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# Q3CanvasView Class Reference
[Qt3Support module]

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 Porting to Qt 4 for more information.

Note to Qt Desktop Light Edition users: This class is only available in the Qt Desktop Edition.

Inherits Q3ScrollView.

- List of all members, including inherited members

### Public Functions

- Q3CanvasView ( QWidget * parent = 0, const char * name = 0, Qt::WindowFlags f = 0 )
- Q3CanvasView ( Q3Canvas * canvas, QWidget * parent = 0, const char * name = 0, Qt::WindowFlags 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
- 206 public functions inherited from QWidget
- 29 public functions inherited from QObject
- 14 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
- 38 protected functions inherited from QWidget
- 7 protected functions inherited from QObject
- 1 protected function inherited from QPaintDevice

### Additional Inherited Members

- 10 properties inherited from Q3ScrollView
- 2 properties inherited from Q3Frame
- 6 properties inherited from QFrame
- 57 properties inherited from QWidget
- 1 property inherited from QObject
- 8 public slots inherited from Q3ScrollView
- 19 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
- 4 static public members inherited from QWidget
- 5 static public members inherited from QObject
- 1 static public member inherited from QPaintDevice
- 1 protected slot inherited from QWidget

## 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, QPainter::setWorldMatrix(), QtCanvas, and Porting to Graphics View.

## Member Function Documentation

### Q3CanvasView::Q3CanvasView ( QWidget * parent = 0, const char * name = 0, Qt::WindowFlags 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::WindowFlags 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.

See also setCanvas().

### 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.

See also 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().