Get Warning Callbacks for Font Substitution

Overview

Aspose.Slides for C++ allows you to receive warning callbacks for font substitution when a required font isn’t available on the machine during rendering. These callbacks help diagnose issues with missing or inaccessible fonts.

Enable Warning Callbacks

Aspose.Slides for C++ provides straightforward APIs for receiving warning callbacks when rendering presentation slides. Follow these steps to configure warning callbacks:

1. Create a custom callback class that implements the IWarningCallback interface to handle warnings.
2. Set the warning callback using option classes such as RenderingOptions, PdfOptions, HtmlOptions, and others.
3. Load a presentation that uses a font not available on the target machine.
4. Generate a slide thumbnail or export the presentation to observe the effect.

Custom Warning Callback Class:

#include <Warnings/IWarningCallback.h>

class FontWarningHandler : public IWarningCallback
{
public:
    ReturnAction Warning(SharedPtr<IWarningInfo> warning) override;
};

ReturnAction FontWarningHandler::Warning(SharedPtr<IWarningInfo> warning)
{
    if (warning->get_WarningType() == WarningType::DataLoss)
    {
        Console::WriteLine(warning->get_Description());
    }

    return ReturnAction::Continue;
}

// Example output:
//
// Font will be substituted from XYZ to {Calibri,Cambria Math,MS Gothic,Gulim,Arial Unicode,SimSun,Segoe UI Symbol}}

Generate a Slide Thumbnail:

// Set up a warning callback to handle font-related warnings during slide rendering.
auto options = MakeObject<RenderingOptions>();
options->set_WarningCallback(MakeObject<FontWarningHandler>());

// Load the presentation from the specified file path.
auto presentation = MakeObject<Presentation>(u"sample.pptx");
    
// Generate a thumbnail image for each slide in the presentation.
for(auto&& slide : presentation->get_Slides())
{
    // Get the slide thumbnail image using the specified rendering options.
    auto image = slide->GetImage(options);
    // ...

    image->Dispose();
}

presentation->Dispose();

Export to PDF Format:

// Set up a warning callback to handle font-related warnings during PDF export.
auto options = MakeObject<PdfOptions>();
options->set_WarningCallback(MakeObject<FontWarningHandler>());

// Load the presentation from the specified file path.
auto presentation = MakeObject<Presentation>(u"sample.pptx");

// Export the presentation as PDF.
auto stream = MakeObject<MemoryStream>();
presentation->Save(stream, SaveFormat::Pdf, options);
// ...

stream->Dispose();
presentation->Dispose();

Export to HTML Format:

// Set up a warning callback to handle font-related warnings during HTML export.
auto options = MakeObject<HtmlOptions>();
options->set_WarningCallback(MakeObject<FontWarningHandler>());

// Load the presentation from the specified file path.
auto presentation = MakeObject<Presentation>(u"sample.pptx");

// Export the presentation in HTML format.
auto stream = MakeObject<MemoryStream>();
presentation->Save(stream, SaveFormat::Html, options);
// ...

stream->Dispose();
presentation->Dispose();