Charts

UniOffice cannot create a native PowerPoint chart on a slide. The presentation package has no chart constructor - AddChart exists only on a spreadsheet drawing - so a chart on a slide has to be rendered to an image first and added as a picture. The example does that with UniChart and UniPDF’s renderer.

Neither approach gives you a chart PowerPoint will let the reader edit and refresh. If that matters, the chart has to be authored in the template and the program limited to filling the placeholders around it.

Rendering a chart onto a slide

chart := &unichart.PieChart{
    Values: []dataset.Value{
        {Value: 5, Label: "Blue"},
        {Value: 4, Label: "Gray"},
    },
}
chart.SetHeight(500)

c := creator.New()
if err := c.Draw(creator.NewChart(chart)); err != nil {
    log.Fatalf("failed to draw chart: %v", err)
}
if err := c.WriteToFile("output.pdf"); err != nil {
    log.Fatalf("failed to write output file: %v", err)
}

That produces a one-page PDF. The example then renders page 1 to a PNG with render.NewImageDevice(), trims the surrounding whitespace with its own cropImage and findBoundingBox helpers, and hands the result to the ordinary picture path:

img, err := common.ImageFromFile("preview.png")
iref, err := ppt.AddImage(img)
pic := slide.AddImage(iref)
pic.Properties().SetWidth(2 * measurement.Inch)
pic.Properties().SetHeight(iref.RelativeHeight(2 * measurement.Inch))

From AddImage onwards this is the same code as the images guide. The chart is a PNG like any other.

What this needs

Three UniDoc modules: unioffice/v2 for the presentation, unipdf/v5 for the creator and the renderer, and unichart for the chart itself. Both UniOffice and UniPDF check their own metered license, so init sets the key twice, once through each package.

The rendered image resolution comes from device.OutputWidth, which the example sets to 2000. Too low and the chart is soft on a projector; too high and the PNG dominates the file size of the deck.

Limitations

The chart is a picture. It does not scale as vector art, its text is not selectable or searchable, and text extraction will not see the labels. The .pptx grows by the size of the PNG for every chart on every slide.

Rendering goes through a PDF on disk. c.WriteToFile and the image device both touch the filesystem, so the working directory has to be writable and the intermediate output.pdf and preview.png are left behind.

ppt.Charts() and slide.GetChartSpaceByRelId return the ChartSpace of charts that were already in an opened file. They are read paths into the DrawingML chart schema, not a way to build one.

Run the example

The example builds a pie chart with seven slices, renders it, crops it, adds it to a new slide two inches wide, and writes output.pptx alongside the intermediate output.pdf and preview.png.

git clone https://github.com/unidoc/unioffice-examples.git
cd unioffice-examples/presentation/chart
go run main.go

If this is your first time using UniOffice, follow the getting started guide to create an API key and set up your development environment.