/****************************************************************************** $Id: qt/main.cpp   3.2.3   edited May 13 09:08 $**** Example application showing how to use Qt and Qt OpenGL Extension on an ** X11 overlay visual **** Copyright (C) 1999 by Trolltech AS.  All rights reserved.**** This file is part of an example program for Qt.  This example** program may be used, distributed and modified without limitation.*******************************************************************************/#include <qapplication.h>#include "gearwidget.h"#include "rubberbandwidget.h"#if defined(Q_WS_X11)#include <X11/Xlib.h>#endifQColor findOverlayTransparentColor(){    QColor invalidColor;#if defined(Q_WS_X11)    Display* appDisplay;    Visual* appVisual;    // The static methods are called 'App' in Qt 2.x#if QT_VERSION < 200    appDisplay = QPaintDevice::x__Display();    appVisual = (Visual*)QPaintDevice::x11Visual();#else    appDisplay = QPaintDevice::x11AppDisplay();    appVisual = (Visual*)QPaintDevice::x11AppVisual();#endif    qDebug( "Default Visual ID: 0x%x", (int)XVisualIDFromVisual(appVisual) );    typedef struct OverlayProp {	long  visual;	long  type;	long  value;	long  layer;    } OverlayProp;    QWidget* rootWin = QApplication::desktop();    if ( !rootWin )	return invalidColor; // Should not happen    Atom overlayVisualsAtom = XInternAtom( appDisplay, 					   "SERVER_OVERLAY_VISUALS", True );    if ( overlayVisualsAtom == None ) {	warning( "Server has no overlay visuals" );	return invalidColor;    }    Atom actualType;    int actualFormat;    ulong nItems;    ulong bytesAfter;    OverlayProp* overlayProp;    int res = XGetWindowProperty( appDisplay, QApplication::desktop()->winId(),				  overlayVisualsAtom, 0, 10000, False, 				  overlayVisualsAtom, &actualType, 				  &actualFormat, &nItems, &bytesAfter,				  (uchar**)&overlayProp );    if ( res != Success || actualType != overlayVisualsAtom 	 || actualFormat != 32 || nItems < 4 ) {	warning( "Failed to get overlay visual property from server" );	return invalidColor;    }    for ( uint i = 0; i < nItems/4; i++ ) {	if ( (VisualID)overlayProp[i].visual == XVisualIDFromVisual(appVisual)	     && overlayProp[i].type == 1 )	    return QColor( qRgb( 1, 2, 3 ), overlayProp[i].value );    }    qWarning( "Default visual is not in overlay plane" );    return invalidColor;#else // defined(Q_WS_X11)    qWarning( "Wrong window system - Only X11 has overlay support." );    return invalidColor;#endif}int main( int argc, char **argv ){    QApplication::setColorSpec( QApplication::CustomColor );    QApplication a( argc, argv );    if ( !QGLFormat::hasOpenGL() ) {	qWarning( "This system has no OpenGL support. Exiting." );	return -1;    }    QColor transparentColor = findOverlayTransparentColor();    if ( !transparentColor.isValid() ) {	qWarning( "Failed to get transparent color for overlay. Exiting." );	return -1;    }    QWidget top;    a.setMainWidget( &top );    top.setGeometry( 50, 50, 600, 400 );    // Make an OpenGL widget. It will use the deepest visual available    // (typically a TrueColor visual), which typically is in the normal layer.    GearWidget g( &top );    g.setGeometry( 20, 20, 560, 360 );    // Put the rubberband widget (which uses the default, i.e. overlay visual)    // on top of the OpenGL widget:    RubberbandWidget r( transparentColor, &top );    r.setGeometry( 20, 20, 560, 360 );    top.show();    return a.exec();}