Integrate libadwaita for the gtk backend (#792)

* When using gtk as the backend, link libadwaita

* Update c.zig

* Use libadwaita's theme manager for gtk

* update the documentation for window-theme

* build: add libadwaita to the nix devshell

* forgot to properly import libadwaita

* apprt/gtk: adwaita style change

---------

Co-authored-by: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>

build.zig

@@ -814,6 +814,7 @@ fn addDeps(
 
             .gtk => {
                 step.linkSystemLibrary2("gtk4", dynamic_link_opts);
+                step.linkSystemLibrary2("adwaita-1", dynamic_link_opts);
             },
         }
     }

nix/devshell.nix

@@ -28,6 +28,7 @@
 , freetype
 , glib
 , gtk4
+, libadwaita
 , harfbuzz
 , libpng
 , libGL
@@ -59,6 +60,7 @@ let
     libXi
     libXrandr
 
+    libadwaita
     gtk4
     glib
   ];
@@ -120,6 +122,7 @@ in mkShell rec {
     libXrandr
 
     # Only needed for GTK builds
+    libadwaita
     gtk4
     glib
   ];

src/apprt/gtk/App.zig

@@ -52,6 +52,9 @@ running: bool = true,
 pub fn init(core_app: *CoreApp, opts: Options) !App {
     _ = opts;
 
+    // Initialize libadwaita
+    c.adw_init();
+
     // Load our configuration
     var config = try Config.load(core_app.alloc);
     errdefer config.deinit();
@@ -63,6 +66,16 @@ pub fn init(core_app: *CoreApp, opts: Options) !App {
         }
     }
 
+    // Set the style based on our configuration file
+    c.adw_style_manager_set_color_scheme(
+        c.adw_style_manager_get_default(),
+        switch (config.@"window-theme") {
+            .system => c.ADW_COLOR_SCHEME_PREFER_LIGHT,
+            .dark => c.ADW_COLOR_SCHEME_FORCE_DARK,
+            .light => c.ADW_COLOR_SCHEME_FORCE_LIGHT,
+        },
+    );
+
     // The "none" cursor is used for hiding the cursor
     const cursor_none = c.gdk_cursor_new_from_name("none", null);
     errdefer if (cursor_none) |cursor| c.g_object_unref(cursor);

src/apprt/gtk/c.zig

@@ -1,5 +1,6 @@
 const c = @cImport({
     @cInclude("gtk/gtk.h");
+    @cInclude("libadwaita-1/adwaita.h");
 });
 
 pub usingnamespace c;

src/config/Config.zig

@@ -378,7 +378,7 @@ keybind: Keybinds = .{},
 /// also be set to "light" or "dark" to force a specific theme regardless
 /// of the system settings.
 ///
-/// This is currently only supported on macOS.
+/// This is currently only supported on macOS and linux.
 @"window-theme": WindowTheme = .system,
 
 /// The initial window size. This size is in terminal grid cells by default.