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Plot Export - QwtPlotRenderer

QwtPlotRenderer provides functionality to export plots to various file formats, supporting image files (PNG, JPG, etc.), PDF, SVG vector formats, and print output.

Main Features

Features

  • ✅ Multiple export formats: Supports PNG, JPG, BMP, PDF, SVG, PS, etc.
  • ✅ Resolution control: Configurable DPI resolution for exported images
  • ✅ Size settings: Customizable export dimensions or millimeter units
  • ✅ Layout options: Option to ignore titles, legends, and other components during export

Usage

1. Export to Image File

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#include <QwtPlotRenderer>

QwtPlotRenderer renderer;

// Export to PNG
renderer.renderDocument(plot, "plot.png", QSize(800, 600), 300);  // 300 DPI

// Export to JPG
renderer.renderDocument(plot, "plot.jpg", QSize(800, 600), 150);

// Export to BMP
renderer.renderDocument(plot, "plot.bmp", QSize(800, 600));

// File format is automatically determined by extension

2. Export to PDF

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// Export to PDF
renderer.renderDocument(plot, "plot.pdf", QSizeF(200, 150), 300);  // 200x150 mm, 300 DPI

// PDF supports vector graphics, suitable for high-resolution printing

3. Export to SVG

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// Export to SVG vector format
renderer.renderDocument(plot, "plot.svg", QSizeF(200, 150));

// SVG advantages:
// - Vector graphics, lossless scaling
// - Smaller file size
// - Can be viewed in browsers

4. Export to QImage/QPixmap

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// Export as QImage
QSize size(800, 600);
QImage image = renderer.renderToImage(plot, size, 300);  // 300 DPI

// Export as QPixmap
QPixmap pixmap = renderer.renderToPixmap(plot, size, 300);

// Can be used for in-application display or further processing

5. Export Options

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// Set export layout options
renderer.setDiscardFlag(QwtPlotRenderer::DiscardTitle, true);     // Ignore title
renderer.setDiscardFlag(QwtPlotRenderer::DiscardLegend, true);    // Ignore legend
renderer.setDiscardFlag(QwtPlotRenderer::DiscardFooter, true);    // Ignore footer
renderer.setDiscardFlag(QwtPlotRenderer::DiscardCanvasBackground, true);  // Ignore canvas background

// Set frame options
renderer.setDiscardFlag(QwtPlotRenderer::DiscardFrames, true);    // Ignore border frames

// Restore defaults
renderer.resetDiscardFlags();

6. Print Function

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#include <QPrinter>

// Print to printer
QPrinter printer(QPrinter::HighResolution);
printer.setOutputFileName("print.pdf");  // Or use printer.printerName()

renderer.renderDocument(plot, &printer);

// Or directly use QwtPlot's print method
plot->print(printer);

7. Using Millimeter Units for Size

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// Specify size in millimeter units
QSizeF sizeMm(200, 150);  // 200mm x 150mm
renderer.renderDocument(plot, "plot.pdf", sizeMm, 300);  // 300 DPI

Export Format Comparison

Format Advantages Disadvantages Use Cases
PNG Lossless compression, transparency support Larger file size Web sharing, screenshots
JPG Small file size, widely supported Lossy compression, no transparency Photo-like charts
PDF Vector, high resolution Requires PDF reader Printing, documents
SVG Vector, editable Complex graphics render slowly Web pages, editing
BMP Lossless, simple Very large file size Specific software

Export Option Enum

Option Description
DiscardTitle Ignore title
DiscardLegend Ignore legend
DiscardFooter Ignore footer
DiscardCanvasBackground Ignore canvas background
DiscardFrames Ignore borders

Core Method Summary

Method Description
renderDocument() Export to file
renderToImage() Export as QImage
renderToPixmap() Export as QPixmap
setDiscardFlag() Set discard option
resetDiscardFlags() Reset discard options

Export Recommendations

  • Use PDF or high-resolution PNG (300 DPI) for printing
  • Use SVG or PNG for web pages
  • Use PDF or SVG for document embedding
  • Use PNG or JPG for screenshot sharing

Related Examples

  • Export functionality demo: examples/2D/barchart