layout: Make the compositor rather than layout determine the position of

each iframe.

The old code that attempted to do this during layout wasn't able to work
for multiple reasons: it couldn't know where the iframe was going to be
on the page (because of nested iframes), and at the time it was building
the display list for a fragment it couldn't know where that fragment was
going to be in page coordinates.

This patch rewrites that code so that both the sizes and positions of
iframes are determined by the compositor. Layout layerizes all iframes
and marks the iframe layers with the appropriate pipeline and subpage
IDs so that the compositor can place them correctly. This approach is
similar in spirit to Gecko's `RefLayer` infrastructure. The logic that
determines when it is time to take the screenshot for reftests has been
significantly revamped to deal with this change in delegation of
responsibility.

Additionally, this code removes the infrastructure that sends layout
data back to the layout task to be destroyed, since it is now all
thread-safe and can be destroyed on the script task.

The failing tests now fail because of a pre-existing bug related to
intrinsic heights and borders on inline replaced elements. They happened
to pass before because we never rendered the iframes at all, which meant
they never had a chance to draw the red border the tests expect to not
render!

Closes #7377.

components/compositing/constellation.rs

@@ -16,14 +16,12 @@ use clipboard::ClipboardContext;
 use compositor_task::CompositorProxy;
 use compositor_task::Msg as CompositorMsg;
 use devtools_traits::{ChromeToDevtoolsControlMsg, DevtoolsControlMsg};
-use euclid::point::Point2D;
-use euclid::rect::{Rect, TypedRect};
 use euclid::scale_factor::ScaleFactor;
-use euclid::size::Size2D;
+use euclid::size::{Size2D, TypedSize2D};
 use gfx::font_cache_task::FontCacheTask;
 use ipc_channel::ipc::{self, IpcSender};
 use layout_traits::{LayoutControlChan, LayoutTaskFactory};
-use msg::compositor_msg::{Epoch, LayerId};
+use msg::compositor_msg::Epoch;
 use msg::constellation_msg::AnimationState;
 use msg::constellation_msg::Msg as ConstellationMsg;
 use msg::constellation_msg::WebDriverCommandMsg;
@@ -136,6 +134,10 @@ pub struct Constellation<LTF, STF> {
 
     /// A list of in-process senders to `WebGLPaintTask`s.
     webgl_paint_tasks: Vec<Sender<CanvasMsg>>,
+
+    /// A list of senders that are waiting to be notified whenever a pipeline or subpage ID comes
+    /// in.
+    subpage_id_senders: HashMap<(PipelineId, SubpageId), Vec<IpcSender<PipelineId>>>,
 }
 
 /// State needed to construct a constellation.
@@ -217,7 +219,7 @@ impl<'a> Iterator for FrameTreeIterator<'a> {
 
 pub struct SendableFrameTree {
     pub pipeline: CompositionPipeline,
-    pub rect: Option<TypedRect<PagePx, f32>>,
+    pub size: Option<TypedSize2D<PagePx, f32>>,
     pub children: Vec<SendableFrameTree>,
 }
 
