QCanvasView(3qt)

NAME
QCanvasView - On-screen view of a QCanvas

SYNOPSIS
#include <qcanvas.h>

Inherits QScrollView.

  Public Members
QCanvasView ( QWidget * parent = 0, const char * name = 0, WFlags f = 0 )
QCanvasView ( QCanvas * canvas, QWidget * parent = 0, const char * name = 0, WFlags f = 0 )
~QCanvasView ()
QCanvas * canvas () const
void setCanvas ( QCanvas * canvas )
const QWMatrix & worldMatrix () const
const QWMatrix & inverseWorldMatrix () const
bool setWorldMatrix ( const QWMatrix & wm )

  Protected Members
virtual void drawContents ( QPainter * p, int cx, int cy, int cw, int ch )
virtual QSize sizeHint () const

DESCRIPTION
The QCanvasView class provides an on-screen view of a QCanvas.

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:

    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 )
Constructs a QCanvasView with parent parent, and name name, using the widget flags f. The canvas view is not associated with a canvas, so you must to call setCanvas() to view a canvas.

QCanvasView::QCanvasView ( QCanvas * canvas, QWidget * parent = 0, const char * name = 0, WFlags f = 0 )
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

QCanvasView::~QCanvasView ()
Destroys the canvas view. The associated canvas is not deleted.

QCanvas * QCanvasView::canvas () const
Returns a pointer to the canvas which the QCanvasView is currently showing.

void QCanvasView::drawContents ( QPainter * p, int cx, int cy, int cw, int ch ) [virtual protected]
Repaints part of the QCanvas that the canvas view is showing starting at cx by cy, with a width of cw and a height of ch using the painter p.

Reimplemented from QScrollView.

const QWMatrix & QCanvasView::inverseWorldMatrix () const
Returns a reference to the inverse of the canvas view's current transformation matrix.

See also setWorldMatrix() and worldMatrix().

void QCanvasView::setCanvas ( QCanvas * canvas )
Sets the canvas that the QCanvasView is showing to the canvas canvas.

bool QCanvasView::setWorldMatrix ( const QWMatrix & wm )
Sets the transformation matrix of the QCanvasView to wm. The matrix must be invertible (i.e. if you create a world matrix that zooms out by 2 times, then the inverse of this matrix is one that will zoom in by 2 times).

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]
Suggests a size sufficient to view the entire canvas.

const QWMatrix & QCanvasView::worldMatrix () const
Returns a reference to the canvas view's current transformation matrix.

See also setWorldMatrix() and inverseWorldMatrix().

Example: canvas/canvas.cpp.

SEE ALSO
http://doc.trolltech.com/qcanvasview.html http://www.trolltech.com/faq/tech.html

COPYRIGHT
Copyright 1992-2001 Trolltech AS, http://www.trolltech.com. See the license file included in the distribution for a complete license statement.

AUTHOR
Generated automatically from the source code.

BUGS
If you find a bug in Qt, please report it as described in http://doc.trolltech.com/bughowto.html. Good bug reports help us to help you. Thank you.

The definitive Qt documentation is provided in HTML format; it is located at $QTDIR/doc/html and can be read using Qt Assistant or with a web browser. This man page is provided as a convenience for those users who prefer man pages, although this format is not officially supported by Trolltech.

If you find errors in this manual page, please report them to qt-bugs@trolltech.com. Please include the name of the manual page (qcanvasview.3qt) and the Qt version (3.2.1).