winit: initial minibrowser (#29976)

* winit: add minibrowser feature that depends on egui{,-winit}

* winit: carve out some space at the top of headed windows

* winit: minimal toolbar and egui/winit integration (but no painting)

* winit: try to paint with egui_glow (doesn’t work yet)

* winit: add comment about toolbar size

* Add framebuffer object, set it as glow's target

* compositing: clear only the viewport, not the whole framebuffer

* plumb the actual size of the egui toolbar to webrender

* fix formatting

* winit: fix crash when fbo is zero

* winit: don’t bother binding the framebuffer object

* winit: remove unsafe and get toolbar_height

* winit: location field should reflect the current top-level url

* [NFC] winit: move Minibrowser out of App::run

* winit: clean up toolbar height code

* winit: make App own the Minibrowser if any

* winit: make the go button work

* winit:make the location field reflect the current top-level url

* winit: allow enabling minibrowser from command line

* winit: tell compositor to repaint WR and flush when we repaint

* winit: fix bug where location field edits would get overridden

* winit: borrow the minibrowser once in App::handle_events

* winit: address todo about viewport origin coordinates

* winit: fix some minor problems with comments and errors

* winit: update location field once per HistoryChanged event

* winit: rename Window::set_toolbar_size to set_toolbar_height

* winit: take toolbar height into account in hit testing

* winit: pass egui only relevant CursorMoved events

* winit: scratch that, coalesce minibrowser updates instead

* ensure both minibrowser and WR are repainted on every frame

* compositing: only skip framebuffer clear in external present mode

* winit: destroy egui glow Painter when shutting down

* winit: clean up and fix license lint

* fix duplicate versions lint by downgrading bytemuck_derive

was egui_glow ^0.22.0 (0.22.0)
→ egui/bytemuck ^0.22.0 (0.22.0)
→ epaint/bytemuck ^0.22.0 (0.22.0)
→ bytemuck ^1.7.2 (1.13.1)
→ bytemuck_derive ^1.4 (1.4.1)
→ syn ^2.0.1 (2.0.28)

now lock has bytemuck_derive 1.4.0
→ syn ^1.0.99 (1.0.103)

* fix duplicate versions lint by disabling egui-winit/links

(we don’t need support for hyperlinks in our use of egui)

* squelch duplicate versions lint by excluding clipboard-win

* winit: fix compile warnings

* winit: make gleam an optional dependency under /minibrowser

* winit: remove cargo feature, since it’s not really optional

* winit: extract Minibrowser and related code to separate module

* winit: remove unnecessary trailing comma

* winit: simplify the ServoUrl serialisation optimisation

---------

Co-authored-by: atbrakhi <atbrakhi@igalia.com>

components/compositing/compositor.rs

@@ -230,6 +230,13 @@ pub struct IOCompositor<Window: WindowMethods + ?Sized> {
     /// taken before the render is complete will not reflect the
     /// most up to date rendering.
     waiting_on_pending_frame: bool,
+
+    /// Whether to send a ReadyToPresent message to the constellation after rendering a new frame,
+    /// allowing external code to draw to the framebuffer and decide when to present the frame.
+    external_present: bool,
+
+    /// Waiting for external code to call present.
+    waiting_on_present: bool,
 }
 
 #[derive(Clone, Copy)]
@@ -382,6 +389,8 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
             exit_after_load,
             convert_mouse_to_touch,
             waiting_on_pending_frame: false,
+            external_present: false,
+            waiting_on_present: false,
         }
     }
 
@@ -1525,6 +1534,12 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         target: CompositeTarget,
         rect: Option<Rect<f32, CSSPixel>>,
     ) -> Result<Option<Image>, UnableToComposite> {
+        if self.waiting_on_present {
+            return Err(UnableToComposite::NotReadyToPaintImage(
+                NotReadyToPaint::WaitingOnConstellation,
+            ));
+        }
+
         let size = self.embedder_coordinates.framebuffer.to_u32();
 
         if let Err(err) = self.webrender_surfman.make_gl_context_current() {
@@ -1703,8 +1718,15 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         };
 
         // Perform the page flip. This will likely block for a while.
-        if let Err(err) = self.webrender_surfman.present() {
-            warn!("Failed to present surface: {:?}", err);
+        if self.external_present {
+            self.waiting_on_present = true;
+            let msg =
+                ConstellationMsg::ReadyToPresent(self.root_pipeline.top_level_browsing_context_id);
+            if let Err(e) = self.constellation_chan.send(msg) {
+                warn!("Sending event to constellation failed ({:?}).", e);
+            }
+        } else {
+            self.present();
         }
 
         self.composition_request = CompositionRequest::NoCompositingNecessary;
@@ -1715,6 +1737,13 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         Ok(rv)
     }
 
+    pub fn present(&mut self) {
+        if let Err(err) = self.webrender_surfman.present() {
+            warn!("Failed to present surface: {:?}", err);
+        }
+        self.waiting_on_present = false;
+    }
+
     fn composite_if_necessary(&mut self, reason: CompositingReason) {
         if self.composition_request == CompositionRequest::NoCompositingNecessary {
             if self.is_running_problem_test {
@@ -1733,10 +1762,12 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         let gl = &self.webrender_gl;
         self.assert_gl_framebuffer_complete();
 
-        // Make framebuffer fully transparent.
-        gl.clear_color(0.0, 0.0, 0.0, 0.0);
-        gl.clear(gleam::gl::COLOR_BUFFER_BIT);
-        self.assert_gl_framebuffer_complete();
+        if !self.external_present {
+            // Make framebuffer fully transparent.
+            gl.clear_color(0.0, 0.0, 0.0, 0.0);
+            gl.clear(gleam::gl::COLOR_BUFFER_BIT);
+            self.assert_gl_framebuffer_complete();
+        }
 
         // Make the viewport white.
         let viewport = self.embedder_coordinates.get_flipped_viewport();
@@ -1919,6 +1950,10 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
             None => eprintln!("Unable to locate path to save captures"),
         }
     }
+
+    pub fn set_external_present(&mut self, value: bool) {
+        self.external_present = value;
+    }
 }
 
 /// Why we performed a composite. This is used for debugging.