@@ -280,6 +282,7 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                 webdriver: WebDriverData::new(),
                 canvas_paint_tasks: Vec::new(),
                 webgl_paint_tasks: Vec::new(),
+                subpage_id_senders: HashMap::new(),
             };
             constellation.run();
         });
@@ -298,7 +301,7 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
     /// Helper function for creating a pipeline
     fn new_pipeline(&mut self,
                     parent_info: Option<(PipelineId, SubpageId)>,
-                    initial_window_rect: Option<TypedRect<PagePx, f32>>,
+                    initial_window_size: Option<TypedSize2D<PagePx, f32>>,
                     script_channel: Option<Sender<ConstellationControlMsg>>,
                     load_data: LoadData)
                     -> PipelineId {
@@ -320,7 +323,7 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                 storage_task: self.storage_task.clone(),
                 time_profiler_chan: self.time_profiler_chan.clone(),
                 mem_profiler_chan: self.mem_profiler_chan.clone(),
-                window_rect: initial_window_rect,
+                window_size: initial_window_size,
                 script_chan: script_channel,
                 load_data: load_data,
                 device_pixel_ratio: self.window_size.device_pixel_ratio,
@@ -396,11 +399,11 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                 debug!("constellation got init load URL message");
                 self.handle_init_load(url);
             }
-            // A layout assigned a size and position to a subframe. This needs to be reflected by
-            // all frame trees in the navigation context containing the subframe.
-            ConstellationMsg::FrameRect(pipeline_id, subpage_id, rect) => {
-                debug!("constellation got frame rect message");
-                self.handle_frame_rect_msg(pipeline_id, subpage_id, Rect::from_untyped(&rect));
+            // The compositor discovered the size of a subframe. This needs to be reflected by all
+            // frame trees in the navigation context containing the subframe.
+            ConstellationMsg::FrameSize(pipeline_id, subpage_id, size) => {
+                debug!("constellation got frame size message");
+                self.handle_frame_size_msg(pipeline_id, subpage_id, &Size2D::from_untyped(&size));
             }
             ConstellationMsg::ScriptLoadedURLInIFrame(url,
                                                       source_pipeline_id,
@@ -417,7 +420,9 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                                                             old_subpage_id,
                                                             sandbox);
             }
-            ConstellationMsg::SetCursor(cursor) => self.handle_set_cursor_msg(cursor),
+            ConstellationMsg::SetCursor(cursor) => {
+                self.handle_set_cursor_msg(cursor)
+            }
             ConstellationMsg::ChangeRunningAnimationsState(pipeline_id, animation_state) => {
                 self.handle_change_running_animations_state(pipeline_id, animation_state)
             }
@@ -537,6 +542,12 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                 debug!("constellation got NodeStatus message");
                 self.compositor_proxy.send(CompositorMsg::Status(message));
             }
+            ConstellationMsg::PrepareForSubpageLayerCreation(pipeline_id, subpage_id) => {
+                self.compositor_proxy.send(CompositorMsg::CreateLayerForSubpage(
+                        pipeline_id,
+                        subpage_id,
+                        self.subpage_map.get(&(pipeline_id, subpage_id)).map(|x| *x)))
+            }
         }
         true
     }
@@ -585,10 +596,10 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
         }
         debug!("creating replacement pipeline for about:failure");
 
-        let window_rect = self.pipeline(pipeline_id).rect;
+        let window_size = self.pipeline(pipeline_id).size;
         let new_pipeline_id =
             self.new_pipeline(parent_info,
-                              window_rect,
+                              window_size,
                               None,
                               LoadData::new(Url::parse("about:failure").unwrap()));
 
@@ -596,44 +607,39 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
     }
 
     fn handle_init_load(&mut self, url: Url) {
-        let window_rect = Rect::new(Point2D::zero(), self.window_size.visible_viewport);
+        let window_size = self.window_size.visible_viewport;
         let root_pipeline_id =
-            self.new_pipeline(None, Some(window_rect), None, LoadData::new(url.clone()));
+            self.new_pipeline(None, Some(window_size), None, LoadData::new(url.clone()));
         self.handle_load_start_msg(&root_pipeline_id);
         self.push_pending_frame(root_pipeline_id, None);
         self.compositor_proxy.send(CompositorMsg::ChangePageUrl(root_pipeline_id, url));
     }
 
-    fn handle_frame_rect_msg(&mut self, containing_pipeline_id: PipelineId, subpage_id: SubpageId,
-                             rect: TypedRect<PagePx, f32>) {
+    fn handle_frame_size_msg(&mut self,
+                             containing_pipeline_id: PipelineId,
+                             subpage_id: SubpageId,
+                             size: &TypedSize2D<PagePx, f32>) {
         // Store the new rect inside the pipeline
         let (pipeline_id, script_chan) = {
             // Find the pipeline that corresponds to this rectangle. It's possible that this
             // pipeline may have already exited before we process this message, so just
             // early exit if that occurs.
-            let pipeline_id = self.subpage_map.get(&(containing_pipeline_id, subpage_id)).map(|id| *id);
+            let pipeline_id = self.subpage_map
+                                  .get(&(containing_pipeline_id, subpage_id))
+                                  .map(|id| *id);
             let pipeline = match pipeline_id {
                 Some(pipeline_id) => self.mut_pipeline(pipeline_id),
                 None => return,
             };
-            pipeline.rect = Some(rect);
+            pipeline.size = Some(*size);
             (pipeline.id, pipeline.script_chan.clone())
         };
 
         script_chan.send(ConstellationControlMsg::Resize(pipeline_id, WindowSizeData {
-            visible_viewport: rect.size,
-            initial_viewport: rect.size * ScaleFactor::new(1.0),
+            visible_viewport: *size,
+            initial_viewport: *size * ScaleFactor::new(1.0),
             device_pixel_ratio: self.window_size.device_pixel_ratio,
         })).unwrap();
-
-        // If this pipeline is in the current frame tree,
-        // send the updated rect to the script and compositor tasks
-        if self.pipeline_is_in_current_frame(pipeline_id) {
-            self.compositor_proxy.send(CompositorMsg::SetLayerRect(
-                pipeline_id,
-                LayerId::null(),
-                rect.to_untyped()));
-        }
     }
 
