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6<title>QCanvasView Class</title>
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32<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QCanvasView Class Reference<br><small>[<a href="canvas.html">canvas module</a>]</small></h1>
33
34<p>The QCanvasView class provides an on-screen view of a QCanvas.
35<a href="#details">More...</a>
36<p><tt>#include &lt;<a href="qcanvas-h.html">qcanvas.h</a>&gt;</tt>
37<p>Inherits <a href="qscrollview.html">QScrollView</a>.
38<p><a href="qcanvasview-members.html">List of all member functions.</a>
39<h2>Public Members</h2>
40<ul>
41<li class=fn><a href="#QCanvasView"><b>QCanvasView</b></a> ( QWidget&nbsp;*&nbsp;parent = 0, const&nbsp;char&nbsp;*&nbsp;name = 0, WFlags&nbsp;f = 0 )</li>
42<li class=fn><a href="#QCanvasView-2"><b>QCanvasView</b></a> ( QCanvas&nbsp;*&nbsp;canvas, QWidget&nbsp;*&nbsp;parent = 0, const&nbsp;char&nbsp;*&nbsp;name = 0, WFlags&nbsp;f = 0 )</li>
43<li class=fn><a href="#~QCanvasView"><b>~QCanvasView</b></a> ()</li>
44<li class=fn>QCanvas * <a href="#canvas"><b>canvas</b></a> () const</li>
45<li class=fn>void <a href="#setCanvas"><b>setCanvas</b></a> ( QCanvas&nbsp;*&nbsp;canvas )</li>
46<li class=fn>const QWMatrix &amp; <a href="#worldMatrix"><b>worldMatrix</b></a> () const</li>
47<li class=fn>const QWMatrix &amp; <a href="#inverseWorldMatrix"><b>inverseWorldMatrix</b></a> () const</li>
48<li class=fn>bool <a href="#setWorldMatrix"><b>setWorldMatrix</b></a> ( const&nbsp;QWMatrix&nbsp;&amp;&nbsp;wm )</li>
49</ul>
50<h2>Protected Members</h2>
51<ul>
52<li class=fn>virtual void <a href="#drawContents"><b>drawContents</b></a> ( QPainter&nbsp;*&nbsp;p, int&nbsp;cx, int&nbsp;cy, int&nbsp;cw, int&nbsp;ch )</li>
53<li class=fn>virtual QSize <a href="#sizeHint"><b>sizeHint</b></a> () const</li>
54</ul>
55<hr><a name="details"></a><h2>Detailed Description</h2>
56
57
58The QCanvasView class provides an on-screen view of a <a href="qcanvas.html">QCanvas</a>.
59
60<p>
61
62
63<p> A QCanvasView is widget which provides a view of a QCanvas.
64<p> If you want users to be able to interact with a canvas view,
65subclass QCanvasView. You might then reimplement
66<a href="qscrollview.html#contentsMousePressEvent">QScrollView::contentsMousePressEvent</a>(). For example, assuming no
67<a href="qwmatrix.html#TransformationMode">transformation matrix</a> is set:
68<p> <pre>
69 void MyCanvasView::contentsMousePressEvent( <a href="qmouseevent.html">QMouseEvent</a>* e )
70 {
71 <a href="qcanvasitemlist.html">QCanvasItemList</a> l = <a href="#canvas">canvas</a>()-&gt;collisions(e-&gt;<a href="qmouseevent.html#pos">pos</a>());
72 for (QCanvasItemList::Iterator it=l.<a href="qvaluelist.html#begin">begin</a>(); it!=l.<a href="qvaluelist.html#end">end</a>(); ++it) {
73 if ( (*it)-&gt;rtti() == QCanvasRectangle::RTTI )
74 <a href="qapplication.html#qDebug">qDebug</a>("A QCanvasRectangle lies somewhere at this point");
75 }
76 }
77 </pre>
78
79<p> The canvas view shows canvas <a href="#canvas">canvas</a>(); this can be changed using
80<a href="#setCanvas">setCanvas</a>().
