OS font lookup not working for some text

[dweymouth]

Checklist

• I have searched the issue tracker for open issues that relate to the same problem, before opening a new one.
• This issue only relates to a single bug. I will open new issues for any other problems.

Describe the bug

The ability to look up suitable fonts from the OS to display glyphs not in the bundled font works well for most text (including CJK), but there are still some strings that don't work with this and display the ? box placeholder glyph even if fonts are available on the OS to display them properly.

For more context see dweymouth/supersonic#756

How to reproduce

Run the example code

Screenshots

No response

Example code

package main

import (
	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/widget"
)

func main() {
	a := app.New()
	w := a.NewWindow("Hello World")

	w.SetContent(widget.NewLabel("𝕿𝖍𝖊 𝕸𝖆𝖑𝖉𝖔𝖗𝖔𝖗 𝕮𝖍𝖆𝖓𝖙𝖘: 𝕺𝖑𝖉 𝕺𝖈𝖊𝖆𝖓"))
	w.ShowAndRun()
}

Fyne version

develop

Go compiler version

1.25

Operating system and version

macOS

Additional Information

No response

[andydotxyz]

Can you share the font that it should have found so we know what is / isn't being found correctly?

[dweymouth]

I'm not sure how to figure out the font that the OS / browser / any other app is using to display a particular text string. The reporter of the issue in Supersonic said the Roboto font should have them

[psy-q]

It seems these are math symbols and should be in plenty of (reasonably Unicode-complete) fonts. I did find them in Roboto and suspect they're in Noto as well. The code points in question are in the original Supersonic issue linked above.

[redawl]

Interesting. These render correctly on Gentoo linux with the builtin fyne font:

[andydotxyz]

I am finding that the OS lookup does work for this. On my system it is using "Adwaita Mono" as the found font.

I used a small bit of code that asks the underlying gotext fontscan library:

	fm := fontscan.NewFontMap(log.Default())
	err = fm.UseSystemFonts("")

	str := "𝕿𝖍𝖊 𝕸𝖆𝖑𝖉𝖔𝖗𝖔𝖗 𝕮𝖍𝖆𝖓𝖙𝖘: 𝕺𝖑𝖉 𝕺𝖈𝖊𝖆𝖓"
	fx := fm.ResolveFace(rune(str[1]))
	log.Println("F", fx.Describe().Family)

(that's "github.com/go-text/typesetting/fontscan")

These render correctly on Gentoo linux with the builtin fyne font:

I don't think it's actually finding it in our builtin fonts.

[andydotxyz]

I did find them in Roboto and suspect they're in Noto as well.

Don't seem to be in Noto - which is what we use.

I confirmed this by checking that no Noto glyphs match at: https://fonts.google.com/noto/fonts?preview.text=%F0%9D%96%8D

[andydotxyz]

@dweymouth I'm going to say it looks like the issue is not that those characters are not working, but that the computer reporting it has a setup we don't fully support - i.e. the right font is not found (or is otherwise overlooked?).

If they can run the test script above we may understand if gotext cannot find a face on their setup.

[dweymouth]

@psy-q would you be able to run the Go test code here #6016 (comment) on your system where it is not displaying that album name properly?

[psy-q]

On the Mac I get:

2025/12/02 10:49:44 using system font dirs ["/Library/Fonts" "/System/Library/Fonts" "/Users/rca/Library/Fonts"]
2025/12/02 10:49:44 No font matched for aspect {0 0 0}, script , and rune U+009D (�) -> searching by script coverage only
2025/12/02 10:49:44 No font matched for script  and rune U+009D (�) -> returning arbitrary face
2025/12/02 10:49:44 F Arial Unicode MS

It's not showing the runes in the terminal output either, of course. I installed Roboto but it still didn't find them.

It seems my copy of Roboto on this machine (downloaded from Google themselves) indeed doesn't have them. Noto Sans Math does have them, but the Go test script did not find them in there:

[psy-q]

I faffed around a little with an LLM and got this:

package main

import (
	"log"

	"github.com/go-text/typesetting/fontscan"
	"github.com/go-text/typesetting/language"
)

func main() {
	fm := fontscan.NewFontMap(log.Default())
	err := fm.UseSystemFonts("")
	if err != nil {
		log.Fatal(err)
	}

	str := "𝕿𝖍𝖊 𝕸𝖆𝖑𝖉𝖔𝖗𝖔𝖗 𝕮𝖍𝖆𝖓𝖙𝖘: 𝕺𝖑𝖉 𝕺𝖈𝖊𝖆𝖓"
	runes := []rune(str)

	// Auto-detect script from first character and set it
	script := language.LookupScript(runes[0])
	fm.SetScript(script)

	// Now resolve font for a character
	fx := fm.ResolveFace(runes[0])
	log.Println("Font:", fx.Describe().Family)
}

This way it resolves Noto Sans Math correctly on its own. The glyphs are in the "Zyyy" (undetermined) script.