     // The script task associated with pipeline_id has loaded a URL in an iframe via script. This
@@ -674,14 +680,24 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
         let old_pipeline_id = old_subpage_id.map(|old_subpage_id| {
             self.find_subpage(containing_pipeline_id, old_subpage_id).id
         });
-        let window_rect = old_pipeline_id.and_then(|old_pipeline_id| {
-            self.pipeline(old_pipeline_id).rect
+        let window_size = old_pipeline_id.and_then(|old_pipeline_id| {
+            self.pipeline(old_pipeline_id).size
         });
         let new_pipeline_id = self.new_pipeline(Some((containing_pipeline_id, new_subpage_id)),
-                                                window_rect,
+                                                window_size,
                                                 script_chan,
                                                 LoadData::new(url));
+
         self.subpage_map.insert((containing_pipeline_id, new_subpage_id), new_pipeline_id);
+
+        // If anyone is waiting to know the pipeline ID, send that information now.
+        if let Some(subpage_id_senders) = self.subpage_id_senders.remove(&(containing_pipeline_id,
+                                                                           new_subpage_id)) {
+            for subpage_id_sender in subpage_id_senders.into_iter() {
+                subpage_id_sender.send(new_pipeline_id).unwrap();
+            }
+        }
+
         self.push_pending_frame(new_pipeline_id, old_pipeline_id);
     }
 
@@ -739,8 +755,8 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                 // changes would be overridden by changing the subframe associated with source_id.
 
                 // Create the new pipeline
-                let window_rect = self.pipeline(source_id).rect;
-                let new_pipeline_id = self.new_pipeline(None, window_rect, None, load_data);
+                let window_size = self.pipeline(source_id).size;
+                let new_pipeline_id = self.new_pipeline(None, window_size, None, load_data);
                 self.push_pending_frame(new_pipeline_id, Some(source_id));
 
                 // Send message to ScriptTask that will suspend all timers
@@ -954,7 +970,9 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
         self.focus_parent_pipeline(pipeline_id);
     }
 
-    fn handle_remove_iframe_msg(&mut self, containing_pipeline_id: PipelineId, subpage_id: SubpageId) {
+    fn handle_remove_iframe_msg(&mut self,
+                                containing_pipeline_id: PipelineId,
+                                subpage_id: SubpageId) {
         let pipeline_id = self.find_subpage(containing_pipeline_id, subpage_id).id;
         let frame_id = self.pipeline_to_frame_map.get(&pipeline_id).map(|id| *id);
         match frame_id {
@@ -1172,7 +1190,8 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
         for pending_frame in &self.pending_frames {
             let pipeline = self.pipelines.get(&pending_frame.new_pipeline_id).unwrap();
             if pipeline.parent_info.is_none() {
-                let _ = pipeline.script_chan.send(ConstellationControlMsg::Resize(pipeline.id, new_size));
+                let _ = pipeline.script_chan.send(ConstellationControlMsg::Resize(pipeline.id,
+                                                                                  new_size));
             }
         }
 
@@ -1180,7 +1199,9 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
     }
 
     /// Handle updating actual viewport / zoom due to @viewport rules
-    fn handle_viewport_constrained_msg(&mut self, pipeline_id: PipelineId, constraints: ViewportConstraints) {
+    fn handle_viewport_constrained_msg(&mut self,
+                                       pipeline_id: PipelineId,
+                                       constraints: ViewportConstraints) {
         self.compositor_proxy.send(CompositorMsg::ViewportConstrained(pipeline_id, constraints));
     }
 
@@ -1196,12 +1217,6 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
             return false;
         }
 
-        // If there are pending changes to the current frame
-        // tree, the image is not stable yet.
-        if self.pending_frames.len() > 0 {
-            return false;
-        }
-
         // Step through the current frame tree, checking that the script
         // task is idle, and that the current epoch of the layout task
         // matches what the compositor has painted. If all these conditions
@@ -1215,12 +1230,11 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
             let (sender, receiver) = channel();
             let msg = ConstellationControlMsg::GetCurrentState(sender, frame.current);
             pipeline.script_chan.send(msg).unwrap();
-            if receiver.recv().unwrap() == ScriptState::DocumentLoading {
+            let result = receiver.recv().unwrap();
+            if result == ScriptState::DocumentLoading {
                 return false;
             }
 
