You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
116 lines
5.8 KiB
116 lines
5.8 KiB
14 years ago
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
|
||
|
|
<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/opengl-x11-overlays.doc:36 -->
|
||
|
|
<html>
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
|
||
|
|
<title>How to use X11 overlays with the Qt OpenGL extension</title>
|
||
|
|
<style type="text/css"><!--
|
||
|
|
fn { margin-left: 1cm; text-indent: -1cm; }
|
||
|
|
a:link { color: #004faf; text-decoration: none }
|
||
|
|
a:visited { color: #672967; text-decoration: none }
|
||
|
|
body { background: #ffffff; color: black; }
|
||
|
|
--></style>
|
||
|
|
</head>
|
||
|
|
<body>
|
||
|
|
|
||
|
|
<table border="0" cellpadding="0" cellspacing="0" width="100%">
|
||
|
|
<tr bgcolor="#E5E5E5">
|
||
|
|
<td 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="annotated.html">
|
||
|
|
<font color="#004faf">Annotated</font></a>
|
||
|
|
| <a href="groups.html">
|
||
|
|
<font color="#004faf">Grouped Classes</font></a>
|
||
|
|
| <a href="functions.html">
|
||
|
|
<font color="#004faf">Functions</font></a>
|
||
|
|
</td>
|
||
|
|
<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>How to use X11 overlays with the Qt OpenGL extension</h1>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
<p> X11 overlays are a powerful mechanism for drawing
|
||
|
|
annotations etc., on top of an image without destroying it, thus saving
|
||
|
|
a great deal of image rendering time. For more information, consult the highly
|
||
|
|
recommended book <em>OpenGL Programming for the X Window System</em> (Mark
|
||
|
|
Kilgard, Addison Wesley Developers Press 1996).
|
||
|
|
<p> <b>Warning:</b> From version 5.0 onwards, the Qt OpenGL Extension includes
|
||
|
|
direct support for the use of OpenGL overlays. For many uses of
|
||
|
|
overlays, this makes the technique described below redundant. See the
|
||
|
|
<a href="opengl-overlay-example.html">overlay</a> example program. The
|
||
|
|
following is a discussion on how to use non-QGL widgets in overlay
|
||
|
|
planes.
|
||
|
|
<p> In the typical case, X11 overlays can easily be used together with the
|
||
|
|
current version of Qt and the Qt OpenGL Extension. The following
|
||
|
|
requirements apply:
|
||
|
|
<p> <ol type=1>
|
||
|
|
<li> Your X server and graphics card/hardware must support overlays.
|
||
|
|
For many X servers, overlay support can be turned on with
|
||
|
|
a configuration option; consult your X server installation
|
||
|
|
documentation.
|
||
|
|
<p> <li> Your X server must (be configured to) use an overlay visual as the
|
||
|
|
default visual. Most modern X servers do this, since this has the
|
||
|
|
added advantage that pop-up menus, overlapping windows etc., will
|
||
|
|
<em>not</em> destroy underlying images in the main plane, thereby
|
||
|
|
avoiding expensive redraws.
|
||
|
|
<p> <li> The best (deepest) visual for OpenGL rendering is in the main
|
||
|
|
plane. This is the normal case. Typically, X servers that support
|
||
|
|
overlays provide a 24 bit deep TrueColor visual in the main plane,
|
||
|
|
and an 8 bit PseudoColor (default) visual in the overlay plane.
|
||
|
|
</ol>
|
||
|
|
<p> The provided example program <a href="opengl-overlay-example.html">X11
|
||
|
|
overlay</a> will check for these and report if anything is wrong.
|
||
|
|
See <a href="#x11visuals">About X11 Visuals</a>, below for more
|
||
|
|
information.
|
||
|
|
<p> <h2> How it works
|
||
|
|
</h2>
|
||
|
|
<a name="1"></a><p> Given the above, a <a href="qglwidget.html">QGLWidget</a> will by default use the main plane
|
||
|
|
visual, while all other widgets will use the overlay visual. Thus, we
|
||
|
|
can place a normal widget on top of the QGLWidget, and do drawing on
|
||
|
|
it, without destroying the image in the OpenGL window. In other words,
|
||
|
|
we can use all the drawing capabilities of <a href="qpainter.html">QPainter</a> to draw the
|
||
|
|
annotations, rubberbands, etc. For the typical use of overlays,
|
||
|
|
this is much easier than using OpenGL for rendering the annotations.
|
||
|
|
<p> An overlay plane has a specific color called the transparent
|
||
|
|
color. Pixels drawn in this color will not be visible; instead the
|
||
|
|
underlying OpenGL image will show through. In the example program
|
||
|
|
<a href="opengl-overlay-example.html">X11 overlay</a>, the file
|
||
|
|
<tt>main.cpp</tt> contains a routine that returns a <a href="qcolor.html">QColor</a> containing the
|
||
|
|
transparent color. For the overlay widget, you will typically want to
|
||
|
|
set the background color to the transparent color, so that the OpenGL
|
||
|
|
image shows through except where explicitly overpainted.
|
||
|
|
<p> Note: to use this technique, you must not use the "ManyColor" or
|
||
|
|
"TrueColor" ColorSpec for <a href="qapplication.html">QApplication</a>, because this will force
|
||
|
|
the normal Qt widgets to use a TrueColor visual, which will typically
|
||
|
|
be in the main plane, not in the overlay plane as desired.
|
||
|
|
<p> <a name="x11visuals"></a>
|
||
|
|
<h2> About X11 visuals
|
||
|
|
</h2>
|
||
|
|
<a name="2"></a><p> The utilities directory contains two small programs that can help you
|
||
|
|
determine the capabilities of your X server. These programs are from
|
||
|
|
the OpenGL book mentioned above, see utilities/NOTICE for copyright
|
||
|
|
information. The full set of example programs from this book is
|
||
|
|
available at <a href="ftp://ftp.sgi.com/pub/opengl/opengl_for_x/">ftp://ftp.sgi.com/pub/opengl/opengl_for_x/</a>.
|
||
|
|
<p> <tt>glxvisuals</tt> will list all the GL-capable visuals the X server
|
||
|
|
provides, together with the depth and other GL-specific information
|
||
|
|
for each. Note especially the column "lvl"; a number in this column
|
||
|
|
means the visual is in an overlay plane.
|
||
|
|
<p> <tt>sovinfo</tt> will list all available visuals, and provides special
|
||
|
|
transparency information for overlay visuals.
|
||
|
|
<p> The <a href="opengl-overlay-example.html">X11 overlay</a> example
|
||
|
|
program will output what visual is used for the normal Qt widgets, and
|
||
|
|
what visual is used by the <a href="qglwidget.html">QGLWidget</a>.
|
||
|
|
<p>
|
||
|
|
<!-- eof -->
|
||
|
|
<p><address><hr><div align=center>
|
||
|
|
<table width=100% cellspacing=0 border=0><tr>
|
||
|
|
<td>Copyright © 2007
|
||
|
|
<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
|
||
|
|
<td align=right><div align=right>Qt 3.3.8</div>
|
||
|
|
</table></div></address></body>
|
||
|
|
</html>
|