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| 31 | </td>
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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>Window Geometry</h1>
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| 33 |
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| 34 |
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| 35 | <h2> Overview
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| 36 | </h2>
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| 37 | <a name="1"></a><p> <a href="qwidget.html">QWidget</a> provides several functions that deal with a widget's
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| 38 | geometry. Some of these functions operate on the pure client area
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| 39 | (i.e. the window excluding the window frame), others include the
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| 40 | window frame. The differentiation is done in a way that covers the
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| 41 | most common usage transparently.
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| 42 | <p> <center><table cellpadding="4" cellspacing="2" border="0">
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| 43 | <tr bgcolor="#f0f0f0">
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| 44 | <td valign="top"><strong>Including the window frame:
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| 45 | <td valign="top">x(), y(), frameGeometry(), pos() and move()
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| 46 | <tr bgcolor="#d0d0d0">
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| 47 | <td valign="top"><strong>Excluding the window frame:</strong>
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| 48 | <td valign="top">geometry(), width(), height(), rect() and size()
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| 49 | </table></center>
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| 50 | <p> Note that the distinction only matters for decorated top-level
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| 51 | widgets. For all child widgets, the frame geometry is equal to the
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| 52 | widget's client geometry.
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| 53 | <p> This diagram shows most of the functions in use:
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| 54 | <center><img src="geometry.png" alt="Geometry diagram"></center>
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| 55 | <p> <h2> Unix/X11 peculiarities
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| 56 | </h2>
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| 57 | <a name="2"></a><p> On Unix/X11, a window does not have a frame until the window manager
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| 58 | decorates it. This happens asynchronously at some point in time after
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| 59 | calling show() and the first paint event the window receives: or it
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| 60 | does not happen at all. Bear in mind that X11 is policy-free (others
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| 61 | call it flexible). Thus you cannot make any safe assumption about the
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| 62 | decoration frame your window will get. Basic rule: there's always one
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| 63 | user who uses a window manager that breaks your assumption, and who
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| 64 | will complain to you.
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| 65 | <p> Furthermore, a toolkit cannot simply place windows on the screen. All
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| 66 | Qt can do is to send certain hints to the window manager. The window
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| 67 | manager, a separate process, may either obey, ignore or misunderstand
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| 68 | them. Due to the partially unclear Inter-Client Communication
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| 69 | Conventions Manual (ICCCM), window placement is handled quite
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| 70 | differently in existing window managers.
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| 71 | <p> X11 provides no standard or easy way to get the frame geometry once
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| 72 | the window is decorated. Qt solves this problem with nifty heuristics
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| 73 | and clever code that works on a wide range of window managers that
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| 74 | exist today. Don't be surprised if you find one where frameGeometry()
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| 75 | returns bogus results though.
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| 76 | <p> Nor does X11 provide a way to maximize a window. The showMaximized()
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| 77 | function in Qt therefore has to emulate the feature. Its result
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| 78 | depends on the result of frameGeometry() and the capability of the
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| 79 | window manager to do proper window placement, neither of which can be
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| 80 | guaranteed.
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| 81 | <p> <h2> Restoring a Window's Geometry
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| 82 | </h2>
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| 83 | <a name="3"></a><p> A common task in modern applications is to restore a window's geometry
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| 84 | in a later session. On Windows, this is basically storing the result
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| 85 | of geometry() and calling setGeometry() in the next session before
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| 86 | calling show(). On X11, this won't work because an invisible window
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| 87 | doesn't have a frame yet. The window manager would decorate the window
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| 88 | later. When this happens, the window shifts towards the bottom/right
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| 89 | corner of the screen depending on the size of the decoration frame. X
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| 90 | theoretically provides a way to avoid this shift. Our tests have
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| 91 | shown, though, that almost all window managers fail to implement this
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| 92 | feature.
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| 93 | <p> A workaround is to call setGeometry() after show(). This has the
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| 94 | two disadvantages that the widget appears at a wrong place for a
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| 95 | millisecond (results in flashing) and that currently only every
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| 96 | second window manager gets it right. A safer solution is to store
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| 97 | both pos() and size() and to restore the geometry using resize() and
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| 98 | move() before calling show(), as demonstrated in the following
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| 99 | example:
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| 100 | <p> <pre>
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| 101 | MyWidget* widget = new MyWidget
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| 102 | ...
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| 103 | <a href="qpoint.html">QPoint</a> p = widget->pos(); // store position
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| 104 | <a href="qsize.html">QSize</a> s = widget->size(); // store size
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| 105 | ...
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| 106 | widget = new MyWidget;
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| 107 | widget->resize( s ); // restore size
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| 108 | widget->move( p ); // restore position
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| 109 | widget->show(); // show widget
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| 110 | </pre>
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| 111 |
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| 112 | <p> This method works on both MS-Windows and most existing X11 window
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| 113 | managers.
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| 114 | <p>
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| 115 | <!-- eof -->
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| 116 | <p><address><hr><div align=center>
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| 118 | <td>Copyright © 2007
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| 119 | <a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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| 120 | <td align=right><div align=right>Qt 3.3.8</div>
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