81<p> A transformation matrix can be used to transform the view of the
82canvas in various ways, for example, zooming in or out or rotating.
83For example:
84<p> <pre>
85 <a href="qwmatrix.html">QWMatrix</a> wm;
86 wm.<a href="qwmatrix.html#scale">scale</a>( 2, 2 ); // Zooms in by 2 times
87 wm.<a href="qwmatrix.html#rotate">rotate</a>( 90 ); // Rotates 90 degrees counter clockwise
88 // around the origin.
89 wm.<a href="qwmatrix.html#translate">translate</a>( 0, -canvas-&gt;height() );
90 // moves the canvas down so what was visible
91 // before is still visible.
92 myCanvasView-&gt;setWorldMatrix( wm );
93 </pre>
94
95<p> Use <a href="#setWorldMatrix">setWorldMatrix</a>() to set the canvas view's world matrix: you must
96ensure that the world matrix is invertible. The current world matrix
97is retrievable with <a href="#worldMatrix">worldMatrix</a>(), and its inversion is retrievable
98with <a href="#inverseWorldMatrix">inverseWorldMatrix</a>().
99<p> Example:
100<p> The following code finds the part of the canvas that is visible in
101this view, i.e. the bounding rectangle of the view in canvas coordinates.
102<p> <pre>
103 <a href="qrect.html">QRect</a> rc = QRect( myCanvasView-&gt;contentsX(), myCanvasView-&gt;contentsY(),
104 myCanvasView-&gt;visibleWidth(), myCanvasView-&gt;visibleHeight() );
105 <a href="qrect.html">QRect</a> canvasRect = myCanvasView-&gt;inverseWorldMatrix().mapRect(rc);
106 </pre>
107
108<p> <p>See also <a href="qwmatrix.html">QWMatrix</a>, <a href="qpainter.html#setWorldMatrix">QPainter::setWorldMatrix</a>(), <a href="graphics.html">Graphics Classes</a>, and <a href="images.html">Image Processing Classes</a>.
109
110<p>
111<hr><h2>Member Function Documentation</h2>
112<h3 class=fn><a name="QCanvasView"></a>QCanvasView::QCanvasView ( <a href="qwidget.html">QWidget</a>&nbsp;*&nbsp;parent = 0, const&nbsp;char&nbsp;*&nbsp;name = 0, WFlags&nbsp;f = 0 )
113</h3>
114Constructs a QCanvasView with parent <em>parent</em>, and name <em>name</em>,
115using the widget flags <em>f</em>. The canvas view is not associated
116with a canvas, so you must to call <a href="#setCanvas">setCanvas</a>() to view a
117canvas.
118
119<h3 class=fn><a name="QCanvasView-2"></a>QCanvasView::QCanvasView ( <a href="qcanvas.html">QCanvas</a>&nbsp;*&nbsp;canvas, <a href="qwidget.html">QWidget</a>&nbsp;*&nbsp;parent = 0, const&nbsp;char&nbsp;*&nbsp;name = 0, WFlags&nbsp;f = 0 )
120</h3>
121This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
122<p> Constructs a QCanvasView which views canvas <em>canvas</em>, with parent
123<em>parent</em>, and name <em>name</em>, using the widget flags <em>f</em>.
124
125<h3 class=fn><a name="~QCanvasView"></a>QCanvasView::~QCanvasView ()
126</h3>
127Destroys the canvas view. The associated canvas is <em>not</em> deleted.
128
129<h3 class=fn><a href="qcanvas.html">QCanvas</a>&nbsp;* <a name="canvas"></a>QCanvasView::canvas () const
130</h3>
131
132<p> Returns a pointer to the canvas which the QCanvasView is currently
133showing.
