching.

Note that QGraphicsView currently supports background caching only (see QGraphicsView::CacheBackground). This function is equivalent to calling update() if any layer but QGraphicsScene::BackgroundLayer is passed.

See also QGraphicsScene::invalidate() and update().

bool QGraphicsView::isTransformed() const

Returns true if the view is transformed (i.e., a non-identity transform has been assigned, or the scrollbars are adjusted).

This function was introduced in Qt 4.6.

See also setTransform(), horizontalScrollBar(), and verticalScrollBar().

QGraphicsItem *QGraphicsView::itemAt(const QPoint &pos) const

Returns the item at position pos, which is in viewport coordinates. If there are several items at this position, this function returns the topmost item.

Example:

void CustomView::mousePressEvent(QMouseEvent *event)
{
    if (QGraphicsItem *item = itemAt(event->pos())) {
        qDebug() << "You clicked on item" << item;
    } else {
        qDebug("You didn't click on an item.");
    }
}

See also items() and Sorting.

QGraphicsItem *QGraphicsView::itemAt(int x, int y) const

This is an overloaded function.

This function is provided for convenience. It's equivalent to calling itemAt(QPoint(x, y)).

QList<QGraphicsItem *> QGraphicsView::items() const

Returns a list of all the items in the associated scene, in descending stacking order (i.e., the first item in the returned list is the uppermost item).

See also QGraphicsScene::items() and Sorting.

QList<QGraphicsItem *> QGraphicsView::items(const QPoint &pos) const

Returns a list of all the items at the position pos in the view. The items are listed in descending stacking order (i.e., the first item in the list is the uppermost item, and the last item is the lowermost item). pos is in viewport coordinates.

This function is most commonly called from within mouse event handlers in a subclass in QGraphicsView. pos is in untransformed viewport coordinates, just like QMouseEvent::pos().

void CustomView::mousePressEvent(QMouseEvent *event)
{
    qDebug() << "There are" << items(event->pos()).size()
             << "items at position" << mapToScene(event->pos());
}

See also QGraphicsScene::items() and Sorting.

QList<QGraphicsItem *> QGraphicsView::items(int x, int y) const

This function is provided for convenience. It's equivalent to calling items(QPoint(x, y)).

QList<QGraphicsItem *> QGraphicsView::items(const QRect &rect, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const

This is an overloaded function.

Returns a list of all the items that, depending on mode, are either contained by or intersect with rect. rect is in viewport coordinates.

The default value for mode is Qt::IntersectsItemShape; all items whose exact shape intersects with or is contained by rect are returned.

The items are sorted in descending stacking order (i.e., the first item in the returned list is the uppermost item).

See also itemAt(), items(), mapToScene(), and Sorting.

QList<QGraphicsItem *> QGraphicsView::items(int x, int y, int w, int h, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const

This convenience function is equivalent to calling items(QRectF(x, y, w, h), mode).

This function was introduced in Qt 4.3.

QList<QGraphicsItem *> QGraphicsView::items(const QPolygon &polygon, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const

This is an overloaded function.

Returns a list of all the items that, depending on mode, are either contained by or intersect with polygon. polygon is in viewport coordinates.

The default value for mode is Qt::IntersectsItemShape; all items whose exact shape intersects with or is contained by polygon are returned.

The items are sorted by descending stacking order (i.e., the first item in the returned list is the uppermost item).

See also itemAt(), items(), mapToScene(), and Sorting.

QList<QGraphicsItem *> QGraphicsView::items(const QPainterPath &path, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const

This is an overloaded function.

Returns a list of all the items that, depending on mode, are either contained by or intersect with path. path is in viewport coordinates.

The default value for mode is Qt::IntersectsItemShape; all items whose exact shape intersects with or is contained by path are returned.

See also itemAt(), items(), mapToScene(), and Sorting.

[override virtual protected] void QGraphicsView::keyPressEvent(QKeyEvent *event)

Reimplemented from QAbstractScrollArea::keyPressEvent().

[override virtual protected] void QGraphicsView::keyReleaseEvent(QKeyEvent *event)

Reimplemented from QWidget::keyReleaseEvent().