-            // Synchronously query the layout task for this pipeline
-            // to see if it is idle.
             let (sender, receiver) = ipc::channel().unwrap();
             let msg = LayoutControlMsg::GetWebFontLoadState(sender);
             pipeline.layout_chan.0.send(msg).unwrap();
@@ -1228,43 +1242,39 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                 return false;
             }
 
-            // Check the visible rectangle for this pipeline. If the constellation
-            // hasn't received a rectangle for this pipeline yet, then assume
-            // that the output image isn't stable yet.
-            match pipeline.rect {
-                Some(rect) => {
-                    // If the rectangle for this pipeline is zero sized, it will
-                    // never be painted. In this case, don't query the layout
-                    // task as it won't contribute to the final output image.
-                    if rect.size == Size2D::zero() {
-                        continue;
-                    }
+            // Check the visible rectangle for this pipeline. If the constellation has received a
+            // size for the pipeline, then its painting should be up to date. If the constellation
+            // *hasn't* received a size, it could be that the layer was hidden by script before the
+            // compositor discovered it, so we just don't check the layer.
+            if let Some(size) = pipeline.size {
+                // If the rectangle for this pipeline is zero sized, it will
+                // never be painted. In this case, don't query the layout
+                // task as it won't contribute to the final output image.
+                if size == Size2D::zero() {
+                    continue;
+                }
 
-                    // Get the epoch that the compositor has drawn for this pipeline.
-                    let compositor_epoch = pipeline_states.get(&frame.current);
-                    match compositor_epoch {
-                        Some(compositor_epoch) => {
-                            // Synchronously query the layout task to see if the current
-                            // epoch matches what the compositor has drawn. If they match
-                            // (and script is idle) then this pipeline won't change again
-                            // and can be considered stable.
-                            let (sender, receiver) = ipc::channel().unwrap();
-                            let LayoutControlChan(ref layout_chan) = pipeline.layout_chan;
-                            layout_chan.send(LayoutControlMsg::GetCurrentEpoch(sender)).unwrap();
-                            let layout_task_epoch = receiver.recv().unwrap();
-                            if layout_task_epoch != *compositor_epoch {
-                                return false;
-                            }
-                        }
-                        None => {
-                            // The compositor doesn't know about this pipeline yet.
-                            // Assume it hasn't rendered yet.
+                // Get the epoch that the compositor has drawn for this pipeline.
+                let compositor_epoch = pipeline_states.get(&frame.current);
+                match compositor_epoch {
+                    Some(compositor_epoch) => {
+                        // Synchronously query the layout task to see if the current
+                        // epoch matches what the compositor has drawn. If they match
+                        // (and script is idle) then this pipeline won't change again
+                        // and can be considered stable.
+                        let (sender, receiver) = ipc::channel().unwrap();
+                        let LayoutControlChan(ref layout_chan) = pipeline.layout_chan;
+                        layout_chan.send(LayoutControlMsg::GetCurrentEpoch(sender)).unwrap();
+                        let layout_task_epoch = receiver.recv().unwrap();
+                        if layout_task_epoch != *compositor_epoch {
                             return false;
                         }
                     }
-                }
-                None => {
-                    return false;
+                    None => {
+                        // The compositor doesn't know about this pipeline yet.
+                        // Assume it hasn't rendered yet.
+                        return false;
+                    }
                 }
             }
         }
@@ -1354,7 +1364,7 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
 
         let mut frame_tree = SendableFrameTree {
             pipeline: pipeline.to_sendable(),
-            rect: pipeline.rect,
+            size: pipeline.size,
             children: vec!(),
         };
 
@@ -1409,7 +1419,8 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
             // If this is an iframe, then send the event with new url
             if let Some((containing_pipeline_id, subpage_id, url)) = event_info {
                 let parent_pipeline = self.pipeline(containing_pipeline_id);
-                parent_pipeline.trigger_mozbrowser_event(subpage_id, MozBrowserEvent::LocationChange(url));
+                parent_pipeline.trigger_mozbrowser_event(subpage_id,
+                                                         MozBrowserEvent::LocationChange(url));
             }
         }
     }
@@ -1451,7 +1462,8 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
         self.pipelines.get_mut(&pipeline_id).expect("unable to find pipeline - this is a bug")
     }
 
-    fn find_subpage(&mut self, containing_pipeline_id: PipelineId, subpage_id: SubpageId) -> &mut Pipeline {
+    fn find_subpage(&mut self, containing_pipeline_id: PipelineId, subpage_id: SubpageId)
+                    -> &mut Pipeline {
         let pipeline_id = *self.subpage_map
                                .get(&(containing_pipeline_id, subpage_id))
                                .expect("no subpage pipeline_id");