Add X11-specific with_gtk_theme_variant option (#659)

src/platform/linux/mod.rs

@@ -45,6 +45,7 @@ pub struct PlatformSpecificWindowBuilderAttributes {
     pub class: Option<(String, String)>,
     pub override_redirect: bool,
     pub x11_window_type: x11::util::WindowType,
+    pub gtk_theme_variant: Option<String>,
 }
 
 lazy_static!(

src/platform/linux/x11/window.rs

@@ -272,6 +272,10 @@ impl UnownedWindow {
                 window.set_window_type(pl_attribs.x11_window_type).queue();
             }
 
+            if let Some(variant) = pl_attribs.gtk_theme_variant {
+                window.set_gtk_theme_variant(variant).queue();
+            }
+
             // set size hints
             {
                 let mut min_dimensions = window_attrs.min_dimensions;
@@ -457,6 +461,19 @@ impl UnownedWindow {
         )
     }
 
+    fn set_gtk_theme_variant(&self, variant: String) -> util::Flusher {
+        let hint_atom = unsafe { self.xconn.get_atom_unchecked(b"_GTK_THEME_VARIANT\0") };
+        let utf8_atom = unsafe { self.xconn.get_atom_unchecked(b"UTF8_STRING\0") };
+        let variant = CString::new(variant).expect("`_GTK_THEME_VARIANT` contained null byte");
+        self.xconn.change_property(
+            self.xwindow,
+            hint_atom,
+            utf8_atom,
+            util::PropMode::Replace,
+            variant.as_bytes(),
+        )
+    }
+
     #[inline]
     pub fn set_urgent(&self, is_urgent: bool) {
         let mut wm_hints = self.xconn.get_wm_hints(self.xwindow).expect("`XGetWMHints` failed");