Q3CanvasView Class Reference
[Qt3Support module]

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.

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