QwtPlotRenderer renderDocument() 导出图片

 void MainWindow::exportDocument()
{
#ifndef QT_NO_PRINTER
  QString fileName = "bode.pdf";
#else
  QString fileName = "bode.png";
#endif

#ifndef QT_NO_FILEDIALOG
  const QList<QByteArray> imageFormats =  
  QImageWriter::supportedImageFormats();

  QStringList filter;
  filter += "PDF Documents (*.pdf)";
#ifndef QWT_NO_SVG
  filter += "SVG Documents (*.svg)";
#endif
  filter += "Postscript Documents (*.ps)";

  if ( imageFormats.size() > 0 )
  {
  QString imageFilter("Images (");
  for ( int i = 0; i < imageFormats.size(); i++ )
  {
  if ( i > 0 )
  imageFilter += " ";
  imageFilter += "*.";
  imageFilter += imageFormats[i];
  }
  imageFilter += ")";

  filter += imageFilter;
  }

  fileName = QFileDialog::getSaveFileName(
  this, "Export File Name", fileName,
  filter.join(";;"), NULL, QFileDialog::DontConfirmOverwrite);
#endif

  if ( !fileName.isEmpty() )
  {
  QwtPlotRenderer renderer;

  // flags to make the document look like the widget
  renderer.setDiscardFlag(QwtPlotRenderer::DiscardBackground, false);
  renderer.setLayoutFlag(QwtPlotRenderer::KeepFrames, true);

  renderer.renderDocument(d_plot, fileName, QSizeF(300, 200), 85);
  }
}