[WIP] Implement damage tracking in iced_glutin

glutin/src/application.rs

@@ -2,6 +2,7 @@
 use crate::{mouse, Executor, Runtime, Size};
 use iced_graphics::window;
 use iced_graphics::Viewport;
+use iced_native::Damage;
 use iced_winit::application;
 use iced_winit::conversion;
 use iced_winit::{Clipboard, Debug, Proxy, Settings};
@@ -97,13 +98,18 @@ pub fn run<A, E, C>(
     );
     debug.startup_finished();
 
+    let mut damage = <<A as iced_native::program::Program>::Renderer
+        as iced_native::Renderer>::Output::default().damage(&state.primitive());
+
+    let mut first = true;
+
     event_loop.run(move |event, _, control_flow| match event {
         event::Event::MainEventsCleared => {
             if state.is_queue_empty() {
                 return;
             }
 
-            let command = runtime.enter(|| {
+            let (command, new_damage) = runtime.enter(|| {
                 state.update(
                     viewport.logical_size(),
                     conversion::cursor_position(
@@ -116,6 +122,17 @@ pub fn run<A, E, C>(
                 )
             });
 
+            eprintln!("{:?}", new_damage);
+            if !first {
+                damage = None;
+                if let Some(dmg) = new_damage {
+                    if dmg.len() > 0 {
+                        damage = Some(dmg);
+                    }
+                }
+            }
+            first = false;
+
             // If the application was updated
             if let Some(command) = command {
                 runtime.spawn(command);
@@ -187,39 +204,59 @@ pub fn run<A, E, C>(
             state.queue_message(message);
         }
         event::Event::RedrawRequested(_) => {
-            debug.render_started();
-
-            if resized {
+            if let Some(damage) = damage.take() {
+                debug.render_started();
                 let physical_size = viewport.physical_size();
 
-                context.resize(glutin::dpi::PhysicalSize::new(
-                    physical_size.width,
-                    physical_size.height,
-                ));
+                if resized {
+                    context.resize(glutin::dpi::PhysicalSize::new(
+                        physical_size.width,
+                        physical_size.height,
+                    ));
 
-                compositor.resize_viewport(physical_size);
+                    compositor.resize_viewport(physical_size);
 
-                resized = false;
-            }
+                    resized = false;
+                }
 
-            let new_mouse_interaction = compositor.draw(
-                &mut renderer,
-                &viewport,
-                background_color,
-                state.primitive(),
-                &debug.overlay(),
-            );
+                let new_mouse_interaction = compositor.draw(
+                    &mut renderer,
+                    &viewport,
+                    background_color,
+                    state.primitive(),
+                    &debug.overlay(),
+                );
 
-            context.swap_buffers().expect("Swap buffers");
+                if context.swap_buffers_with_damage_supported() {
+                    let scale = viewport.scale_factor() as f32;
+                    let rects = damage
+                        .iter()
+                        .map(|dmg| (*dmg * scale).snap())
+                        .map(|dmg| glutin::Rect {
+                            x: dmg.x,
+                            y: physical_size
+                                .height
+                                .saturating_sub(dmg.y + dmg.height),
+                            width: dmg.width.min(physical_size.width),
+                            height: dmg.height.min(physical_size.height),
+                        })
+                        .collect::<Vec<_>>();
+                    context
+                        .swap_buffers_with_damage(&rects[..])
+                        .expect("Swap buffers with damage");
+                } else {
+                    context.swap_buffers().expect("Swap buffers");
+                }
 
-            debug.render_finished();
+                debug.render_finished();
 
-            if new_mouse_interaction != mouse_interaction {
-                context.window().set_cursor_icon(
-                    conversion::mouse_interaction(new_mouse_interaction),
-                );
+                if new_mouse_interaction != mouse_interaction {
+                    context.window().set_cursor_icon(
+                        conversion::mouse_interaction(new_mouse_interaction),
+                    );
 
-                mouse_interaction = new_mouse_interaction;
+                    mouse_interaction = new_mouse_interaction;
+                }
             }
 
             // TODO: Handle animations!

native/src/program/state.rs

@@ -1,6 +1,6 @@
 use crate::{
-    Cache, Clipboard, Command, Debug, Event, Point, Program, Renderer, Size,
-    UserInterface,
+    Cache, Clipboard, Command, Damage, Debug, Event, Point, Program, Rectangle,
+    Renderer, Size, UserInterface,
 };
 
 /// The execution state of a [`Program`]. It leverages caching, event
@@ -100,7 +100,8 @@ where
     /// the widgets of the linked [`Program`] if necessary.
     ///
     /// Returns the [`Command`] obtained from [`Program`] after updating it,
-    /// only if an update was necessary.
+    /// only if an update was necessary; and a damage rectangle if any pixels
+    /// changed from the previous frame.
     ///
     /// [`Program`]: trait.Program.html
     pub fn update(
@@ -110,7 +111,7 @@ where
         clipboard: Option<&dyn Clipboard>,
         renderer: &mut P::Renderer,
         debug: &mut Debug,
-    ) -> Option<Command<P::Message>> {
+    ) -> (Option<Command<P::Message>>, Option<Vec<Rectangle>>) {
         let mut user_interface = build_user_interface(
             &mut self.program,
             self.cache.take().unwrap(),
@@ -133,12 +134,15 @@ where
 
         if messages.is_empty() {
             debug.draw_started();
-            self.primitive = user_interface.draw(renderer, cursor_position);
+            let primitive = user_interface.draw(renderer, cursor_position);
             debug.draw_finished();
 
             self.cache = Some(user_interface.into_cache());
 
-            None
+            let damage = self.primitive.damage(&primitive);
+            self.primitive = primitive;
+
+            (None, damage)
         } else {
             // When there are messages, we are forced to rebuild twice
             // for now :^)
@@ -164,12 +168,15 @@ where
             );
 
             debug.draw_started();
-            self.primitive = user_interface.draw(renderer, cursor_position);
+            let primitive = user_interface.draw(renderer, cursor_position);
             debug.draw_finished();
 
             self.cache = Some(user_interface.into_cache());
 
-            Some(commands)
+            let damage = self.primitive.damage(&primitive);
+            self.primitive = primitive;
+
+            (Some(commands), damage)
         }
     }
 }

native/src/renderer.rs

@@ -31,11 +31,11 @@ use crate::{layout, Element, Rectangle};
 /// updated between two frames.
 pub trait Damage {
     /// Calculates damage between two frames
-    fn damage(&self, other: &Self) -> Option<Rectangle>;
+    fn damage(&self, other: &Self) -> Option<Vec<Rectangle>>;
 }
 
 impl Damage for () {
-    fn damage(&self, _other: &Self) -> Option<Rectangle> {
+    fn damage(&self, _other: &Self) -> Option<Vec<Rectangle>> {
         None
     }
 }
@@ -44,7 +44,7 @@ impl<T, U> Damage for (T, U)
 where
     T: Damage,
 {
-    fn damage(&self, other: &Self) -> Option<Rectangle> {
+    fn damage(&self, other: &Self) -> Option<Vec<Rectangle>> {
         self.0.damage(&other.0)
     }
 }

winit/src/application.rs

@@ -184,7 +184,7 @@ pub fn run<A, E, C>(
                 return;
             }
 
-            let command = runtime.enter(|| {
+            let (command, _damage) = runtime.enter(|| {
                 state.update(
                     viewport.logical_size(),
                     conversion::cursor_position(