From 39600f9f4e1415d27df5a03530fd637c1b10f16f Mon Sep 17 00:00:00 2001
From: Martin Robinson <mrobinson@igalia.com>
Date: Tue, 4 Apr 2017 19:00:26 +0200
Subject: [PATCH] Update to support new clipping coordinates change

---
 components/gfx/display_list/mod.rs        |  4 ++--
 components/layout/display_list_builder.rs | 21 +++++++++++++--------
 components/layout/webrender_helpers.rs    |  4 ++--
 3 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/components/gfx/display_list/mod.rs b/components/gfx/display_list/mod.rs
index ee3494e1b95..e43767ddadd 100644
--- a/components/gfx/display_list/mod.rs
+++ b/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 {
diff --git a/components/layout/display_list_builder.rs b/components/layout/display_list_builder.rs
index 94e388dff72..8c390487f5c 100644
--- a/components/layout/display_list_builder.rs
+++ b/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
         );
diff --git a/components/layout/webrender_helpers.rs b/components/layout/webrender_helpers.rs
index 8f1f76f413f..355c5ebb7fc 100644
--- a/components/layout/webrender_helpers.rs
+++ b/components/layout/webrender_helpers.rs
@@ -425,8 +425,8 @@ 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);
             }