Detailed 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.
This file is part of the Qt toolkit.
Copyright © 1995-2003
Trolltech. All Rights Reserved.
