#1456 Font fallback support

[Xen Kuo]

Will Scintilla have a plan to support the font fallback feature? I've did some document check, seems it isn't supported now.

[Neil Hodgson]

What exactly do you mean by "font fallback"? How does this differ from the platform's font matching? Which platform are you using?

[Xen Kuo]

Hi Neil, sorry for the late response.
I think the "font fallback" is a general concept in web development. For example, I can set multiple font types to an application, like font type A and font type B, then a symbol is not included in type A, the application will render it using type B, this is the "font fallback" I mentioned.

If type B doesn't include it as well, then fallback to platform's font. Just sometimes the platform matched font is not the one user preferred, so the application level font fallback is better.

This is not platform dependent.

[Neil Hodgson]

The implementation is platform dependent as it depends on detecting font absence and high level font APIs commonly 'pretend' that every font request succeeds by substituting a font that is available.

For example, this Win32 code returns S_OK producing a valid pTextFormat despite there being no font called "Xen Kuo" on the system.

pIDWriteFactory->CreateTextFormat(
    L"Xen Kuo",
    nullptr,
    DWRITE_FONT_WEIGHT_NORMAL,
    DWRITE_FONT_STYLE_NORMAL,
    DWRITE_FONT_STRETCH_NORMAL,
    13.3,
    L"en-us",
    &pTextFormat);

[Neil Hodgson]

Closing as incomplete.

[Zufu Liu]

Maybe custom fallback font created by IDWriteFontFallbackBuilder?
https://learn.microsoft.com/en-us/windows/win32/api/dwrite_2/nn-dwrite_2-idwritefontfallbackbuilder