QwtPlotRenderer renderDocument() 匯出圖片

 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);  }}