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# Q3CanvasView Class Reference

The Q3CanvasView class provides an on-screen view of a Q3Canvas. More...

    #include <Q3CanvasView>

This class is part of the Qt 3 support library. It is provided to keep old source code working. We strongly advise against using it in new code. See the Porting Guide for more information.

Part of the Qt3Support module.

Inherits Q3ScrollView.

- List of all members, including inherited members

### Public Functions

- Q3CanvasView ( QWidget * parent = 0, const char * name = 0, Qt::WFlags f = 0 )
- Q3CanvasView ( Q3Canvas * canvas, QWidget * parent = 0, const char * name = 0, Qt::WFlags f = 0 )
- ~Q3CanvasView ()
- Q3Canvas * canvas () const
- const QMatrix & inverseWorldMatrix () const
- void setCanvas ( Q3Canvas * canvas )
- bool setWorldMatrix ( const QMatrix & wm )
- const QMatrix & worldMatrix () const

- 46 public functions inherited from Q3ScrollView
- 4 public functions inherited from Q3Frame
- 13 public functions inherited from QFrame
- 183 public functions inherited from QWidget
- 28 public functions inherited from QObject
- 10 public functions inherited from QPaintDevice

### Protected Functions

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

- 17 protected functions inherited from Q3ScrollView
- 5 protected functions inherited from Q3Frame
- 39 protected functions inherited from QWidget
- 7 protected functions inherited from QObject

### Additional Inherited Members

- 10 properties inherited from Q3ScrollView
- 2 properties inherited from Q3Frame
- 6 properties inherited from QFrame
- 52 properties inherited from QWidget
- 1 property inherited from QObject
- 8 public slots inherited from Q3ScrollView
- 17 public slots inherited from QWidget
- 1 public slot inherited from QObject
- 5 signals inherited from Q3ScrollView
- 1 signal inherited from QWidget
- 1 signal inherited from QObject
- 2 static public members inherited from QFrame
- 4 static public members inherited from QWidget
- 4 static public members inherited from QObject

## Detailed Description

The Q3CanvasView class provides an on-screen view of a Q3Canvas.

A Q3CanvasView is widget which provides a view of a Q3Canvas.

If you want users to be able to interact with a canvas view, subclass Q3CanvasView. You might then reimplement Q3ScrollView::contentsMousePressEvent(). For example:

        void MyCanvasView::contentsMousePressEvent(QMouseEvent* e)
        {
            Q3CanvasItemList l = canvas()->collisions(e->pos());
            for (Q3CanvasItemList::Iterator it=l.begin(); it!=l.end(); ++it) {
                if ((*it)->rtti() == Q3CanvasRectangle::RTTI)
                    qDebug("A Q3CanvasRectangle 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:

        QMatrix 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 QMatrix and QPainter::setWorldMatrix().

## Member Function Documentation

### Q3CanvasView::Q3CanvasView ( QWidget * parent = 0, const char * name = 0, Qt::WFlags f = 0 )

Constructs a Q3CanvasView 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.

### Q3CanvasView::Q3CanvasView ( Q3Canvas * canvas, QWidget * parent = 0, const char * name = 0, Qt::WFlags f = 0 )

Constructs a Q3CanvasView which views canvas canvas, with parent parent, and name name, using the widget flags f.

### Q3CanvasView::~Q3CanvasView ()

Destroys the canvas view. The associated canvas is not deleted.

### Q3Canvas * Q3CanvasView::canvas () const

Returns a pointer to the canvas which the Q3CanvasView is currently showing.

### void Q3CanvasView::drawContents ( QPainter * p, int cx, int cy, int cw, int ch ) `[virtual protected]`

Repaints part of the Q3Canvas 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 Q3ScrollView.

### const QMatrix & Q3CanvasView::inverseWorldMatrix () const

Returns a reference to the inverse of the canvas view's current transformation matrix.

See also setWorldMatrix() and worldMatrix().

### void Q3CanvasView::setCanvas ( Q3Canvas * canvas )

Sets the canvas that the Q3CanvasView is showing to the canvas canvas.

### bool Q3CanvasView::setWorldMatrix ( const QMatrix & wm )

Sets the transformation matrix of the Q3CanvasView 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 Q3CanvasView will decrease considerably.

Returns false if wm is not invertable; otherwise returns true.

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

### QSize Q3CanvasView::sizeHint () const `[virtual protected]`

Suggests a size sufficient to view the entire canvas.

Reimplemented from QWidget.

### const QMatrix & Q3CanvasView::worldMatrix () const

Returns a reference to the canvas view's current transformation matrix.

See also setWorldMatrix() and inverseWorldMatrix().