switch to yeslogic-fontconfig-sys from servo-fontconfig

This allows setting the RUST_FONTCONFIG_DLOPEN environment variable
to dlopen fontconfig at runtime rather than linking it at build
time. This is helpful for cross compiling to Linux, particularly
because fontconfig has lots of C dependencies. Building a vendored
copy of fontconfig does not work as expected:
slint-ui#88

examples/plotter/Cargo.toml

@@ -15,11 +15,24 @@ name = "plotter"
 
 [dependencies]
 slint = { path = "../../api/rs/slint" }
-plotters = { version = "0.3.1", default-features = false, features = ["bitmap_backend", "surface_series"] }
+# TODO: switch to upstream plotters when https://github.com/38/plotters/pull/337 is merged
+plotters = { git = "https://github.com/Be-ing/plotters.git", branch = "font-kit-update", default-features = false, features = ["bitmap_backend", "surface_series"] }
 
 [build-dependencies]
 slint-build = { path = "../../api/rs/build" }
 
+[features]
+# This is required so plotters enables font-kit's source-fontconfig-dlopen feature
+# when building the workspace with `cargo build --workspace --all-features` on CI. This is because
+# `--workspace --all-features` enables i-slint-backend-gl and i-slint-compiler's fontconfig-dlopen
+# features. Without this, font-kit would fail to build because Cargo would activate the dlopen
+# feature of yeslogic-fontconfig-sys but not font-kit's source-fontconfig-dlopen feature.
+#
+# If you want to enable this feature apart from `--workspace --all-features`, set the environment
+# variable RUST_FONTCONFIG_DLOPEN=on to enable the fontconfig-dlopen features of
+# i-slint-backend-gl and i-slint-compiler.
+fontconfig-dlopen = ["plotters/fontconfig-dlopen"]
+
 # Remove the `#wasm#` to uncomment the wasm build.
 # This is commented out by default because we don't want to build it as a library by default
 # The CI has a script that does sed "s/#wasm# //" to generate the wasm build.

internal/backends/gl/Cargo.toml

@@ -20,6 +20,10 @@ path = "lib.rs"
 svg = ["resvg", "usvg", "tiny-skia"]
 wayland = ["winit/wayland", "glutin/wayland", "copypasta/wayland"]
 x11 = ["winit/x11", "glutin/x11", "copypasta/x11"]
+# dlopen fontconfig at runtime rather than link at build time.
+# useful for cross compiling
+# Using a vendored fontconfig C library does not work well, refer to Issue #88.
+fontconfig-dlopen = [ "font-kit/source-fontconfig-dlopen", "yeslogic-fontconfig-sys/dlopen" ]
 
 rtti = ["i-slint-core/rtti"]
 
@@ -70,9 +74,7 @@ winapi = { version = "0.3", features = ["dwrite"] }
 
 [target.'cfg(not(any(target_family = "windows", target_os = "macos", target_os = "ios", target_arch = "wasm32")))'.dependencies]
 libc = { version = "0.2" }
-# Require font-config from the system on Linux. Issue #88 indicates that the copy provided by servo-fontconfig may be incompatible
-# with distros at times.
-servo-fontconfig = { version = "0.5", features = [ "force_system_lib" ] }
+yeslogic-fontconfig-sys = "3.0.0"
 
 [target.'cfg(target_os = "macos")'.dependencies]
 cocoa = { version = "0.24.0" }

internal/backends/gl/build.rs

@@ -0,0 +1,10 @@
+// Copyright © SixtyFPS GmbH <[email protected]>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+fn main() {
+    println!("cargo:rerun-if-env-changed=RUST_FONTCONFIG_DLOPEN");
+    let dlopen = std::env::var("RUST_FONTCONFIG_DLOPEN").is_ok();
+    if dlopen {
+        println!("cargo:rustc-cfg=feature=\"fontconfig-dlopen\"");
+    }
+}

internal/backends/gl/fonts/fontconfig.rs

@@ -1,29 +1,58 @@
 // Copyright © SixtyFPS GmbH <[email protected]>
 // SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
 
-use fontconfig::fontconfig;
+use fontconfig_sys as ffi;
+use fontconfig_sys::ffi_dispatch;
+
+#[cfg(feature = "fontconfig-dlopen")]
+use ffi::statics::LIB;
+#[cfg(not(feature = "fontconfig-dlopen"))]
+use ffi::*;
 
