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, assuming no
transformation matrix is set:
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.
Warning: When double buffering is enabled, drawContents() will
not respect the current settings of the painter when setting up
the painter for the double buffer (e.g., viewport() and
window()). Also, be aware that QCanvas::update() bypasses
drawContents(), which means any reimplementation of
drawContents() is not called.
See also setDoubleBuffering().
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.
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