Fix servoshell can't respond when there's no minibrowser (#30598)

* Fix servoshell can't respond when there's no minibrowser

* Remove external_field and update documentation

* Update documentation

* Fix crash when handling ReadyToPresent if it's headless mode

* Fix some wpt tests got timedout

components/compositing/compositor.rs

@@ -240,10 +240,6 @@ pub struct IOCompositor<Window: WindowMethods + ?Sized> {
     /// 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,
 }
@@ -410,7 +406,6 @@ 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,
         }
     }
@@ -1858,8 +1853,8 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
             _ => None,
         };
 
-        // Perform the page flip. This will likely block for a while.
+        // Nottify embedder that servo is ready to present.
-        if self.external_present {
+        // Embedder should call `present` to tell compositor to continue rendering.
         self.waiting_on_present = true;
         let msg = ConstellationMsg::ReadyToPresent(
             self.root_content_pipeline.top_level_browsing_context_id,
@@ -1867,9 +1862,6 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         if let Err(e) = self.constellation_chan.send(msg) {
             warn!("Sending event to constellation failed ({:?}).", e);
         }
-        } else {
-            self.present();
-        }
 
         self.composition_request = CompositionRequest::NoCompositingNecessary;
 
@@ -1904,13 +1896,6 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         let gl = &self.webrender_gl;
         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();
-        }
-
         // Set the viewport background based on prefs.
         let viewport = self.embedder_coordinates.get_flipped_viewport();
         gl.scissor(
@@ -2109,8 +2094,4 @@ 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;
-    }
 }

components/servo/lib.rs

@@ -761,10 +761,6 @@ where
         self.compositor.deinit();
     }
 
-    pub fn set_external_present(&mut self, value: bool) {
-        self.compositor.set_external_present(value)
-    }
-
     pub fn present(&mut self) {
         self.compositor.present();
     }

ports/servoshell/app.rs

@@ -41,8 +41,15 @@ pub struct App {
 
 /// Action to be taken by the caller of [`App::handle_events`].
 enum PumpResult {
+    /// The caller should shut down Servo and its related context.
     Shutdown,
+    /// A new frame is ready to present. The caller can paint other things themselves during this
+    /// period, but has to call [`Servo::present`] to perform page flip and tell Servo compositor
+    /// to continue rendering.
     ReadyToPresent,
+    /// The size has changed. The caller can paint other things themselves during this
+    /// period, but has to call [`Servo::present`] to perform page flip and tell Servo compositor
+    /// to continue rendering.
     Resize,
 }
 
@@ -117,10 +124,6 @@ impl App {
         // frame, set this to false, so we can avoid an unnecessary recomposite.
         let mut need_recomposite = true;
 
-        // If we have a minibrowser, ask the compositor to notify us when a new frame
-        // is ready to present, so that we can paint the minibrowser then present.
-        let external_present = app.minibrowser.is_some();
-
         let t_start = Instant::now();
         let mut t = t_start;
         let ev_waker = events_loop.create_event_loop_waker();
@@ -175,7 +178,6 @@ impl App {
 
                     let servo_data = Servo::new(embedder, window.clone(), user_agent.clone());
                     let mut servo = servo_data.servo;
-                    servo.set_external_present(external_present);
 
                     servo.handle_events(vec![EmbedderEvent::NewBrowser(
                         initial_url.to_owned(),
@@ -209,9 +211,7 @@ impl App {
                     minibrowser.update(window.winit_window().unwrap(), "RedrawRequested");
                     minibrowser.paint(window.winit_window().unwrap());
                 }
-                if external_present {
                 app.servo.as_mut().unwrap().present();
-                }
 
                 // By default, the next RedrawRequested event will need to recomposite.
                 need_recomposite = true;
@@ -296,7 +296,12 @@ impl App {
                     trace!("PumpResult::ReadyToPresent");
 
                     // Request a winit redraw event, so we can paint the minibrowser and present.
-                    window.winit_window().unwrap().request_redraw();
+                    // Otherwise, it's in headless mode and we present directly.
+                    if let Some(window) = window.winit_window() {
+                        window.request_redraw();
+                    } else {
+                        app.servo.as_mut().unwrap().present();
+                    }
 
                     // We don’t need the compositor to paint to this frame during the redraw event.
                     // TODO(servo#30331) broken on macOS?
@@ -314,9 +319,7 @@ impl App {
                         minibrowser.update(window.winit_window().unwrap(), "PumpResult::Resize");
                         minibrowser.paint(window.winit_window().unwrap());
                     }
-                    if external_present {
                     app.servo.as_mut().unwrap().present();
-                    }
                 },
                 None => {},
             }