Using XRRSetCrtcConfig

[Manuel Schneider]

Hello, for a project at my university I need to use the libxrandr to change the screensettings. I use XRRSetCrtConfig to apply the settings. But after applying the settings several times there is just a little rectangle left on my monitors, where something of the desktop is displayed. Is there something missing? I use the code below.

regards
////////////////////////////////////////////////////
 XGrabServer(_display);

  // First get a useful representation
  unsigned int width, height;
  QStringList modeAsStrings = _ui->comboBox->currentText().split("x", QString::SkipEmptyParts);
  width = modeAsStrings.at(0).toInt();
  height = modeAsStrings.at(1).toInt();

  // Find a mode that matches the string
  RRMode m1,m2;
  for (int i = 0; i < _outputMap[_monitor]->nmode; ++i){
    if ( width == _modeMap[_outputMap[_monitor]->modes[i]]->width
         && height == _modeMap[_outputMap[_monitor]->modes[i]]->height )
      m1 = _modeMap[_outputMap[_monitor]->modes[i]]->id;
  }
  for (int i = 0; i < _outputMap[_beamer]->nmode; ++i){
    if ( width == _modeMap[_outputMap[_beamer]->modes[i]]->width
         && height == _modeMap[_outputMap[_beamer]->modes[i]]->height )
      m2 = _modeMap[_outputMap[_beamer]->modes[i]]->id;
  }

  qDebug()  << _modeMap[m1]->width << _modeMap[m1]->height;
  qDebug()  << _modeMap[m2]->width << _modeMap[m2]->height;



  /* values from xrandr */
  float dpi = (25.4 * DisplayHeight(_display, 0)) / DisplayHeightMM(_display, 0);
  int widthMM =  (int) ((25.4 * width) / dpi);
  int heightMM = (int) ((25.4 * height) / dpi);

  // Set screensize
  XRRSetScreenSize(_display, DefaultRootWindow(_display),
                 width, height,
                 widthMM, heightMM);

  // Apply the modes
  XRRSetCrtcConfig(_display,
                   _screenResources,
                   _outputMap[_monitor]->crtc,
                   CurrentTime,
                   0, 0,
                   m1,
                   RR_Rotate_0,
                   &_monitor,
                   1);

  XRRSetCrtcConfig(_display,
                   _screenResources,
                   _outputMap[_beamer]->crtc,
                   CurrentTime,
                   0, 0,
                   m2,
                   RR_Rotate_0,
                   &_beamer,
                   1);


  XUngrabServer(_display);

/////////////////////////////////////////
-- 
Mit freundlichem Gruß
 Manuel Schneider