Add hooks for custom window decorations

This is a first use of the new hooks system, which allows customizing
cosmic-comp at compile-time.
In this case, the view() function of CosmicWindow / CosmicStack is
hooked and the hook can change what is rendered as the header bar.

Signed-off-by: Yureka <yuka@yuka.dev>

src/hooks.rs

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-3.0-only
+
+use crate::shell::element::stack::{
+    CosmicStackInternal, DefaultDecorations as DefaultStackDecorations, Message as StackMessage,
+};
+use crate::shell::element::window::{
+    CosmicWindowInternal, DefaultDecorations as DefaultWindowDecorations, Message as WindowMessage,
+};
+use std::sync::{Arc, OnceLock};
+
+/// An _unstable_ interface to customize cosmic-comp at compile-time by providing
+/// hooks to be run in specific code paths.
+#[derive(Default, Debug, Clone)]
+pub struct Hooks {
+    pub window_decorations:
+        Option<Arc<dyn Decorations<CosmicWindowInternal, WindowMessage> + Send + Sync>>,
+    pub stack_decorations:
+        Option<Arc<dyn Decorations<CosmicStackInternal, StackMessage> + Send + Sync>>,
+}
+
+pub static HOOKS: OnceLock<Hooks> = OnceLock::new();
+
+pub trait Decorations<Internal, Message>: std::fmt::Debug {
+    fn view(&self, state: &Internal) -> cosmic::Element<'_, Message>;
+}
+
+impl Decorations<CosmicWindowInternal, WindowMessage>
+    for Option<Arc<dyn Decorations<CosmicWindowInternal, WindowMessage> + Send + Sync>>
+{
+    fn view(&self, window: &CosmicWindowInternal) -> cosmic::Element<'_, WindowMessage> {
+        match self {
+            None => DefaultWindowDecorations.view(window),
+            Some(deco) => deco.view(window),
+        }
+    }
+}
+
+impl Decorations<CosmicStackInternal, StackMessage>
+    for Option<Arc<dyn Decorations<CosmicStackInternal, StackMessage> + Send + Sync>>
+{
+    fn view(&self, window: &CosmicStackInternal) -> cosmic::Element<'_, StackMessage> {
+        match self {
+            None => DefaultStackDecorations.view(window),
+            Some(deco) => deco.view(window),
+        }
+    }
+}

src/lib.rs

@@ -33,6 +33,7 @@ pub mod config;
 pub mod dbus;
 #[cfg(feature = "debug")]
 pub mod debug;
+pub mod hooks;
 pub mod input;
 mod logger;
 pub mod session;
@@ -103,7 +104,7 @@ impl State {
     }
 }
 
-pub fn run() -> Result<(), Box<dyn Error>> {
+pub fn run(hooks: crate::hooks::Hooks) -> Result<(), Box<dyn Error>> {
     let raw_args = RawArgs::from_args();
     let mut cursor = raw_args.cursor();
     let git_hash = option_env!("GIT_HASH").unwrap_or("unknown");
@@ -137,6 +138,10 @@ pub fn run() -> Result<(), Box<dyn Error>> {
 
     utils::rlimit::increase_nofile_limit();
 
+    // init hook globals
+    hooks::HOOKS.set(hooks)
+        .expect("Hooks global has already been initialized. Running multiple instances of COSMIC in one process is not supported.");
+
     // init event loop
     let mut event_loop = EventLoop::try_new().with_context(|| "Failed to initialize event loop")?;
     // init wayland

src/main.rs

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-3.0-only
 
 fn main() {
-    if let Err(err) = cosmic_comp::run() {
+    if let Err(err) = cosmic_comp::run(Default::default()) {
         tracing::error!("Error occured in main(): {}", err);
         std::process::exit(1);
     }

src/shell/element/stack.rs

@@ -4,6 +4,7 @@ use super::{
 };
 use crate::{
     backend::render::cursor::CursorState,
+    hooks::{Decorations, HOOKS},
     shell::{
         focus::target::PointerFocusTarget,
         grabs::{ReleaseMode, ResizeEdge},
@@ -1007,12 +1008,57 @@ impl Program for CosmicStackInternal {
     }
 