QPoint QGraphicsView::mapFromScene(const QPointF &point) const

Returns the scene coordinate point to viewport coordinates.

See also mapToScene().

QPolygon QGraphicsView::mapFromScene(const QRectF &rect) const

Returns the scene rectangle rect to a viewport coordinate polygon.

See also mapToScene().

QPolygon QGraphicsView::mapFromScene(const QPolygonF &polygon) const

Returns the scene coordinate polygon polygon to a viewport coordinate polygon.

See also mapToScene().

QPainterPath QGraphicsView::mapFromScene(const QPainterPath &path) const

Returns the scene coordinate painter path path to a viewport coordinate painter path.

See also mapToScene().

QPoint QGraphicsView::mapFromScene(qreal x, qreal y) const

This function is provided for convenience. It's equivalent to calling mapFromScene(QPointF(x, y)).

QPolygon QGraphicsView::mapFromScene(qreal x, qreal y, qreal w, qreal h) const

This function is provided for convenience. It's equivalent to calling mapFromScene(QRectF(x, y, w, h)).

QPointF QGraphicsView::mapToScene(const QPoint &point) const

Returns the viewport coordinate point mapped to scene coordinates.

Note: It can be useful to map the whole rectangle covered by the pixel at point instead of the point itself. To do this, you can call mapToScene(QRect(point, QSize(2, 2))).

See also mapFromScene().

QPolygonF QGraphicsView::mapToScene(const QRect &rect) const

Returns the viewport rectangle rect mapped to a scene coordinate polygon.

See also mapFromScene().

QPolygonF QGraphicsView::mapToScene(const QPolygon &polygon) const

Returns the viewport polygon polygon mapped to a scene coordinate polygon.

See also mapFromScene().

QPainterPath QGraphicsView::mapToScene(const QPainterPath &path) const

Returns the viewport painter path path mapped to a scene coordinate painter path.

See also mapFromScene().

QPointF QGraphicsView::mapToScene(int x, int y) const

This function is provided for convenience. It's equivalent to calling mapToScene(QPoint(x, y)).

QPolygonF QGraphicsView::mapToScene(int x, int y, int w, int h) const

This function is provided for convenience. It's equivalent to calling mapToScene(QRect(x, y, w, h)).

QMatrix QGraphicsView::matrix() const

Returns the current transformation matrix for the view. If no current transformation is set, the identity matrix is returned.

See also setMatrix(), transform(), rotate(), scale(), shear(), and translate().

[override virtual protected] void QGraphicsView::mouseDoubleClickEvent(QMouseEvent *event)

Reimplemented from QAbstractScrollArea::mouseDoubleClickEvent().

[override virtual protected] void QGraphicsView::mouseMoveEvent(QMouseEvent *event)

Reimplemented from QAbstractScrollArea::mouseMoveEvent().

[override virtual protected] void QGraphicsView::mousePressEvent(QMouseEvent *event)

Reimplemented from QAbstractScrollArea::mousePressEvent().

[override virtual protected] void QGraphicsView::mouseReleaseEvent(QMouseEvent *event)

Reimplemented from QAbstractScrollArea::mouseReleaseEvent().

[override virtual protected] void QGraphicsView::paintEvent(QPaintEvent *event)

Reimplemented from QAbstractScrollArea::paintEvent().

void QGraphicsView::render(QPainter *painter, const QRectF &target = QRectF(), const QRect &source = QRect(), Qt::AspectRatioMode aspectRatioMode = Qt::KeepAspectRatio)

Renders the source rect, which is in view coordinates, from the scene into target, which is in paint device coordinates, using painter. This function is useful for capturing the contents of the view onto a paint device, such as a QImage (e.g., to take a screenshot), or for printing to QPrinter. For example:

QGraphicsScene scene;
scene.addItem(...
...

QGraphicsView view(&scene);
view.show();
...