134
135<h3 class=fn>void <a name="drawContents"></a>QCanvasView::drawContents ( <a href="qpainter.html">QPainter</a>&nbsp;*&nbsp;p, int&nbsp;cx, int&nbsp;cy, int&nbsp;cw, int&nbsp;ch )<tt> [virtual protected]</tt>
136</h3>
137Repaints part of the <a href="qcanvas.html">QCanvas</a> that the canvas view is showing
138starting at <em>cx</em> by <em>cy</em>, with a width of <em>cw</em> and a height of <em>ch</em> using the painter <em>p</em>.
139<p> <b>Warning:</b> When double buffering is enabled, <a href="#drawContents">drawContents</a>() will
140not respect the current settings of the painter when setting up
141the painter for the double buffer (e.g., <a href="qscrollview.html#viewport">viewport</a>() and
142window()). Also, be aware that <a href="qcanvas.html#update">QCanvas::update</a>() bypasses
143drawContents(), which means any reimplementation of
144drawContents() is not called.
145<p> <p>See also <a href="qcanvas.html#setDoubleBuffering">QCanvas::setDoubleBuffering</a>().
146
147<p>Reimplemented from <a href="qscrollview.html#drawContents">QScrollView</a>.
148<h3 class=fn>const&nbsp;<a href="qwmatrix.html">QWMatrix</a>&nbsp;&amp; <a name="inverseWorldMatrix"></a>QCanvasView::inverseWorldMatrix () const
149</h3>
150Returns a reference to the inverse of the canvas view's current
151<a href="qwmatrix.html#TransformationMode">transformation matrix</a>.
152<p> <p>See also <a href="#setWorldMatrix">setWorldMatrix</a>() and <a href="#worldMatrix">worldMatrix</a>().
153
154<h3 class=fn>void <a name="setCanvas"></a>QCanvasView::setCanvas ( <a href="qcanvas.html">QCanvas</a>&nbsp;*&nbsp;canvas )
155</h3>
156Sets the canvas that the QCanvasView is showing to the canvas <em>canvas</em>.
157
158<h3 class=fn>bool <a name="setWorldMatrix"></a>QCanvasView::setWorldMatrix ( const&nbsp;<a href="qwmatrix.html">QWMatrix</a>&nbsp;&amp;&nbsp;wm )
159</h3>
160Sets the <a href="qwmatrix.html#TransformationMode">transformation matrix</a> of the QCanvasView to <em>wm</em>. The
161matrix must be invertible (i.e. if you create a world matrix that
162zooms out by 2 times, then the inverse of this matrix is one that
163will zoom in by 2 times).
164<p> When you use this, you should note that the performance of the
165QCanvasView will decrease considerably.
166<p> Returns FALSE if <em>wm</em> is not invertable; otherwise returns TRUE.
167<p> <p>See also <a href="#worldMatrix">worldMatrix</a>(), <a href="#inverseWorldMatrix">inverseWorldMatrix</a>(), and <a href="qwmatrix.html#isInvertible">QWMatrix::isInvertible</a>().
168
169<p>Example: <a href="canvas-example.html#x2930">canvas/canvas.cpp</a>.
170<h3 class=fn><a href="qsize.html">QSize</a> <a name="sizeHint"></a>QCanvasView::sizeHint () const<tt> [virtual protected]</tt>
171</h3>
172Suggests a size sufficient to view the entire canvas.
173
174<h3 class=fn>const&nbsp;<a href="qwmatrix.html">QWMatrix</a>&nbsp;&amp; <a name="worldMatrix"></a>QCanvasView::worldMatrix () const
175</h3>
176Returns a reference to the canvas view's current <a href="qwmatrix.html#TransformationMode">transformation matrix</a>.
177<p> <p>See also <a href="#setWorldMatrix">setWorldMatrix</a>() and <a href="#inverseWorldMatrix">inverseWorldMatrix</a>().
178
179<p>Example: <a href="canvas-example.html#x2931">canvas/canvas.cpp</a>.
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