Resolve font family and style

[manfromarce]

Is it possible to use a font installed on the system (not necessarily part of standard font families) such as Calibri or Arial in bold and italic style if the exact font face name is not known? SixLabors.Fonts should be able to resolve the font but I can't initialize a VectSharp.Font with these parameters.

[arklumpus]

Hi, the two main issues with using system fonts in VectSharp are that there is no cross-platform "safe" way of finding the font files (as far as I'm aware), and that the library only supports fonts in raw TTF files.

If you're on Windows, you can try something like this:

FolderFontLibrary systemFonts = new FolderFontLibrary(@"C:\Windows\Fonts");

string[] fontNames = new[] { "Calibri", "Calibri Bold", "Arial Italic", "Cambria", "Cambria Regular", "Cambria Bold" };
foreach (string fontName in fontNames)
{
    FontFamily fontFamily = systemFonts.ResolveFontFamily(fontName);

    if (fontFamily.TrueTypeFile != null)
    {
        Console.WriteLine("'{0}' resolved as '{1}' ({2})", fontName, fontFamily.FamilyName, fontFamily.FileName);
    }
    else
    {
        Console.WriteLine("'{0}' not resolved!", fontName);
    }
}

That this can be rather fragile, for example this is the output I get on my PC:

'Calibri' resolved as 'Calibri' (C:\Windows\Fonts\calibri.ttf)
'Calibri Bold' resolved as 'Calibri Bold' (C:\Windows\Fonts\calibrib.ttf)
'Arial Italic' resolved as 'Arial Italic' (C:\Windows\Fonts\ariali.ttf)
'Cambria' resolved as 'Cambria Bold' (C:\Windows\Fonts\cambriab.ttf)
'Cambria Regular' not resolved!
'Cambria Bold' resolved as 'Cambria Bold' (C:\Windows\Fonts\cambriab.ttf)

Note how Cambria gets resolved as Cambria Bold... This is because the regular Cambria font is stored in C:\Windows\Fonts\cambria.ttc, which is not a plain TTF file; therefore, the closest TTF file that matches is the one for Cambria Bold.

On Linux, the font files may be in any subfolder of /usr/share/fonts or ~/.local/share/fonts (or potentially somewhere else), so it gets a bit more complicated:

string[] fontFolders = new string[] { "/usr/share/fonts", "~/.local/share/fonts" };

static IEnumerable<FolderFontLibrary> TraverseFolder(string folder)
{
    if (Directory.Exists(folder))
    {
        yield return new FolderFontLibrary(folder);

        foreach (string subfolder in Directory.GetDirectories(folder))
        {
            foreach (FolderFontLibrary subfolderLib in TraverseFolder(subfolder))
            {
                yield return subfolderLib;
            }
        }
    }
}

MultiFontLibrary systemFonts = new MultiFontLibrary(fontFolders.SelectMany(TraverseFolder));

string[] fontNames = new[] { "Ubuntu", "Ubuntu Bold", "DejaVu", "DejaVu Sans Bold", "DejaVu Serif", "DejaVu Serif Bold Italic" };
foreach (string fontName in fontNames)
{
    FontFamily fontFamily = systemFonts.ResolveFontFamily(fontName);

    if (fontFamily.TrueTypeFile != null)
    {
        Console.WriteLine("'{0}' resolved as '{1}' ({2})", fontName, fontFamily.FamilyName, fontFamily.FileName);
    }
    else
    {
        Console.WriteLine("'{0}' not resolved!", fontName);
    }
}

Which prints:

'Ubuntu' resolved as 'Ubuntu' (/usr/share/fonts/truetype/ubuntu/Ubuntu-R.ttf)
'Ubuntu Bold' resolved as 'Ubuntu Bold' (/usr/share/fonts/truetype/ubuntu/Ubuntu-B.ttf)
'DejaVu' not resolved!
'DejaVu Sans Bold' resolved as 'DejaVu Sans Bold' (/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf)
'DejaVu Serif' resolved as 'DejaVu Serif' (/usr/share/fonts/truetype/dejavu/DejaVuSerif.ttf)
'DejaVu Serif Bold Italic' resolved as 'DejaVu Serif Bold Italic' (/usr/share/fonts/truetype/dejavu/DejaVuSerif-BoldItalic.ttf)

On macOS, you can try something similar to Linux, but with a different set of folders:

string[] fontFolders = new string[] { "/System/Library/Fonts", "/Library/Fonts", "~/Library/Fonts" };

In any case, including the font files for the fonts you need together with your program will still be the best option... Is there any particular reason why you don't want to do that?

[manfromarce]

Hi, thank you for your answer.
I am trying to render DOCX documents using VectSharp because it has no native dependencies compared to SkiaSharp, and obviously I cannot include all possible fonts. In Open XML documents the font name and style attributes are specified separately (similar to HTML), such as Arial + bold or Arial Black (without explicit bold). In the first case, should "Bold" or "Italic" be appended to the font family like in your example? I am not sure if the name is always exactly like that.
Another problem is that if a font does not contain a style, ideally it should be simulated.

[arklumpus]

Sorry, I never replied to this... I'm afraid this kind of font resolution is quite beyond the scope of my library, but if you can create some sort of heuristic algorithm to match a font family name + font style to a specific TTF file, it should not be too hard to interface it with VectSharp (except that it still doesn't support TTC or OTF fonts). The heuristic itself won't be trivial, because font names can be weird (for example, there is in theory a distinction between italic and oblique, which is reflected in font family names, but in Word there is only one button to make text italic...).

Simulating font styles is also quite beyond what I can do, although again you could do some basic preprocessing before interfacing with VectSharp... For example, if you need a bold version of a font, you could both stroke and fill the text, while if you need an italicised version, you could apply a skew transform before drawing it.