QPrinter printer(QPrinter::HighResolution);
printer.setPageSize(QPrinter::A4);
QPainter painter(&printer);

// print, fitting the viewport contents into a full page
view.render(&painter);

// print the upper half of the viewport into the lower.
// half of the page.
QRect viewport = view.viewport()->rect();
view.render(&painter,
            QRectF(0, printer.height() / 2,
                   printer.width(), printer.height() / 2),
            viewport.adjusted(0, 0, 0, -viewport.height() / 2));

If source is a null rect, this function will use viewport()->rect() to determine what to draw. If target is a null rect, the full dimensions of painter's paint device (e.g., for a QPrinter, the page size) will be used.

The source rect contents will be transformed according to aspectRatioMode to fit into the target rect. By default, the aspect ratio is kept, and source is scaled to fit in target.

See also QGraphicsScene::render().

void QGraphicsView::resetCachedContent()

Resets any cached content. Calling this function will clear QGraphicsView's cache. If the current cache mode is CacheNone, this function does nothing.

This function is called automatically for you when the backgroundBrush or QGraphicsScene::backgroundBrush properties change; you only need to call this function if you have reimplemented QGraphicsScene::drawBackground() or QGraphicsView::drawBackground() to draw a custom background, and need to trigger a full redraw.

See also cacheMode().

void QGraphicsView::resetMatrix()

Resets the view transformation matrix to the identity matrix.

See also resetTransform().

void QGraphicsView::resetTransform()

Resets the view transformation to the identity matrix.

See also transform() and setTransform().

[override virtual protected] void QGraphicsView::resizeEvent(QResizeEvent *event)

Reimplemented from QAbstractScrollArea::resizeEvent().

void QGraphicsView::rotate(qreal angle)

Rotates the current view transformation angle degrees clockwise.

See also setTransform(), transform(), scale(), shear(), and translate().

[signal] void QGraphicsView::rubberBandChanged(QRect rubberBandRect, QPointF fromScenePoint, QPointF toScenePoint)

This signal is emitted when the rubber band rect is changed. The viewport Rect is specified by rubberBandRect. The drag start position and drag end position are provided in scene points with fromScenePoint and toScenePoint.

When rubberband selection ends this signal will be emitted with null vales.

This function was introduced in Qt 5.1.

See also rubberBandRect().

QRect QGraphicsView::rubberBandRect() const

This functions returns the current rubber band area (in viewport coordinates) if the user is currently doing an itemselection with rubber band. When the user is not using the rubber band this functions returns (a null) QRectF().

Notice that part of this QRect can be outise the visual viewport. It can e.g contain negative values.

This function was introduced in Qt 5.1.

See also rubberBandSelectionMode and rubberBandChanged().

void QGraphicsView::scale(qreal sx, qreal sy)

Scales the current view transformation by (sx, sy).

See also setTransform(), transform(), rotate(), shear(), and translate().

QGraphicsScene *QGraphicsView::scene() const

Returns a pointer to the scene that is currently visualized in the view. If no scene is currently visualized, 0 is returned.

See also setScene().

[override virtual protected] void QGraphicsView::scrollContentsBy(int dx, int dy)

Reimplemented from QAbstractScrollArea::scrollContentsBy().

void QGraphicsView::setMatrix(const QMatrix &matrix, bool combine = false)

Sets the view's current transformation matrix to matrix.

If combine is true, then matrix is combined with the current matrix; otherwise, matrix replaces the current matrix. combine is false by default.

The transformation matrix tranforms the scene into view coordinates. Using the default transformation, provided by the identity matrix, one pixel in the view represents one unit in the scene (e.g., a 10x10 rectangular item is drawn using 10x10 pixels in the view). If a 2x2 scaling matrix is applied, the scene will be drawn in 1:2 (e.g., a 10x10 rectangular item is then drawn using 20x20 pixels in the view).

Example:

QGraphicsScene scene;
scene.addText("GraphicsView rotated clockwise");

QGraphicsView view(&scene);
view.rotate(90); // the text is rendered with a 90 degree clockwise rotation
view.show();

To simplify interation with items using a transformed view, QGraphicsView provides mapTo... and mapFrom... functions that can translate between scene and view coordinates. For example, you can call mapToScene() to map a view coordinate to a floating point scene coordinate, or mapFromScene() to map from floating point scene coordinates to view coordinates.

