Make it possible to build without the FemtoVG renderer

internal/backends/winit/Cargo.toml

@@ -19,7 +19,7 @@ path = "lib.rs"
 [features]
 wayland = ["winit/wayland", "glutin/wayland", "copypasta/wayland"]
 x11 = ["winit/x11", "glutin/x11", "copypasta/x11"]
-renderer-femtovg = []
+renderer-femtovg = ["femtovg", "fontdb", "libc", "servo-fontconfig", "winapi", "dwrote", "imgref", "unicode-script", "ttf-parser"]
 renderer-skia = ["skia-safe", "glow"]
 rtti = ["i-slint-core/rtti"]
 default = []
@@ -35,19 +35,21 @@ vtable = { version = "0.1.6", path = "../../../helper_crates/vtable" }
 cfg-if = "1"
 copypasta = { version = "0.8.1", default-features = false }
 derive_more = "0.99.5"
-femtovg = { version = "0.3.5" }
-fontdb = { version = "0.9.0", default-features = false }
-imgref = "1.6.1"
 lyon_path = "1.0"
 once_cell = "1.5"
 pin-weak = "1"
 rgb = "0.8.27"
 scoped-tls-hkt = "0.1"
-ttf-parser = "0.15.0" # Use the same version was femtovg's rustybuzz, to avoid duplicate crates
-unicode-script = "0.5.4" # Use the same version was femtovg's rustybuzz, to avoid duplicate crates
 winit = { version = "0.26", default-features = false }
 dark-light = "0.2.2"
 
+# For the FemtoVG renderer
+femtovg = { version = "0.3.5", optional = true }
+fontdb = { version = "0.9.0", optional = true, default-features = false }
+ttf-parser = { version = "0.15.0", optional = true } # Use the same version was femtovg's rustybuzz, to avoid duplicate crates
+unicode-script = { version = "0.5.4", optional = true } # Use the same version was femtovg's rustybuzz, to avoid duplicate crates
+imgref = { version = "1.6.1", optional = true }
+
 # For the Skia renderer
 skia-safe = { version = "0.53.0", optional = true, features = ["gl", "textlayout"] }
 glow = { version = "0.11", optional = true }
@@ -57,19 +59,21 @@ web-sys = { version = "0.3", features=["console", "WebGlContextAttributes", "Can
 wasm-bindgen = { version = "0.2" }
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
-fontdb = { version = "0.9.0", features = ["memmap", "fontconfig"] }
+fontdb = { version = "0.9.0", optional = true, features = ["memmap", "fontconfig"] }
 glutin = { version = "0.28", default-features = false }
 
+# For the FemtoVG renderer
 [target.'cfg(target_family = "windows")'.dependencies]
-dwrote = "0.11.0"
-winapi = { version = "0.3", features = ["dwrite"] }
+dwrote = { version = "0.11.0", optional = true }
+winapi = { version = "0.3", optional = true, features = ["dwrite"] }
 
 [target.'cfg(not(any(target_family = "windows", target_os = "macos", target_os = "ios", target_arch = "wasm32")))'.dependencies]
-libc = { version = "0.2" }
+libc = { version = "0.2", optional = true }
 # 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" ] }
+servo-fontconfig = { version = "0.5", optional = true, features = [ "force_system_lib" ] }
 
+# For the GL 
 [target.'cfg(target_os = "macos")'.dependencies]
 cocoa = { version = "0.24.0" }
 core-foundation = { version = "0.9.1" }

internal/backends/winit/lib.rs

@@ -53,6 +53,7 @@ mod renderer {
         fn component_destroyed(&self, component: i_slint_core::component::ComponentRef);
     }
 
+    #[cfg(feature = "renderer-femtovg")]
     pub(crate) mod femtovg;
     #[cfg(feature = "renderer-skia")]
     pub(crate) mod skia;
@@ -92,7 +93,8 @@ pub struct Backend {
 
 impl Backend {
     pub fn new(renderer_name: Option<&str>) -> Self {
-        let femtovg_factory = || {
+        #[cfg(feature = "renderer-femtovg")]
+        let (default_renderer, default_renderer_factory) = ("FemtoVG", || {
             i_slint_core::window::WindowInner::new(|window| {
                 GLWindow::<renderer::femtovg::FemtoVGRenderer>::new(
                     window,
@@ -101,10 +103,31 @@ impl Backend {
                 )
             })
             .into()
-        };
+        });
+        #[cfg(all(not(feature = "renderer-femtovg"), feature = "renderer-skia"))]
+        let (default_renderer, default_renderer_factory) = ("Skia", || {
+            i_slint_core::window::WindowInner::new(|window| {
+                GLWindow::<renderer::skia::SkiaRenderer>::new(
+                    window,
+                    #[cfg(target_arch = "wasm32")]
+                    "canvas".into(),
+                )
+            })
+            .into()
+        });
 
         let factory_fn = match renderer_name {
-            Some("gl") | Some("femtovg") | None => femtovg_factory,
+            #[cfg(feature = "renderer-femtovg")]
+            Some("gl") | Some("femtovg") => || {
+                i_slint_core::window::WindowInner::new(|window| {
+                    GLWindow::<renderer::femtovg::FemtoVGRenderer>::new(
+                        window,
+                        #[cfg(target_arch = "wasm32")]
+                        "canvas".into(),
+                    )
+                })
+                .into()
+            },
             #[cfg(feature = "renderer-skia")]
             Some("skia") => || {
                 i_slint_core::window::WindowInner::new(|window| {
@@ -116,12 +139,13 @@ impl Backend {
                 })
                 .into()
             },
+            None => default_renderer_factory,
             Some(renderer_name) => {
                 eprintln!(
-                    "slint winit: unrecognized renderer {}, falling back to FemtoVG",
-                    renderer_name
+                    "slint winit: unrecognized renderer {}, falling back to {}",
+                    renderer_name, default_renderer
                 );
-                femtovg_factory
+                default_renderer_factory
             }
         };
         Self { window_factory_fn: Mutex::new(Box::new(factory_fn)) }