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<title>Qt 4.3: Window Geometry</title>
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<td width="1"> </td><td class="postheader" valign="center"><a href="index.html"><font color="#004faf">Home</font></a> · <a href="classes.html"><font color="#004faf">All Classes</font></a> · <a href="mainclasses.html"><font color="#004faf">Main Classes</font></a> · <a href="groups.html"><font color="#004faf">Grouped Classes</font></a> · <a href="modules.html"><font color="#004faf">Modules</font></a> · <a href="functions.html"><font color="#004faf">Functions</font></a></td>
<td align="right" valign="top" width="230"><a href="http://www.trolltech.com"><img src="images/trolltech-logo.png" align="right" width="203" height="32" border="0" /></a></td></tr></table><h1 align="center">Window Geometry<br /><small></small></h1>
<p><a href="qwidget.html">QWidget</a> provides several functions that deal with a widget's geometry. Some of these functions operate on the pure client area (i.e. the window excluding the window frame), others include the window frame. The differentiation is done in a way that covers the most common usage transparently.</p>
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<li><b>Including the window frame:</b> <a href="qwidget.html#x-prop">x()</a>, <a href="qwidget.html#y-prop">y()</a>, <a href="qwidget.html#frameGeometry-prop">frameGeometry()</a>, <a href="qwidget.html#pos-prop">pos()</a>, and <a href="qwidget.html#pos-prop">move()</a>.</li>
<li><b>Excluding the window frame:</b> <a href="qwidget.html#geometry-prop">geometry()</a>, <a href="qwidget.html#width-prop">width()</a>, <a href="qwidget.html#height-prop">height()</a>, <a href="qwidget.html#rect-prop">rect()</a>, and <a href="qwidget.html#size-prop">size()</a>.</li>
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<p>Note that the distinction only matters for decorated top-level widgets. For all child widgets, the frame geometry is equal to the widget's client geometry.</p>
<p>This diagram shows most of the functions in use:</p>
<p align="center"><img src="images/geometry.png" alt="Geometry diagram" /></p><p>Topics:</p>
<ul><li><a href="#x11-peculiarities">X11 Peculiarities</a></li>
<li><a href="#restoring-a-window-s-geometry">Restoring a Window's Geometry</a></li>
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<a name="x11-peculiarities"></a>
<h3>X11 Peculiarities</h3>
<p>On X11, a window does not have a frame until the window manager decorates it. This happens asynchronously at some point in time after calling <a href="qwidget.html#show">QWidget::show</a>() and the first paint event the window receives, or it does not happen at all. Bear in mind that X11 is policy-free (others call it flexible). Thus you cannot make any safe assumption about the decoration frame your window will get. Basic rule: There's always one user who uses a window manager that breaks your assumption, and who will complain to you.</p>
<p>Furthermore, a toolkit cannot simply place windows on the screen. All Qt can do is to send certain hints to the window manager. The window manager, a separate process, may either obey, ignore or misunderstand them. Due to the partially unclear Inter-Client Communication Conventions Manual (ICCCM), window placement is handled quite differently in existing window managers.</p>
<p>X11 provides no standard or easy way to get the frame geometry once the window is decorated. Qt solves this problem with nifty heuristics and clever code that works on a wide range of window managers that exist today. Don't be surprised if you find one where <a href="qwidget.html#frameGeometry-prop">QWidget::frameGeometry</a>() returns wrong results though.</p>
<p>Nor does X11 provide a way to maximize a window. <a href="qwidget.html#showMaximized">QWidget::showMaximized</a>() has to emulate the feature. Its result depends on the result of <a href="qwidget.html#frameGeometry-prop">QWidget::frameGeometry</a>() and the capability of the window manager to do proper window placement, neither of which can be guaranteed.</p>
<a name="restoring-a-window-s-geometry"></a>
<h3>Restoring a Window's Geometry</h3>
<p>Since version 4.2, Qt provides functions that saves and restores a window's geometry and state for you. <a href="qwidget.html#saveGeometry">QWidget::saveGeometry</a>() saves the window geometry and maximized/fullscreen state, while <a href="qwidget.html#restoreGeometry">QWidget::restoreGeometry</a>() restores it. The restore function also checks if the restored geometry is outside the available screen geometry, and modifies it as appropriate if it is.</p>
<p>The rest of this document describes how to save and restore the geometry using the geometry properties. On Windows, this is basically storing the result of <a href="qwidget.html#geometry-prop">QWidget::geometry</a>() and calling <a href="qwidget.html#geometry-prop">QWidget::setGeometry</a>() in the next session before calling <a href="qwidget.html#show">show()</a>. On X11, this won't work because an invisible window doesn't have a frame yet. The window manager will decorate the window later. When this happens, the window shifts towards the bottom/right corner of the screen depending on the size of the decoration frame. Although X provides a way to avoid this shift, most window managers fail to implement this feature.</p>
<p>A workaround is to call <a href="qwidget.html#geometry-prop">setGeometry()</a> after <a href="qwidget.html#show">show()</a>. This has the two disadvantages that the widget appears at a wrong place for a millisecond (results in flashing) and that currently only every second window manager gets it right. A safer solution is to store both <a href="qwidget.html#pos-prop">pos()</a> and <a href="qwidget.html#size-prop">size()</a> and to restore the geometry using <a href="qwidget.html#size-prop">QWidget::resize</a>() and <a href="qwidget.html#pos-prop">move()</a> before calling <a href="qwidget.html#show">show()</a>, as demonstrated in the following code snippets (from the <a href="mainwindows-application.html">Application</a> example):</p>
<pre> void MainWindow::readSettings()
{
QSettings settings("Trolltech", "Application Example");
QPoint pos = settings.value("pos", QPoint(200, 200)).toPoint();
QSize size = settings.value("size", QSize(400, 400)).toSize();
resize(size);
move(pos);
}
void MainWindow::writeSettings()
{
QSettings settings("Trolltech", "Application Example");
settings.setValue("pos", pos());
settings.setValue("size", size());
}</pre>
<p>This method works on Windows, Mac OS X, and most X11 window managers.</p>
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