How can I load local fonts dynamically?

[kyuranger]

I'm working on a program that runs on embedded Linux and supports multiple languages. I want to use different fonts for different languages, but I don't want to store all the font files as AvaloniaResources, which would significantly increase the size of the program.

The font files for all the different languages ​​I use total nearly 1GB, which is daunting.

Thus, I'm thinking of dynamically loading font files based on the current language. My program also supports dynamic language switching (without restarting the program).

So, I'm looking for a way to dynamically load local fonts, including unloading them after loading (to avoid unnecessary memory usage when switching languages).

However, I only found this discussion:
#13563

This discussion is very long and fragmented, and I can't piece together the individual responses. I'm also unsure if it meets my needs, nor am I sure the latest version of Avalonia includes an API that makes it easier to achieve my needs.

My idea is to check whether there is a font for the corresponding language before switching to a different language. If not, download it online or ask the user to provide the font file. This can minimize the size of the program.

So, I'm raising this discussion to learn how this can be achieved.

[Gillibald]

How do you ensure that the necessary fonts are present on the system? Maybe you could introduce multiple font packages like: https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Fonts.Inter/InterFontCollection.cs
and load them on demand.

Adding and removing collection works at runtime as long as fonts are loaded before they are referenced.

[kyuranger]

I'm not sure I understand your point.

But if, as you suggest, I encapsulate the fonts as a NuGet package and reference them, I think I'll run into the same problem I mentioned earlier: referencing too many fonts will make the program bulky. The font files for all the different languages ​​I use total nearly 1GB, which is daunting.

Furthermore, my program is used for industrial printing, and our competitors' programs all offer the ability to load custom fonts. While I don't plan to implement this feature in the short term, the requirement is similar to my current one, so I'll have to address it eventually.

[kyuranger]

How do you ensure that the necessary fonts are present on the system? Maybe you could introduce multiple font packages like: https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Fonts.Inter/InterFontCollection.cs and load them on demand.

Adding and removing collection works at runtime as long as fonts are loaded before they are referenced.

My idea is to check whether there is a font for the corresponding language before switching to a different language. If not, download it online or ask the user to provide the font file. This can minimize the size of the program.

[kyuranger]

Through the source files you provided, I found a way, but I am not sure whether it is stable and reliable, especially on embedded Linux.

MainWindow:

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="AvaloniaApplication1.MainWindow"
		xmlns:Local="using:AvaloniaApplication1"
		x:DataType="Local:ViewModel"
        Title="AvaloniaApplication1" FontFamily="{Binding FontFamily}">
	<TextBlock FontSize="100">Test Test Test</TextBlock>
</Window>

ViewModel:

using Avalonia.Media;
using CommunityToolkit.Mvvm.ComponentModel;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AvaloniaApplication1
{
    public partial class ViewModel:ObservableObject
    {
        public ViewModel()
        {
            FontManager.Current.AddFontCollection(new CustomFontCollection("MiSans"));
            FontFamily = new FontFamily("MiSans");
        }
        [ObservableProperty]
        FontFamily _FontFamily=FontFamily.Default;
    }
}

CustomFontCollection:

using Avalonia.Media.Fonts;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AvaloniaApplication1
{
    public sealed class CustomFontCollection : EmbeddedFontCollection
    {
        public CustomFontCollection(string fontName) : base(
            new Uri($"fonts:{fontName}", UriKind.Absolute),
            new Uri(System.IO.Path.Combine(AppContext.BaseDirectory, "Fonts"), UriKind.Absolute))
        {
        }
    }
}

At least it works on my computer (Windows 10).