layout: Separate out overflow-for-scrolling from overflow-for-paint.

Closes #9484.

components/layout/block.rs

@@ -43,7 +43,7 @@ use flow::{NEEDS_LAYER, PostorderFlowTraversal, PreorderFlowTraversal, Fragmenta
 use flow::{self, BaseFlow, EarlyAbsolutePositionInfo, Flow, FlowClass, ForceNonfloatedFlag};
 use flow_list::FlowList;
 use flow_ref::FlowRef;
-use fragment::{CoordinateSystem, Fragment, FragmentBorderBoxIterator, HAS_LAYER};
+use fragment::{CoordinateSystem, Fragment, FragmentBorderBoxIterator, HAS_LAYER, Overflow};
 use fragment::{SpecificFragmentInfo};
 use gfx::display_list::{ClippingRegion, DisplayList};
 use gfx_traits::LayerId;
@@ -2098,7 +2098,7 @@ impl Flow for BlockFlow {
         self.fragment.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         let flow_size = self.base.position.size.to_physical(self.base.writing_mode);
         self.fragment.compute_overflow(&flow_size,
                                        &self.base

components/layout/display_list_builder.rs

@@ -1218,7 +1218,7 @@ impl FragmentDisplayListBuilding for Fragment {
                                                   CoordinateSystem::Parent)
             }
             StackingContextCreationMode::InnerScrollWrapper => {
-                Rect::new(Point2D::zero(), base_flow.overflow.size)
+                Rect::new(Point2D::zero(), base_flow.overflow.scroll.size)
             }
         };
         let overflow = match mode {
@@ -1228,7 +1228,7 @@ impl FragmentDisplayListBuilding for Fragment {
                 let border_box_offset =
                     border_box.translate(&-base_flow.stacking_relative_position).origin;
                 // Then, using that, compute our overflow region relative to our border box.
-                base_flow.overflow.translate(&-border_box_offset)
+                base_flow.overflow.paint.translate(&-border_box_offset)
             }
             StackingContextCreationMode::InnerScrollWrapper |
             StackingContextCreationMode::OuterScrollWrapper => {

components/layout/flex.rs

@@ -10,7 +10,7 @@ use app_units::Au;
 use block::BlockFlow;
 use context::LayoutContext;
 use display_list_builder::FlexFlowDisplayListBuilding;
-use euclid::{Point2D, Rect};
+use euclid::Point2D;
 use floats::FloatKind;
 use flow;
 use flow::INLINE_POSITION_IS_STATIC;
@@ -18,7 +18,7 @@ use flow::IS_ABSOLUTELY_POSITIONED;
 use flow::ImmutableFlowUtils;
 use flow::{Flow, FlowClass, OpaqueFlow};
 use flow::{HAS_LEFT_FLOATED_DESCENDANTS, HAS_RIGHT_FLOATED_DESCENDANTS};
-use fragment::{Fragment, FragmentBorderBoxIterator};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow};
 use gfx::display_list::DisplayList;
 use incremental::{REFLOW, REFLOW_OUT_OF_FLOW};
 use layout_debug;
@@ -432,7 +432,7 @@ impl Flow for FlexFlow {
         self.block_flow.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         self.block_flow.compute_overflow()
     }
 

components/layout/flow.rs

@@ -32,7 +32,7 @@ use euclid::{Point2D, Rect, Size2D};
 use floats::Floats;
 use flow_list::{FlowList, FlowListIterator, MutFlowListIterator};
 use flow_ref::{self, FlowRef, WeakFlowRef};
-use fragment::{Fragment, FragmentBorderBoxIterator, SpecificFragmentInfo};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow, SpecificFragmentInfo};
 use gfx::display_list::{ClippingRegion, DisplayList};
 use gfx_traits::{LayerId, LayerType};
 use incremental::{RECONSTRUCT_FLOW, REFLOW, REFLOW_OUT_OF_FLOW, REPAINT, RestyleDamage};
@@ -266,15 +266,16 @@ pub trait Flow: fmt::Debug + Sync + Send + 'static {
                 // FIXME(#2795): Get the real container size.
                 let container_size = Size2D::zero();
                 for kid in mut_base(self).children.iter_mut() {
-                    let kid_overflow = base(kid).overflow;
+                    let mut kid_overflow = base(kid).overflow;
                     let kid_position = base(kid).position.to_physical(base(kid).writing_mode,
                                                                       container_size);
-                    overflow = overflow.union(&kid_overflow.translate(&kid_position.origin))
+                    kid_overflow.translate(&kid_position.origin);
+                    overflow.union(&kid_overflow)
                 }
             }
             _ => {}
         }
-        mut_base(self).overflow = overflow;
+        mut_base(self).overflow = overflow
     }
 
