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123 lines
5.5 KiB
123 lines
5.5 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/misc.doc:1031 -->
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>Window Geometry</title>
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<tr bgcolor="#E5E5E5">
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<td valign=center>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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<font color="#004faf">All Classes</font></a>
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<font color="#004faf">Main Classes</font></a>
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<font color="#004faf">Annotated</font></a>
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<font color="#004faf">Grouped Classes</font></a>
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<font color="#004faf">Functions</font></a>
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</td>
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Window Geometry</h1>
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<h2> Overview
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</h2>
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<a name="1"></a><p> <a href="qwidget.html">QWidget</a> provides several functions that deal with a widget's
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geometry. Some of these functions operate on the pure client area
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(i.e. the window excluding the window frame), others include the
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window frame. The differentiation is done in a way that covers the
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most common usage transparently.
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<p> <center><table cellpadding="4" cellspacing="2" border="0">
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<tr bgcolor="#f0f0f0">
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<td valign="top"><strong>Including the window frame:
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<td valign="top">x(), y(), frameGeometry(), pos() and move()
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<tr bgcolor="#d0d0d0">
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<td valign="top"><strong>Excluding the window frame:</strong>
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<td valign="top">geometry(), width(), height(), rect() and size()
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</table></center>
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<p> Note that the distinction only matters for decorated top-level
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widgets. For all child widgets, the frame geometry is equal to the
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widget's client geometry.
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<p> This diagram shows most of the functions in use:
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<center><img src="geometry.png" alt="Geometry diagram"></center>
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<p> <h2> Unix/X11 peculiarities
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</h2>
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<a name="2"></a><p> On Unix/X11, a window does not have a frame until the window manager
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decorates it. This happens asynchronously at some point in time after
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calling show() and the first paint event the window receives: or it
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does not happen at all. Bear in mind that X11 is policy-free (others
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call it flexible). Thus you cannot make any safe assumption about the
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decoration frame your window will get. Basic rule: there's always one
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user who uses a window manager that breaks your assumption, and who
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will complain to you.
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<p> Furthermore, a toolkit cannot simply place windows on the screen. All
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Qt can do is to send certain hints to the window manager. The window
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manager, a separate process, may either obey, ignore or misunderstand
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them. Due to the partially unclear Inter-Client Communication
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Conventions Manual (ICCCM), window placement is handled quite
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differently in existing window managers.
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<p> X11 provides no standard or easy way to get the frame geometry once
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the window is decorated. Qt solves this problem with nifty heuristics
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and clever code that works on a wide range of window managers that
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exist today. Don't be surprised if you find one where frameGeometry()
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returns bogus results though.
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<p> Nor does X11 provide a way to maximize a window. The showMaximized()
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function in Qt therefore has to emulate the feature. Its result
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depends on the result of frameGeometry() and the capability of the
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window manager to do proper window placement, neither of which can be
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guaranteed.
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<p> <h2> Restoring a Window's Geometry
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</h2>
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<a name="3"></a><p> A common task in modern applications is to restore a window's geometry
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in a later session. On Windows, this is basically storing the result
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of geometry() and calling setGeometry() in the next session before
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calling show(). On X11, this won't work because an invisible window
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doesn't have a frame yet. The window manager would decorate the window
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later. When this happens, the window shifts towards the bottom/right
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corner of the screen depending on the size of the decoration frame. X
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theoretically provides a way to avoid this shift. Our tests have
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shown, though, that almost all window managers fail to implement this
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feature.
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<p> A workaround is to call setGeometry() after show(). This has the
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two disadvantages that the widget appears at a wrong place for a
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millisecond (results in flashing) and that currently only every
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second window manager gets it right. A safer solution is to store
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both pos() and size() and to restore the geometry using resize() and
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move() before calling show(), as demonstrated in the following
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example:
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<p> <pre>
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MyWidget* widget = new MyWidget
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...
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<a href="qpoint.html">QPoint</a> p = widget->pos(); // store position
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<a href="qsize.html">QSize</a> s = widget->size(); // store size
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...
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widget = new MyWidget;
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widget->resize( s ); // restore size
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widget->move( p ); // restore position
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widget->show(); // show widget
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</pre>
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<p> This method works on both MS-Windows and most existing X11 window
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managers.
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<p>
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<!-- eof -->
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<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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|
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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