QCanvasView(3qt)

📦 version 3.3.8b, in fedora 43, fedora 44

✨ QCanvasView(3qt) ✨

okay bestie, so this is the manual page for QCanvasView from Qt 3.3.8, brought to you by Trolltech (the man page itself is dated 2 February 2007, we'll get to that at the end 🫶). It's a 3qt page, which means it's a Qt library manual. Let's get into it 💅

🌸 NAME 🌸

QCanvasView — an on-screen view of a QCanvas 👀✨

🎀 SYNOPSIS 🎀

#include <qcanvas.h>

Inherits QScrollView. Yes, she's a widget, she's got lineage 💅

✨ Public Members ✨

  • QCanvasView ( QWidget * parent = 0, const char * name = 0, WFlags f = 0 )
  • QCanvasView ( QCanvas * canvas, QWidget * parent = 0, const char * name = 0, WFlags f = 0 )
  • ~QCanvasView ()
  • QCanvas * canvas () const
  • void setCanvas ( QCanvas * canvas )
  • const QWMatrix & worldMatrix () const
  • const QWMatrix & inverseWorldMatrix () const
  • bool setWorldMatrix ( const QWMatrix & wm )

🦋 Protected Members 🦋

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

💖 DESCRIPTION 💖

The QCanvasView class provides an on-screen view of a QCanvas. That's the whole vibe, periodt.

A QCanvasView is a widget which provides a view of a QCanvas. 🎨

So like — if you want users to actually be able to interact with a canvas view, you subclass QCanvasView. Then you'd probably 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(); and bestie, you can change that with 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. Like so:

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. Heads up though: the canvas view is not associated with a canvas, so you must call setCanvas() to view a canvas. Don't forget, or she's just sitting there with nothing to show 😭

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. (Classic convenience behavior, we love her 🙈)

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 — important!! She does not take the canvas down with her, no cap 💀

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. 🚨 like, actually be aware, bestie.

See also QCanvas::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. Swapsies ✨

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. 😬 lowkey a price to pay, fr fr.

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. She's suggesting, not demanding 💅

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.

🌈 SEE ALSO 🌈

Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the license file included in the distribution for a complete license statement.

🍓 AUTHOR 🍓

Generated automatically from the source code. (Not a human bestie, a script bestie 🤖✨)

💀 BUGS 💀

If you find a bug in Qt, please report it as described in http://doc.trolltech.com/bughowto.html. Good bug reports help us to help you. Thank you. 🫶

The definitive Qt documentation is provided in HTML format; it is located at $QTDIR/doc/html and can be read using Qt Assistant or with a web browser. This man page is provided as a convenience for those users who prefer man pages, although this format is not officially supported by Trolltech.

If you find errors in this manual page, please report them to qt-bugs@trolltech.com. Please include the name of the manual page (qcanvasview.3qt) and the Qt version (3.3.8).

aaaand that's the whole page bestie 🎀 this was QCanvasView(3qt) from the Qt 3.3.8 docs, published by Trolltech AS on 2 February 2007 — go forth and draw on your canvas, you've got this 💜🦋✨

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