     /// Phase 4 of reflow: computes absolute positions.
@@ -286,7 +287,7 @@ pub trait Flow: fmt::Debug + Sync + Send + 'static {
     fn build_display_list(&mut self, layout_context: &LayoutContext);
 
     /// Returns the union of all overflow rects of all of this flow's fragments.
-    fn compute_overflow(&self) -> Rect<Au>;
+    fn compute_overflow(&self) -> Overflow;
 
     /// Iterates through border boxes of all of this flow's fragments.
     /// Level provides a zero based index indicating the current
@@ -865,7 +866,7 @@ pub struct BaseFlow {
 
     /// The amount of overflow of this flow, relative to the containing block. Must include all the
     /// pixels of all the display list items for correct invalidation.
-    pub overflow: Rect<Au>,
+    pub overflow: Overflow,
 
     /// Data used during parallel traversals.
     ///
@@ -1078,7 +1079,7 @@ impl BaseFlow {
             children: FlowList::new(),
             intrinsic_inline_sizes: IntrinsicISizes::new(),
             position: LogicalRect::zero(writing_mode),
-            overflow: Rect::zero(),
+            overflow: Overflow::new(),
             parallel: FlowParallelInfo::new(),
             floats: Floats::new(writing_mode),
             collapsible_margins: CollapsibleMargins::new(),
@@ -1132,7 +1133,7 @@ impl BaseFlow {
         let container_size = Size2D::zero();
         let position_with_overflow = self.position
                                          .to_physical(self.writing_mode, container_size)
-                                         .union(&self.overflow);
+                                         .union(&self.overflow.paint);
         let bounds = Rect::new(self.stacking_relative_position, position_with_overflow.size);
 
         let all_items = match self.display_list_building_result {

components/layout/fragment.rs

@@ -2176,7 +2176,7 @@ impl Fragment {
     pub fn compute_overflow(&self,
                             flow_size: &Size2D<Au>,
                             relative_containing_block_size: &LogicalSize<Au>)
-                            -> Rect<Au> {
+                            -> Overflow {
         let mut border_box = self.border_box.to_physical(self.style.writing_mode, *flow_size);
 
         // Relative position can cause us to draw outside our border box.
@@ -2186,31 +2186,33 @@ impl Fragment {
         let relative_position = self.relative_position(relative_containing_block_size);
         border_box =
             border_box.translate_by_size(&relative_position.to_physical(self.style.writing_mode));
-        let mut overflow = border_box;
+        let mut overflow = Overflow::from_rect(&border_box);
 
         // Box shadows cause us to draw outside our border box.
         for box_shadow in &self.style().get_effects().box_shadow.0 {
             let offset = Point2D::new(box_shadow.offset_x, box_shadow.offset_y);
             let inflation = box_shadow.spread_radius + box_shadow.blur_radius *
                 BLUR_INFLATION_FACTOR;
-            overflow = overflow.union(&border_box.translate(&offset).inflate(inflation, inflation))
+            overflow.paint = overflow.paint.union(&border_box.translate(&offset)
+                                                             .inflate(inflation, inflation))
         }
 
         // Outlines cause us to draw outside our border box.
         let outline_width = self.style.get_outline().outline_width;
         if outline_width != Au(0) {
-            overflow = overflow.union(&border_box.inflate(outline_width, outline_width))
+            overflow.paint = overflow.paint.union(&border_box.inflate(outline_width,
+                                                                      outline_width))
         }
 
         // Include the overflow of the block flow, if any.
         match self.specific {
             SpecificFragmentInfo::InlineBlock(ref info) => {
                 let block_flow = info.flow_ref.as_block();
-                overflow = overflow.union(&flow::base(block_flow).overflow);
+                overflow.union(&flow::base(block_flow).overflow);
             }
             SpecificFragmentInfo::InlineAbsolute(ref info) => {
                 let block_flow = info.flow_ref.as_block();
-                overflow = overflow.union(&flow::base(block_flow).overflow);
+                overflow.union(&flow::base(block_flow).overflow);
             }
             _ => (),
         }
@@ -2572,6 +2574,45 @@ impl WhitespaceStrippingResult {
     }
 }
 
