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106 lines
5.3 KiB
106 lines
5.3 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/examples/opengl/overlay_x11/overlay_x11.doc:1 -->
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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>OpenGL Overlay X11 Example</title>
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<font color="#004faf">All Classes</font></a>
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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>OpenGL Overlay X11 Example</h1>
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<p>
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<b>Warning:</b> From version 5.0 onwards, the Qt OpenGL Extension includes
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direct support for use of OpenGL overlays. For many uses of overlays,
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this makes the technique described below redundant. See the <a href="opengl-overlay-example.html">overlay</a> example program. The
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following is a discussion on how to use non-QGL widgets in overlay
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planes.
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<p> Overlayrubber: An example program showing how to use Qt and Qt OpenGL
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Extension with X11 overlay visuals.
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<p> See <tt>$QTDIR/examples/opengl/overlay_x11</tt> for the source code.
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<p> Background information for this example can be found in the
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information on <a href="opengl-x11-overlays.html">overlays</a>.
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<p> The example program has three main parts:
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<p> <ol type=1>
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<li> <em>GearWidget</em> - a normal, simple <a href="qglwidget.html">QGLWidget</a>. This renders the usual
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gears. It has been modified to print a debug message every time it
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redraws (renders) itself. Thus, you can easily confirm that drawing in
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the overlay plane does not cause redrawings in the main plane where
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the QGLWidget resides.
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<p> <li> <em>RubberbandWidget</em> - Very simple standard (non-GL) Qt widget that
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implements rubberband drawing. Designed for use in an overlay plane.
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It takes the plane's transparent color as a constructor argument and
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uses that for its background color. Thus, the widget itself will be
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invisible, only the rubberbands it draws will be visible.
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<p> <li> <em>main.cpp</em> Creates a GearWidget and a Rubberbandwidget and puts the
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latter on top of the former. Contains a routine that checks that the
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default visual is in an overlay plane, and returns the transparent
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color of that plane.
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</ol>
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<p> <h2> Running the Example
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</h2>
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<a name="1"></a><p> Start the <tt>overlayrubber</tt> executable. Click and drag with the left
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mouse button to see rubberband drawing. Observe that the <a href="qglwidget.html">QGLWidget</a>
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does not redraw itself (no redraw debug messages are output), and yet
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the image is not destroyed. Marvel at the coolness of X11 overlays!
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<p> <h2> Using this technique in a real application
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</h2>
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<a name="2"></a><p> For clarity, this example program has been kept very simple. Here are
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some hints for real application usage:
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<p> <ul>
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<p> <li> <em>All normal widgets are in the overlay plane.</em> This means that you
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can put all kinds of Qt widgets (your own or standard Qt widgets) on
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top of the OpenGL image (widget), e.g. pushbuttons etc., and they can
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be moved, resized, or removed without destroying the OpenGL image.
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<p> <li> <em>Using with geometry management.</em> The <a href="qlayout.html">QLayout</a> classes don't permit
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putting one widget (the overlay) on top of another (the OpenGL
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widget); that would defy the whole purpose of the automatic layout.
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The solution is to add just one of them to the QLayout object. Have it
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keep a pointer to the other (i.e. the <a href="qglwidget.html">QGLWidget</a> knows about its
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overlay widget or vice versa). Implement the resizeEvent() method of
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the widget you put in the layout, and make it call setGeometry() on
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the other widget with its own geometry as parameters, thus keeping the
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two widgets' geometries synchronized.
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<p> <li> <em>Using together with <a href="qpalette.html">QPalette</a> and <a href="qcolorgroup.html">QColorGroup</a>.</em> Instead of the
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simplistic setBackgroundColor( transparentColor ), you can
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use Qt's QPalette system to make your overlay widgets use
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transparent color for what you want. This way, the normal Qt widgets
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can be used as overlays for fancy effects. Just create a palette for
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them with the transparent color for the relevant color roles, e.g.
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Background and Base, in the Normal and/or Active modes. This way, you
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can create see-through QPushButtons etc.
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</ul>
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<p> <p>See also <a href="opengl-examples.html">OpenGL Examples</a>.
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<p><address><hr><div align=center>
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<td>Copyright © 2007
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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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