 // This is duplicated in the slint-compiler's glyph embedding code
 pub fn find_families(requested_family: &str) -> Vec<String> {
     unsafe {
-        let config = fontconfig::FcInitLoadConfigAndFonts();
+        let config = ffi_dispatch!(feature = "fontconfig-dlopen", LIB, FcInitLoadConfigAndFonts,);
         let family_cstr = std::ffi::CString::new(requested_family).unwrap();
-        let pattern = fontconfig::FcNameParse(family_cstr.as_ptr() as *mut libc::c_uchar);
-        fontconfig::FcConfigSubstitute(std::ptr::null_mut(), pattern, fontconfig::FcMatchPattern);
-        fontconfig::FcDefaultSubstitute(pattern);
-        let mut sort_result = fontconfig::FcResultMatch;
-        let result_set =
-            fontconfig::FcFontSort(config, pattern, 1, std::ptr::null_mut(), &mut sort_result);
+        let pattern = ffi_dispatch!(
+            feature = "fontconfig-dlopen",
+            LIB,
+            FcNameParse,
+            family_cstr.as_ptr() as *mut libc::c_uchar
+        );
+        ffi_dispatch!(
+            feature = "fontconfig-dlopen",
+            LIB,
+            FcConfigSubstitute,
+            std::ptr::null_mut(),
+            pattern,
+            ffi::FcMatchPattern
+        );
+        ffi_dispatch!(feature = "fontconfig-dlopen", LIB, FcDefaultSubstitute, pattern);
+        let mut sort_result = ffi::FcResultMatch;
+        let result_set = ffi_dispatch!(
+            feature = "fontconfig-dlopen",
+            LIB,
+            FcFontSort,
+            config,
+            pattern,
+            1,
+            std::ptr::null_mut(),
+            &mut sort_result
+        );
 
         let mut families = Vec::new();
         for idx in 0..(*result_set).nfont {
             let mut raw_family_name = std::ptr::null_mut();
-            if fontconfig::FcPatternGetString(
+            if ffi_dispatch!(
+                feature = "fontconfig-dlopen",
+                LIB,
+                FcPatternGetString,
                 *(*result_set).fonts.offset(idx as isize),
                 b"family\0".as_ptr() as *const libc::c_char,
                 0,
-                &mut raw_family_name,
-            ) != fontconfig::FcResultMatch
+                &mut raw_family_name
+            ) != ffi::FcResultMatch
             {
                 continue;
             }
@@ -41,9 +70,9 @@ pub fn find_families(requested_family: &str) -> Vec<String> {
             }
         }
 
-        fontconfig::FcFontSetDestroy(result_set);
-        fontconfig::FcPatternDestroy(pattern);
-        fontconfig::FcConfigDestroy(config);
+        ffi_dispatch!(feature = "fontconfig-dlopen", LIB, FcFontSetDestroy, result_set);
+        ffi_dispatch!(feature = "fontconfig-dlopen", LIB, FcPatternDestroy, pattern);
+        ffi_dispatch!(feature = "fontconfig-dlopen", LIB, FcConfigDestroy, config);
         families
     }
 }

internal/compiler/Cargo.toml

@@ -20,6 +20,10 @@ path = "lib.rs"
 # Generators
 cpp = []
 rust = ["quote", "proc-macro2"]
+# dlopen fontconfig at runtime rather than link at build time.
+# useful for cross compiling
+# Using a vendored fontconfig C library does not work well, refer to Issue #88.
+fontconfig-dlopen = [ "yeslogic-fontconfig-sys/dlopen" ]
 
 # Support for proc_macro spans in the token (only useful for use within a proc macro)
 proc_macro_span = ["quote", "proc-macro2"]
@@ -61,9 +65,7 @@ usvg = "0.22"
 
 [target.'cfg(not(any(target_family = "windows", target_os = "macos", target_os = "ios", target_arch = "wasm32")))'.dependencies]
 libc = { version = "0.2" }
-# Require font-config from the system on Linux. Issue #88 indicates that the copy provided by servo-fontconfig may be incompatible
-# with distros at times.
-servo-fontconfig = { version = "0.5", features = [ "force_system_lib" ] }
+yeslogic-fontconfig-sys = "3.0.0"
 
