Add rendering pipeline for client surfaces via OutputDamageTracker

- Create render module using Smithay's desktop::space::render_output
  for damage-tracked frame rendering to the Winit backend window
- Store backend and damage_tracker in CalloopData so the Winit event
  callback can trigger rendering on Redraw events
- Send initial xdg toplevel configure on first commit so clients can
  begin drawing
- Send frame callbacks after each render so clients schedule redraws

crates/wrsrvd/src/handlers/compositor.rs

@@ -7,6 +7,7 @@ use smithay::{
     wayland::{
         buffer::BufferHandler,
         compositor::{CompositorClientState, CompositorHandler, CompositorState},
+        seat::WaylandFocus,
         shm::{ShmHandler, ShmState},
     },
 };
@@ -44,6 +45,22 @@ impl CompositorHandler for WayRay {
     fn commit(&mut self, surface: &WlSurface) {
         trace!(?surface, "surface commit");
         smithay::backend::renderer::utils::on_commit_buffer_handler::<Self>(surface);
+
+        // If this surface belongs to an xdg toplevel that hasn't received
+        // its initial configure yet, send it now so the client can start
+        // drawing.
+        if let Some(window) = self
+            .space
+            .elements()
+            .find(|w| w.wl_surface().map(|s| s.into_owned()) == Some(surface.clone()))
+            .cloned()
+        {
+            if let Some(toplevel) = window.toplevel() {
+                if !toplevel.is_initial_configure_sent() {
+                    toplevel.send_configure();
+                }
+            }
+        }
     }
 }
 

crates/wrsrvd/src/main.rs

@@ -1,5 +1,6 @@
 mod errors;
 mod handlers;
+mod render;
 mod state;
 
 use std::sync::Arc;
@@ -11,8 +12,8 @@ use crate::state::WayRay;
 use miette::Result;
 use smithay::{
     backend::{
-        renderer::gles::GlesRenderer,
-        winit::{self, WinitEvent},
+        renderer::{damage::OutputDamageTracker, gles::GlesRenderer},
+        winit::{self, WinitEvent, WinitGraphicsBackend},
     },
     output::{Mode, Output, PhysicalProperties, Subpixel},
     reexports::wayland_server::Display,
@@ -25,6 +26,8 @@ use tracing::info;
 struct CalloopData {
     state: WayRay,
     display: Display<WayRay>,
+    backend: WinitGraphicsBackend<GlesRenderer>,
+    damage_tracker: OutputDamageTracker,
 }
 
 fn main() -> Result<()> {
@@ -118,7 +121,7 @@ fn main() -> Result<()> {
 
     // Insert the Winit event loop as a calloop source.
     loop_handle
-        .insert_source(winit_event_loop, move |event, _, _data| match event {
+        .insert_source(winit_event_loop, move |event, _, data| match event {
             WinitEvent::Resized { size, scale_factor } => {
                 info!(?size, scale_factor, "window resized");
             }
@@ -129,7 +132,11 @@ fn main() -> Result<()> {
                 // Input handling is Task 7 -- ignore for now.
             }
             WinitEvent::Redraw => {
-                // Rendering is Task 6 -- ignore for now.
+                render::render_output_frame(
+                    &mut data.state,
+                    &mut data.backend,
+                    &mut data.damage_tracker,
+                );
             }
             WinitEvent::CloseRequested => {
                 info!("close requested, shutting down");
@@ -138,10 +145,15 @@ fn main() -> Result<()> {
         })
         .map_err(|e| errors::WayRayError::EventLoop(Box::new(e.error)))?;
 
-    // Keep a handle to the backend (needed for rendering in Task 6).
-    let _backend = backend;
+    // Create a damage tracker for efficient rendering.
+    let damage_tracker = OutputDamageTracker::from_output(&output);
 
-    let mut calloop_data = CalloopData { state, display };
+    let mut calloop_data = CalloopData {
+        state,
+        display,
+        backend,
+        damage_tracker,
+    };
 
     info!("entering main event loop");
 

crates/wrsrvd/src/render.rs

@@ -0,0 +1,102 @@
+use smithay::{
+    backend::{
+        renderer::{
+            damage::OutputDamageTracker,
+            element::texture::TextureRenderElement,
+            gles::{GlesRenderer, GlesTexture},
+        },
+        winit::WinitGraphicsBackend,
+    },
+    desktop::{Window, space::render_output},
+};
+use tracing::warn;
+
+use crate::state::WayRay;
+
+/// Dark grey clear color for the compositor background.
+const CLEAR_COLOR: [f32; 4] = [0.1, 0.1, 0.1, 1.0];
+
+/// Render the compositor space to the Winit backend window.
+///
+/// Uses `OutputDamageTracker` for efficient re-rendering: only
+/// damaged regions are redrawn each frame.
+///
+/// Returns `true` if any damage was present and submitted.
+pub fn render_output_frame(
+    state: &mut WayRay,
+    backend: &mut WinitGraphicsBackend<GlesRenderer>,
+    damage_tracker: &mut OutputDamageTracker,
+) -> bool {
+    let output = state.output.clone();
+
+    // Get buffer age before bind (avoids borrow conflict).
+    let age = backend.buffer_age().unwrap_or(0);
+
+    // Render within a block so framebuffer is dropped before submit.
+    let render_damage = {
+        let (renderer, mut framebuffer) = match backend.bind() {
+            Ok(pair) => pair,
+            Err(err) => {
+                warn!(?err, "failed to bind winit backend for rendering");
+                return false;
+            }
+        };
+
+        // The empty custom elements slice needs a concrete type.
+        let custom_elements: &[TextureRenderElement<GlesTexture>] = &[];
+
+        let render_result = render_output::<_, _, Window, _>(
+            &output,
+            renderer,
+            &mut framebuffer,
+            1.0, // alpha
+            age,
+            [&state.space],
+            custom_elements,
+            damage_tracker,
+            CLEAR_COLOR,
+        );
+
+        match render_result {
+            Ok(result) => {
+                // Clone the damage rectangles so we can use them after
+                // the framebuffer is dropped.
+                Ok(result.damage.cloned())
+            }
+            Err(err) => {
+                warn!(?err, "damage tracker render failed");
+                Err(())
+            }
+        }
+    };
+    // framebuffer is now dropped, backend is no longer borrowed.
+
+    match render_damage {
+        Ok(damage) => {
+            let has_damage = damage.is_some();
+
+            let submit_result = if let Some(ref rects) = damage {
+                backend.submit(Some(rects))
+            } else {
+                backend.submit(None)
+            };
+
+            if let Err(err) = submit_result {
+                warn!(?err, "failed to submit frame");
+                return false;
+            }
+
+            // Send frame callbacks to all mapped surfaces so clients
+            // know they can draw the next frame.
+            let time = state.clock.now();
+            for window in state.space.elements() {
+                window.send_frame(&output, time, Some(std::time::Duration::ZERO), |_, _| {
+                    Some(output.clone())
+                });
+            }
+
+            has_damage
+        }
+        Err(()) => false,
+    }
+}