CODEWITHSUNDEEP
c++qtqgraphicsview
mpen
mpen

Reputation: 282875

Get visible rectangle of QGraphicsView?

I've been pulling my hair out with this one for hours. There's a thread here about it, but nothing seems to be working. QGraphicsView::rect() will return the width and height, but the left and top values aren't set properly (always 0 -- ignoring the scrolled amount). I want it in scene coordinates, but it should be easy enough to translate from any system. I have no idea what horizontalScrollBar()->value() and vert are returning...seems to be meaningless jibberish.

@fabrizioM:

// created here
void EditorWindow::createScene() {
    m_scene = new EditorScene(this);
    m_view = new EditorView(m_scene);
    setCentralWidget(m_view);
    connect(m_scene, SIGNAL(mousePosChanged(QPointF)), this, SLOT(mousePosChanged(QPointF)));
}

/// with this constructor
EditorView::EditorView(QGraphicsScene* scene, QWidget* parent) : QGraphicsView(scene, parent) {
    setRenderHint(QPainter::Antialiasing);
    setCacheMode(QGraphicsView::CacheBackground);
    setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
    setDragMode(QGraphicsView::NoDrag);
    scale(1.0, -1.0); // flip coordinate system so that y increases upwards
    fitInView(-5, -5, 10, 10, Qt::KeepAspectRatio);
    setInteractive(true);
    setBackgroundBrush(QBrush(QColor(232,232,232), Qt::DiagCrossPattern));
}

Upvotes: 19

Views: 23203

Answers (7)

David Faure
David Faure

Reputation: 1997

Qt5/Qt6 version of the solution by @mpen:

QRectF EditorView::visibleRect() {
    const QRect viewportRect(QPoint(horizontalScrollBar()->value(), verticalScrollBar()->value()), viewport()->size());
    const auto mat = transform().inverted();
    return mat.mapRect(viewportRect);
}

Upvotes: 1

Bernhard
Bernhard

Reputation: 39

QRectF XXX::getCurrrentlyVisibleRegion() const
{
        //to receive the currently visible area, map the widgets bounds to the scene

        QPointF topLeft = mapToScene (0, 0);
        QPointF bottomRight = mapToScene (this->width(), this->height());

        return QRectF (topLeft, bottomRight);
}

Upvotes: 3

Ralph Tandetzky
Ralph Tandetzky

Reputation: 23610

The following implementation returned the best results for me:

QRectF getVisibleRect( QGraphicsView * view )
{
    QPointF A = view->mapToScene( QPoint(0, 0) ); 
    QPointF B = view->mapToScene( QPoint( 
        view->viewport()->width(), 
        view->viewport()->height() ));
    return QRectF( A, B );
}

This works still really well when scrollbars appear. This only works properly if the view does not display the scene rotated or sheared. If the view is rotated or sheared, then the visible rectangle is not axis parallel in the scene coordinate system. In this case

view->mapToScene( view->viewport()->geometry() )

returns a QPolygonF (NOT a QRectF) which is the visible rectangle in scene coordinates. By the way, QPolygonF has a member function boundingRect() which does not return the properly visible rectangle of the view, but might be useful anyways.

Upvotes: 5

Henrik Hartz
Henrik Hartz

Reputation: 3675

It sounds like what you want is the scene rectangle. The ::rect() method is inherited from QWidget. See:

http://doc.qt.io/qt-5/qgraphicsview.html#sceneRect-prop

Upvotes: 0

Marcel Taeumel
Marcel Taeumel

Reputation: 594

Just map the pixel-based viewport rectangle to the scene using the view:

graphicsView->mapToScene(graphicsView->viewport()->geometry()).boundingRect()

Bye, Marcel

Upvotes: 29

SixDegrees
SixDegrees

Reputation:

You can do what you've done, or use the mapToScene() functions. You can't count on the resulting scene "rectangle" being a rectangle, however, because the scene might be rotated or sheared in the view, resulting in a general polygon when mapped to the scene.

If your application never does such things, of course, you're free to assume that a rectangle is always appropriate.

Upvotes: 2

mpen
mpen

Reputation: 282875

Nevermind. Came up with this, which seems to work.

QRectF EditorView::visibleRect() {
    QPointF tl(horizontalScrollBar()->value(), verticalScrollBar()->value());
    QPointF br = tl + viewport()->rect().bottomRight();
    QMatrix mat = matrix().inverted();
    return mat.mapRect(QRectF(tl,br));
}

Upvotes: 9

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