     fn view(&self) -> CosmicElement<'_, Self::Message> {
-        let windows = self.windows.lock().unwrap();
+        HOOKS.get().unwrap().stack_decorations.view(self)
-        if self.geometry.lock().unwrap().is_none() {
+    }
+
+    fn foreground(
+        &self,
+        pixels: &mut tiny_skia::PixmapMut<'_>,
+        damage: &[Rectangle<i32, Buffer>],
+        scale: f32,
+        theme: &Theme,
+    ) {
+        if self.group_focused.load(Ordering::SeqCst) {
+            let border = Rectangle::new(
+                (0, ((TAB_HEIGHT as f32 * scale) - scale).floor() as i32).into(),
+                (pixels.width() as i32, scale.ceil() as i32).into(),
+            );
+
+            let mut paint = tiny_skia::Paint::default();
+            let (b, g, r, a) = theme.cosmic().accent_color().into_components();
+            paint.set_color(tiny_skia::Color::from_rgba(r, g, b, a).unwrap());
+
+            for rect in damage {
+                if let Some(overlap) = rect.intersection(border) {
+                    pixels.fill_rect(
+                        tiny_skia::Rect::from_xywh(
+                            overlap.loc.x as f32,
+                            overlap.loc.y as f32,
+                            overlap.size.w as f32,
+                            overlap.size.h as f32,
+                        )
+                        .unwrap(),
+                        &paint,
+                        Default::default(),
+                        None,
+                    )
+                }
+            }
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct DefaultDecorations;
+
+impl Decorations<CosmicStackInternal, Message> for DefaultDecorations {
+    fn view(&self, stack: &CosmicStackInternal) -> cosmic::Element<'_, Message> {
+        let windows = stack.windows.lock().unwrap();
+        if stack.geometry.lock().unwrap().is_none() {
             return iced_widget::row(Vec::new()).into();
         };
-        let active = self.active.load(Ordering::SeqCst);
+        let active = stack.active.load(Ordering::SeqCst);
-        let group_focused = self.group_focused.load(Ordering::SeqCst);
+        let group_focused = stack.group_focused.load(Ordering::SeqCst);
 
         let elements = vec![
             cosmic_widget::icon::from_name("window-stack-symbolic")
@@ -1057,7 +1103,8 @@ impl Program for CosmicStackInternal {
                 )
                 .id(SCROLLABLE_ID.clone())
                 .force_visible(
-                    self.scroll_to_focus
+                    stack
+                        .scroll_to_focus
                         .load(Ordering::SeqCst)
                         .then_some(active),
                 )
@@ -1079,7 +1126,7 @@ impl Program for CosmicStackInternal {
         } else {
             Radius::from([8.0, 8.0, 0.0, 0.0])
         };
-        let group_focused = self.group_focused.load(Ordering::SeqCst);
+        let group_focused = stack.group_focused.load(Ordering::SeqCst);
 
         iced_widget::row(elements)
             .height(TAB_HEIGHT as u16)
@@ -1109,42 +1156,6 @@ impl Program for CosmicStackInternal {
             }))
             .into()
     }
-
-    fn foreground(
-        &self,
-        pixels: &mut tiny_skia::PixmapMut<'_>,
-        damage: &[Rectangle<i32, Buffer>],
-        scale: f32,
-        theme: &Theme,
-    ) {
-        if self.group_focused.load(Ordering::SeqCst) {
-            let border = Rectangle::new(
-                (0, ((TAB_HEIGHT as f32 * scale) - scale).floor() as i32).into(),
-                (pixels.width() as i32, scale.ceil() as i32).into(),
-            );
-
-            let mut paint = tiny_skia::Paint::default();
-            let (b, g, r, a) = theme.cosmic().accent_color().into_components();
-            paint.set_color(tiny_skia::Color::from_rgba(r, g, b, a).unwrap());
-
-            for rect in damage {
-                if let Some(overlap) = rect.intersection(border) {
-                    pixels.fill_rect(
-                        tiny_skia::Rect::from_xywh(
-                            overlap.loc.x as f32,
-                            overlap.loc.y as f32,
-                            overlap.size.w as f32,
-                            overlap.size.h as f32,
-                        )
-                        .unwrap(),
-                        &paint,
-                        Default::default(),
-                        None,
-                    )
-                }
-            }
-        }
-    }
 }
 
 impl IsAlive for CosmicStack {

src/shell/element/window.rs

@@ -1,5 +1,6 @@
 use crate::{
     backend::render::cursor::CursorState,
+    hooks::{Decorations, HOOKS},
     shell::{
         focus::target::PointerFocusTarget,
         grabs::{ReleaseMode, ResizeEdge},
@@ -554,11 +555,20 @@ impl Program for CosmicWindowInternal {
     }
 
     fn view(&self) -> cosmic::Element<'_, Self::Message> {
+        HOOKS.get().unwrap().window_decorations.view(self)
+    }
+}
+
+#[derive(Debug)]
+pub struct DefaultDecorations;
+
+impl Decorations<CosmicWindowInternal, Message> for DefaultDecorations {
+    fn view(&self, win: &CosmicWindowInternal) -> cosmic::Element<'_, Message> {
         let mut header = cosmic::widget::header_bar()
-            .title(self.last_title.lock().unwrap().clone())
+            .title(win.last_title.lock().unwrap().clone())
             .on_drag(Message::DragStart)
             .on_close(Message::Close)
-            .focused(self.window.is_activated(false))
+            .focused(win.window.is_activated(false))
             .on_double_click(Message::Maximize)
             .on_right_click(Message::Menu)
             .is_ssd(true);