 [dev-dependencies]
 i-slint-parser-test-macro = { path = "./parser-test-macro" }

internal/compiler/build.rs

@@ -6,6 +6,12 @@ use std::io::Write;
 use std::path::{Path, PathBuf};
 
 fn main() -> std::io::Result<()> {
+    println!("cargo:rerun-if-env-changed=RUST_FONTCONFIG_DLOPEN");
+    let dlopen = std::env::var("RUST_FONTCONFIG_DLOPEN").is_ok();
+    if dlopen {
+        println!("cargo:rustc-cfg=feature=\"fontconfig-dlopen\"");
+    }
+
     let mut library_dir = PathBuf::from(std::env::var_os("CARGO_MANIFEST_DIR").unwrap());
     library_dir.push("widgets");
 

internal/compiler/passes/embed_glyphs/fontconfig.rs

@@ -1,30 +1,59 @@
 // Copyright © SixtyFPS GmbH <[email protected]>
 // SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
 
-use fontconfig::fontconfig;
+use fontconfig_sys as ffi;
+use fontconfig_sys::ffi_dispatch;
 
-// This is duplicated from the GL backend
+#[cfg(feature = "fontconfig-dlopen")]
+use ffi::statics::LIB;
+#[cfg(not(feature = "fontconfig-dlopen"))]
+use ffi::*;
+
+// This is duplicated in the slint-compiler's glyph embedding code
 pub fn find_families(requested_family: &str) -> Vec<String> {
     #[allow(unsafe_code)]
     unsafe {
-        let config = fontconfig::FcInitLoadConfigAndFonts();
+        let config = ffi_dispatch!(feature = "fontconfig-dlopen", LIB, FcInitLoadConfigAndFonts,);
         let family_cstr = std::ffi::CString::new(requested_family).unwrap();
-        let pattern = fontconfig::FcNameParse(family_cstr.as_ptr() as *mut libc::c_uchar);
-        fontconfig::FcConfigSubstitute(std::ptr::null_mut(), pattern, fontconfig::FcMatchPattern);
-        fontconfig::FcDefaultSubstitute(pattern);
-        let mut sort_result = fontconfig::FcResultMatch;
-        let result_set =
-            fontconfig::FcFontSort(config, pattern, 1, std::ptr::null_mut(), &mut sort_result);
+        let pattern = ffi_dispatch!(
+            feature = "fontconfig-dlopen",
+            LIB,
+            FcNameParse,
+            family_cstr.as_ptr() as *mut libc::c_uchar
+        );
+        ffi_dispatch!(
+            feature = "fontconfig-dlopen",
+            LIB,
+            FcConfigSubstitute,
+            std::ptr::null_mut(),
+            pattern,
+            ffi::FcMatchPattern
+        );
+        ffi_dispatch!(feature = "fontconfig-dlopen", LIB, FcDefaultSubstitute, pattern);
+        let mut sort_result = ffi::FcResultMatch;
+        let result_set = ffi_dispatch!(
+            feature = "fontconfig-dlopen",
+            LIB,
+            FcFontSort,
+            config,
+            pattern,
+            1,
+            std::ptr::null_mut(),
+            &mut sort_result
+        );
 
         let mut families = Vec::new();
         for idx in 0..(*result_set).nfont {
             let mut raw_family_name = std::ptr::null_mut();
-            if fontconfig::FcPatternGetString(
+            if ffi_dispatch!(
+                feature = "fontconfig-dlopen",
+                LIB,
+                FcPatternGetString,
                 *(*result_set).fonts.offset(idx as isize),
                 b"family\0".as_ptr() as *const libc::c_char,
                 0,
-                &mut raw_family_name,
-            ) != fontconfig::FcResultMatch
+                &mut raw_family_name
+            ) != ffi::FcResultMatch
             {
                 continue;
             }
@@ -42,9 +71,9 @@ pub fn find_families(requested_family: &str) -> Vec<String> {
             }
         }
 
-        fontconfig::FcFontSetDestroy(result_set);
-        fontconfig::FcPatternDestroy(pattern);
-        fontconfig::FcConfigDestroy(config);
+        ffi_dispatch!(feature = "fontconfig-dlopen", LIB, FcFontSetDestroy, result_set);
+        ffi_dispatch!(feature = "fontconfig-dlopen", LIB, FcPatternDestroy, pattern);
+        ffi_dispatch!(feature = "fontconfig-dlopen", LIB, FcConfigDestroy, config);
         families
     }
 }