servo: Merge #16264 - Update WR (border fast paths, clip interfaces) …

…(from glennw:update-wr-borders-and-clips); r=Manishearth

Source-Repo: https://github.com/servo/servo
Source-Revision: 6a67688924b1b122be9c8ec456d6029dc02366a4

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 88b484524f996cce0d5c77dfd7e3634684cdb6da

servo/components/gfx/display_list/mod.rs

@@ -510,8 +510,8 @@ pub struct ScrollRoot {
     /// The position of this scroll root's frame in the parent stacking context.
     pub clip: Rect<Au>,
 
-    /// The size of the contents that can be scrolled inside of the scroll root.
-    pub size: Size2D<Au>,
+    /// The rect of the contents that can be scrolled inside of the scroll root.
+    pub content_rect: Rect<Au>,
 }
 
 impl ScrollRoot {

servo/components/layout/display_list_builder.rs

@@ -1963,24 +1963,29 @@ impl BlockFlowDisplayListBuilding for BlockFlow {
             &self.base.early_absolute_position_info.relative_containing_block_size,
             self.base.early_absolute_position_info.relative_containing_block_mode,
             coordinate_system);
-        let clip = self.fragment.stacking_relative_content_box(&border_box);
+        let content_box = self.fragment.stacking_relative_content_box(&border_box);
 
-        let has_scrolling_overflow = self.base.overflow.scroll.origin != Point2D::zero() ||
-                                     self.base.overflow.scroll.size.width > clip.size.width ||
-                                     self.base.overflow.scroll.size.height > clip.size.height;
-        self.mark_scrolling_overflow(has_scrolling_overflow);
-        if !has_scrolling_overflow {
+        // If we don't overflow our box at all, we can avoid creating a scroll root.
+        if self.base.overflow.scroll.origin == Point2D::zero() &&
+           self.base.overflow.scroll.size.width <= content_box.size.width &&
+           self.base.overflow.scroll.size.height <= content_box.size.height {
+            self.mark_scrolling_overflow(false);
             return containing_scroll_root_id;
         }
 
+        self.mark_scrolling_overflow(true);
+
         let new_scroll_root_id = ScrollRootId::new_of_type(self.fragment.node.id() as usize,
                                                            self.fragment.fragment_type());
+
+        let content_size = self.base.overflow.scroll.origin + self.base.overflow.scroll.size;
         state.add_scroll_root(
             ScrollRoot {
                 id: new_scroll_root_id,
                 parent_id: containing_scroll_root_id,
-                clip: clip,
-                size: self.base.overflow.scroll.size,
+                clip: Rect::new(Point2D::zero(), content_box.size),
+                content_rect: Rect::new(content_box.origin,
+                                        Size2D::new(content_size.x, content_size.y)),
             },
             self.base.stacking_context_id
         );

servo/components/layout/webrender_helpers.rs

@@ -414,6 +414,7 @@ impl WebRenderDisplayItemConverter for DisplayItem {
                                               stacking_context.bounds.to_rectf(),
                                               stacking_context.z_index,
                                               transform,
+                                              webrender_traits::TransformStyle::Flat,
                                               perspective,
                                               stacking_context.blend_mode.to_blend_mode(),
                                               stacking_context.filters.to_filter_ops());
@@ -425,8 +426,8 @@ impl WebRenderDisplayItemConverter for DisplayItem {
                                                    None);
 
                 let provided_id = ScrollLayerId::new(item.scroll_root.id.0 as u64, builder.pipeline_id);
-                let id = builder.define_clip(clip,
-                                             item.scroll_root.size.to_sizef(),
+                let id = builder.define_clip(item.scroll_root.content_rect.to_rectf(),
+                                             clip,
                                              Some(provided_id));
                 debug_assert!(provided_id == id);
             }