Termux: unable to determine default font. Failed to locate font for family DejaVu Sans

[Quackdoc]

Bug Description

Cannot launch slint program (krokiet) on termux.

I am trying to run a program called krokiet on termux but it seems to fail due to font issues (Worth noting wayland is needed because when cross compiling for some reason it can't find the display server)

➜  ~ XDG_RUNTIME_DIR=$PREFIX/tmp WAYLAND_DISPLAY=wayland-2 XDG_DATA_DIRS=$PREFIX/glibc/share RUST_BACKTRACE=1 grun ./krokiet
03:26:35.195 [INFO] czkawka_core::common: App version: 8.0.0, release mode, rust 1.83.0 (2024-11-26), os Linux Unknown [aarch64 64-bit], 6 cpu/threads, features(0): []
thread 'main' panicked at /home/quack/.cargo/registry/src/index.crates.io-6f17d22bba15001f/i-slint-common-1.8.0/sharedfontdb.rs:165:13:
Unable to determine default font. Failed to locate font for family DejaVu Sans
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: i_slint_common::sharedfontdb::init_fontdb
   3: std::sys::thread_local::native::lazy::Storage<T,D>::initialize
   4: i_slint_core::graphics::image::svg::load_from_data
   5: i_slint_core::graphics::image::cache::ImageCache::load_image_from_embedded_data
   6: i_slint_core::graphics::image::load_image_from_embedded_data
   7: krokiet::slint_generatedMainWindow::InnerMainWindow::init
   8: krokiet::slint_generatedMainWindow::MainWindow::new
   9: krokiet::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Reproducible Code (if applicable)

No response

Environment Details

• Slint Version: 1.8
• Platform/OS: Android Termux
• Programming Language: Rust
• Backend/Renderer: winit software

Product Impact

How to test:

1. Build krokiet with cargo build --release --target aarch64-unknown-linux-gnu --no-default-features --features "winit_software"

2. copy to termux (setup with termux-x11)

3. launch sway termux-x11 :1 -xstartup "XDG_RUNTIME_DIR=$PREFIX/tmp sway"

4. try to launch the program XDG_RUNTIME_DIR=$PREFIX/tmp WAYLAND_DISPLAY=wayland-2 XDG_DATA_DIRS=$PREFIX/glibc/share RUST_BACKTRACE=1 grun ./krokiet

this bug prevents use of slint on termux.

[tronical]

This error message indicates that while fontconfig says the font for "Sans Serif" is "DejaVu Sans", that font can't be found in any directories that are scanned for fonts.

Where in your target environment for the krokiet process (sysroot?) are your fonts located?

[Quackdoc]

I have my font's located here /data/data/com.termux/files/usr/glibc/share/fonts/TTF/DejaVuSans.ttf $PREFIX = /data/data/com.termux/files/usr

[ogoffart]

Ideally we shouldn't panic in that case, but somehow return an error from run() or something like that.

[tronical]

Yes, that's #2556.

[tronical]

I'll convert this into a discussion, as this is most likely a setup issue. Happy to continue triaging there.

[Quackdoc]

I found this #4077 which had SLINT_DEFAULT_FONT set so I ran with XDG_RUNTIME_DIR=$PREFIX/tmp WAYLAND_DISPLAY=wayland-2 XDG_DATA_DIRS=$PREFIX/glibc/share SLINT_DEFAULT_FONT=$XDG_DATA_DIRS/fonts RUST_BACKTRACE=1 grun ./krokiet and the app did launch.

Perhaps the issue is simply that XDG_RUNTIME_DIR is not being considered?

[tronical]

Setting SLINT_DEFAULT_FONT to a directory will make Slint consider all families in that directory as the default font. That doesn't seem quite right to me, and it covers up the fact that font-config and fontdb aren't aligned on the directories.

What directories does your fonts.conf contain? Ideally it should refer to the paths in your $PREFIX.

[Quackdoc]

I am using grun which makes everything run from $PREFIX/glibc

➜  ~ cat $PREFIX/glibc/etc/fonts/fonts.conf
<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd">
<!-- /etc/fonts/fonts.conf file to configure system font access -->
<fontconfig>
	<description>Default configuration file</description>

<!--
	DO NOT EDIT THIS FILE.
	IT WILL BE REPLACED WHEN FONTCONFIG IS UPDATED.
	LOCAL CHANGES BELONG IN 'local.conf'.

	The intent of this standard configuration file is to be adequate for
	most environments.  If you have a reasonably normal environment and
	have found problems with this configuration, they are probably
	things that others will also want fixed.  Please submit any problems
	to the fontconfig issue tracking system located at fontconfig.org

	Note that the normal 'make install' procedure for fontconfig is to
	replace any existing fonts.conf file with the new version.  Place
	any local customizations in local.conf which this file references.

	Keith Packard
-->

<!-- Font directory list -->

	<dir>/system/fonts</dir>
	<dir>/data/data/com.termux/files/usr/glibc/share/fonts</dir>

	
	<dir prefix="xdg">fonts</dir>
	<!-- the following element will be removed in the future -->
	<dir>~/.fonts</dir>

<!--
  Accept deprecated 'mono' alias, replacing it with 'monospace'
-->
	<match target="pattern">
		<test qual="any" name="family">
			<string>mono</string>
		</test>
		<edit name="family" mode="assign" binding="same">
			<string>monospace</string>
		</edit>
	</match>

<!--
  Accept alternate 'sans serif' spelling, replacing it with 'sans-serif'
-->
	<match target="pattern">
		<test qual="any" name="family">
			<string>sans serif</string>
		</test>
		<edit name="family" mode="assign" binding="same">
			<string>sans-serif</string>
		</edit>
	</match>

<!--
  Accept deprecated 'sans' alias, replacing it with 'sans-serif'
-->
	<match target="pattern">
		<test qual="any" name="family">
			<string>sans</string>
		</test>
		<edit name="family" mode="assign" binding="same">
			<string>sans-serif</string>
		</edit>
	</match>
<!--
  Accept alternate 'system ui' spelling, replacing it with 'system-ui'
-->
	<match target="pattern">
		<test qual="any" name="family">
			<string>system ui</string>
		</test>
		<edit name="family" mode="assign" binding="same">
			<string>system-ui</string>
		</edit>
	</match>

<!--
  Load local system customization file
-->
	<include ignore_missing="yes">conf.d</include>

<!-- Font cache directory list -->

	<cachedir>/data/data/com.termux/files/usr/glibc/var/cache/fontconfig</cachedir>
	<cachedir prefix="xdg">fontconfig</cachedir>
	<!-- the following element will be removed in the future -->
	<cachedir>~/.fontconfig</cachedir>

	<config>
<!--
  Rescan configuration every 30 seconds when FcFontSetList is called
 -->
		<rescan>
			<int>30</int>
		</rescan>
	</config>

</fontconfig>