See also matrix(), setTransform(), rotate(), scale(), shear(), and translate().

void QGraphicsView::setOptimizationFlag(QGraphicsView::OptimizationFlag flag, bool enabled = true)

Enables flag if enabled is true; otherwise disables flag.

See also optimizationFlags.

void QGraphicsView::setRenderHint(QPainter::RenderHint hint, bool enabled = true)

If enabled is true, the render hint hint is enabled; otherwise it is disabled.

See also renderHints.

void QGraphicsView::setScene(QGraphicsScene *scene)

Sets the current scene to scene. If scene is already being viewed, this function does nothing.

When a scene is set on a view, the QGraphicsScene::changed() signal is automatically connected to this view's updateScene() slot, and the view's scroll bars are adjusted to fit the size of the scene.

The view does not take ownership of scene.

See also scene().

void QGraphicsView::setTransform(const QTransform &matrix, bool combine = false)

Sets the view's current transformation matrix to matrix.

If combine is true, then matrix is combined with the current matrix; otherwise, matrix replaces the current matrix. combine is false by default.

The transformation matrix tranforms the scene into view coordinates. Using the default transformation, provided by the identity matrix, one pixel in the view represents one unit in the scene (e.g., a 10x10 rectangular item is drawn using 10x10 pixels in the view). If a 2x2 scaling matrix is applied, the scene will be drawn in 1:2 (e.g., a 10x10 rectangular item is then drawn using 20x20 pixels in the view).

Example:

QGraphicsScene scene;
scene.addText("GraphicsView rotated clockwise");

QGraphicsView view(&scene);
view.rotate(90); // the text is rendered with a 90 degree clockwise rotation
view.show();

To simplify interation with items using a transformed view, QGraphicsView provides mapTo... and mapFrom... functions that can translate between scene and view coordinates. For example, you can call mapToScene() to map a view coordiate to a floating point scene coordinate, or mapFromScene() to map from floating point scene coordinates to view coordinates.

See also transform(), rotate(), scale(), shear(), and translate().

[override virtual protected slot] void QGraphicsView::setupViewport(QWidget *widget)

Reimplemented from QAbstractScrollArea::setupViewport().

This slot is called by QAbstractScrollArea after setViewport() has been called. Reimplement this function in a subclass of QGraphicsView to initialize the new viewport widget before it is used.

See also setViewport().

void QGraphicsView::shear(qreal sh, qreal sv)

Shears the current view transformation by (sh, sv).

See also setTransform(), transform(), rotate(), scale(), and translate().

[override virtual protected] void QGraphicsView::showEvent(QShowEvent *event)

Reimplemented from QWidget::showEvent().

[override virtual] QSize QGraphicsView::sizeHint() const

Reimplemented from QAbstractScrollArea::sizeHint().

QTransform QGraphicsView::transform() const

Returns the current transformation matrix for the view. If no current transformation is set, the identity matrix is returned.

See also setTransform(), rotate(), scale(), shear(), and translate().

void QGraphicsView::translate(qreal dx, qreal dy)

Translates the current view transformation by (dx, dy).

See also setTransform(), transform(), rotate(), and shear().

[slot] void QGraphicsView::updateScene(const QList<QRectF> &rects)

Schedules an update of the scene rectangles rects.

See also QGraphicsScene::changed().

[slot] void QGraphicsView::updateSceneRect(const QRectF &rect)

Notifies QGraphicsView that the scene's scene rect has changed. rect is the new scene rect. If the view already has an explicitly set scene rect, this function does nothing.

See also sceneRect and QGraphicsScene::sceneRectChanged().

[override virtual protected] bool QGraphicsView::viewportEvent(QEvent *event)

Reimplemented from QAbstractScrollArea::viewportEvent().

QTransform QGraphicsView::viewportTransform() const

Returns a matrix that maps scene coordinates to viewport coordinates.

See also mapToScene() and mapFromScene().

[override virtual protected] void QGraphicsView::wheelEvent(QWheelEvent *event)

Reimplemented from QAbstractScrollArea::wheelEvent().