QCanvasView

NAME

SYNOPSIS

Inherits QScrollView.

Public Members

Protected Members

DESCRIPTION

A QCanvasView is widget which provides a view of a QCanvas.

If you want users to be able to interact with a canvas view, subclass QCanvasView. You might then reimplement QScrollView::contentsMousePressEvent(). For example, assuming no transformation matrix is set:

    void MyCanvasView::contentsMousePressEvent( QMouseEvent* e )


    {


        QCanvasItemList l = canvas()->collisions(e->pos());


        for (QCanvasItemList::Iterator it=l.begin(); it!=l.end(); ++it) {


            if ( (*it)->rtti() == QCanvasRectangle::RTTI )


                qDebug("A QCanvasRectangle lies somewhere at this point");


        }


    }

The canvas view shows canvas canvas(); this can be changed using setCanvas().

A transformation matrix can be used to transform the view of the canvas in various ways, for example, zooming in or out or rotating. For example:

    QWMatrix wm;


    wm.scale( 2, 2 );   // Zooms in by 2 times


    wm.rotate( 90 );    // Rotates 90 degrees counter clockwise


                        // around the origin.


    wm.translate( 0, -canvas->height() );


                        // moves the canvas down so what was visible


                        // before is still visible.


    myCanvasView->setWorldMatrix( wm );

Use setWorldMatrix() to set the canvas view's world matrix: you must ensure that the world matrix is invertible. The current world matrix is retrievable with worldMatrix(), and its inversion is retrievable with inverseWorldMatrix().

Example:

The following code finds the part of the canvas that is visible in this view, i.e. the bounding rectangle of the view in canvas coordinates.

    QRect rc = QRect( myCanvasView->contentsX(), myCanvasView->contentsY(),


                        myCanvasView->visibleWidth(), myCanvasView->visibleHeight() );


    QRect canvasRect = myCanvasView->inverseWorldMatrix().mapRect(rc);

See also QWMatrix, QPainter::setWorldMatrix(), Graphics Classes, and Image Processing Classes.

MEMBER FUNCTION DOCUMENTATION

QCanvasView::QCanvasView ( QWidget * parent = 0, const char * name = 0, WFlags f = 0 )

QCanvasView::QCanvasView ( QCanvas * canvas, QWidget * parent = 0, const char * name = 0, WFlags f = 0 )

Constructs a QCanvasView which views canvas canvas, with parent parent, and name name, using the widget flags f.  

QCanvasView::~QCanvasView ()

QCanvas * QCanvasView::canvas () const

void QCanvasView::drawContents ( QPainter * p, int cx, int cy, int cw, int ch ) [virtual protected]

Warning: When double buffering is enabled, drawContents() will not respect the current settings of the painter when setting up the painter for the double buffer (e.g., viewport() and window()). Also, be aware that QCanvas::update() bypasses drawContents(), which means any reimplementation of drawContents() is not called.

See also QCanvas::setDoubleBuffering().

Reimplemented from QScrollView.  

const QWMatrix & QCanvasView::inverseWorldMatrix () const

See also setWorldMatrix() and worldMatrix().  

void QCanvasView::setCanvas ( QCanvas * canvas )

bool QCanvasView::setWorldMatrix ( const QWMatrix & wm )

When you use this, you should note that the performance of the QCanvasView will decrease considerably.

Returns FALSE if wm is not invertable; otherwise returns TRUE.

See also worldMatrix(), inverseWorldMatrix(), and QWMatrix::isInvertible().

Example: canvas/canvas.cpp.  

QSize QCanvasView::sizeHint () const [virtual protected]

const QWMatrix & QCanvasView::worldMatrix () const

See also setWorldMatrix() and inverseWorldMatrix().

Example: canvas/canvas.cpp.

SEE ALSO

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