2020: add and call Fragment::build_display_list

components/layout_2020/flow/root.rs

@@ -6,7 +6,7 @@ use crate::dom_traversal::{Contents, NodeExt};
 use crate::flow::construct::ContainsFloats;
 use crate::flow::float::FloatBox;
 use crate::flow::{BlockContainer, BlockFormattingContext, BlockLevelBox};
-use crate::fragments::Fragment;
+use crate::fragments::{Fragment, IsContentful};
 use crate::geom;
 use crate::geom::flow_relative::Vec2;
 use crate::positioned::AbsolutelyPositionedBox;
@@ -21,6 +21,7 @@ use style::context::SharedStyleContext;
 use style::properties::ComputedValues;
 use style::values::computed::{Length, LengthOrAuto};
 use style_traits::CSSPixel;
+use webrender_api::DisplayListBuilder;
 
 pub struct BoxTreeRoot(BlockFormattingContext);
 pub struct FragmentTreeRoot(Vec<Fragment>);
@@ -129,3 +130,13 @@ impl BoxTreeRoot {
         FragmentTreeRoot(flow_children.fragments)
     }
 }
+
+impl FragmentTreeRoot {
+    pub fn build_display_list(&self, builder: &mut DisplayListBuilder) -> IsContentful {
+        let mut is_contentful = IsContentful(false);
+        for fragment in &self.0 {
+            fragment.build_display_list(builder, &mut is_contentful)
+        }
+        is_contentful
+    }
+}

components/layout_2020/fragments.rs

@@ -9,6 +9,7 @@ use servo_arc::Arc;
 use style::properties::ComputedValues;
 use style::values::computed::Length;
 use style::Zero;
+use webrender_api::DisplayListBuilder;
 
 pub(crate) enum Fragment {
     Box(BoxFragment),
@@ -123,3 +124,18 @@ impl CollapsedMargin {
         self.max_positive + self.min_negative
     }
 }
+
+/// Contentful paint, for the purpose of
+/// https://w3c.github.io/paint-timing/#first-contentful-paint
+/// (i.e. the display list contains items of type text,
+/// image, non-white canvas or SVG). Used by metrics.
+pub struct IsContentful(pub bool);
+
+impl Fragment {
+    pub(crate) fn build_display_list(
+        &self,
+        builder: &mut DisplayListBuilder,
+        is_contentful: &mut IsContentful,
+    ) {
+    }
+}

components/layout_thread_2020/lib.rs

@@ -1108,7 +1108,9 @@ impl LayoutThread {
         }
 
         // Perform post-style recalculation layout passes.
-        self.perform_post_style_recalc_layout_passes(&data.reflow_goal, Some(&document));
+        if let Some(root) = &*self.fragment_tree_root.borrow() {
+            self.perform_post_style_recalc_layout_passes(root, &data.reflow_goal, Some(&document));
+        }
 
         self.first_reflow.set(false);
         self.respond_to_query_if_necessary(&data.reflow_goal, &mut *rw_data, &mut layout_context);
@@ -1230,7 +1232,10 @@ impl LayoutThread {
             );
         }
 
-        if let Some(author_shared_lock) = self.document_shared_lock.clone() {
+        if let Some(root) = &*self.fragment_tree_root.borrow() {
+            // Unwrap here should not panic since self.fragment_tree_root is only ever set to Some(_)
+            // in handle_reflow() where self.document_shared_lock is as well.
+            let author_shared_lock = self.document_shared_lock.clone().unwrap();
             let author_guard = author_shared_lock.read();
             let ua_or_user_guard = UA_STYLESHEETS.shared_lock.read();
             let _guards = StylesheetGuards {
@@ -1238,12 +1243,13 @@ impl LayoutThread {
                 ua_or_user: &ua_or_user_guard,
             };
 
-            self.perform_post_style_recalc_layout_passes(&ReflowGoal::TickAnimations, None);
+            self.perform_post_style_recalc_layout_passes(root, &ReflowGoal::TickAnimations, None);
         }
     }
 
     fn perform_post_style_recalc_layout_passes(
         &self,
+        fragment_tree: &layout::FragmentTreeRoot,
         reflow_goal: &ReflowGoal,
         document: Option<&ServoLayoutDocument>,
     ) {
@@ -1261,16 +1267,13 @@ impl LayoutThread {
             document.will_paint();
         }
 
-        let viewport_size = Size2D::new(
+        let viewport_size = webrender_api::units::LayoutSize::from_untyped(Size2D::new(
             self.viewport_size.width.to_f32_px(),
             self.viewport_size.height.to_f32_px(),
-        );
-
-        let viewport_size = webrender_api::units::LayoutSize::from_untyped(viewport_size);
-
-        let display_list =
+        ));
+        let mut display_list =
             webrender_api::DisplayListBuilder::new(self.id.to_webrender(), viewport_size);
-        let is_contentful = false;
+        let is_contentful = fragment_tree.build_display_list(&mut display_list);
 
         debug!("Layout done!");
 
@@ -1282,7 +1285,7 @@ impl LayoutThread {
         // sending the display list to WebRender in order to set time related
         // Progressive Web Metrics.
         self.paint_time_metrics
-            .maybe_observe_paint_time(self, epoch, is_contentful);
+            .maybe_observe_paint_time(self, epoch, is_contentful.0);
 
         let mut txn = webrender_api::Transaction::new();
         txn.set_display_list(