+/// The overflow area. We need two different notions of overflow: paint overflow and scrollable
+/// overflow.
+#[derive(Copy, Clone, Debug)]
+pub struct Overflow {
+    pub scroll: Rect<Au>,
+    pub paint: Rect<Au>,
+}
+
+impl Overflow {
+    pub fn new() -> Overflow {
+        Overflow {
+            scroll: Rect::zero(),
+            paint: Rect::zero(),
+        }
+    }
+
+    pub fn from_rect(border_box: &Rect<Au>) -> Overflow {
+        Overflow {
+            scroll: *border_box,
+            paint: *border_box,
+        }
+    }
+
+    pub fn union(&mut self, other: &Overflow) {
+        self.scroll = self.scroll.union(&other.scroll);
+        self.paint = self.paint.union(&other.paint);
+    }
+
+    pub fn union_rect(&mut self, rect: &Rect<Au>) {
+        self.scroll = self.scroll.union(&rect);
+        self.paint = self.paint.union(&rect);
+    }
+
+    pub fn translate(&mut self, point: &Point2D<Au>) {
+        self.scroll = self.scroll.translate(point);
+        self.paint = self.paint.translate(point);
+    }
+}
+
 bitflags! {
     flags FragmentFlags: u8 {
         /// Whether this fragment has a layer.

components/layout/inline.rs

@@ -8,12 +8,13 @@ use app_units::Au;
 use block::AbsoluteAssignBSizesTraversal;
 use context::LayoutContext;
 use display_list_builder::{FragmentDisplayListBuilding, InlineFlowDisplayListBuilding};
-use euclid::{Point2D, Rect, Size2D};
+use euclid::{Point2D, Size2D};
 use floats::{FloatKind, Floats, PlacementInfo};
 use flow::{EarlyAbsolutePositionInfo, MutableFlowUtils, OpaqueFlow};
 use flow::{self, BaseFlow, Flow, FlowClass, ForceNonfloatedFlag, IS_ABSOLUTELY_POSITIONED};
 use flow_ref;
-use fragment::{CoordinateSystem, Fragment, FragmentBorderBoxIterator, SpecificFragmentInfo};
+use fragment::{CoordinateSystem, Fragment, FragmentBorderBoxIterator, Overflow};
+use fragment::{SpecificFragmentInfo};
 use gfx::display_list::OpaqueNode;
 use gfx::font::FontMetrics;
 use gfx::font_context::FontContext;
@@ -1756,14 +1757,13 @@ impl Flow for InlineFlow {
 
     fn repair_style(&mut self, _: &Arc<ComputedValues>) {}
 
-    fn compute_overflow(&self) -> Rect<Au> {
-        let mut overflow = Rect::zero();
+    fn compute_overflow(&self) -> Overflow {
+        let mut overflow = Overflow::new();
         let flow_size = self.base.position.size.to_physical(self.base.writing_mode);
         let relative_containing_block_size =
             &self.base.early_absolute_position_info.relative_containing_block_size;
         for fragment in &self.fragments.fragments {
-            overflow = overflow.union(&fragment.compute_overflow(&flow_size,
-                                                                 &relative_containing_block_size))
+            overflow.union(&fragment.compute_overflow(&flow_size, &relative_containing_block_size))
         }
         overflow
     }

components/layout/layout_thread.rs

@@ -865,7 +865,7 @@ impl LayoutThread {
                     if rw_data.stylist.viewport_constraints().is_some() {
                         root_flow.position.size.to_physical(root_flow.writing_mode)
                     } else {
-                        root_flow.overflow.size
+                        root_flow.overflow.scroll.size
                     }
                 };
                 let mut display_list = box DisplayList::new();

components/layout/list_item.rs

@@ -11,10 +11,11 @@ use app_units::Au;
 use block::BlockFlow;
 use context::LayoutContext;
 use display_list_builder::ListItemFlowDisplayListBuilding;
-use euclid::{Point2D, Rect};
+use euclid::Point2D;
 use floats::FloatKind;
 use flow::{Flow, FlowClass, OpaqueFlow};
 use fragment::{CoordinateSystem, Fragment, FragmentBorderBoxIterator, GeneratedContentInfo};
+use fragment::{Overflow};
 use generated_content;
 use gfx::display_list::DisplayList;
 use incremental::RESOLVE_GENERATED_CONTENT;
@@ -152,14 +153,14 @@ impl Flow for ListItemFlow {
         self.block_flow.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         let mut overflow = self.block_flow.compute_overflow();
         let flow_size = self.block_flow.base.position.size.to_physical(self.block_flow.base.writing_mode);
         let relative_containing_block_size =
             &self.block_flow.base.early_absolute_position_info.relative_containing_block_size;
 
         for fragment in &self.marker_fragments {
-            overflow = overflow.union(&fragment.compute_overflow(&flow_size, &relative_containing_block_size))
+            overflow.union(&fragment.compute_overflow(&flow_size, &relative_containing_block_size))
         }
         overflow
     }

components/layout/multicol.rs

@@ -9,11 +9,11 @@
 use app_units::Au;
 use block::BlockFlow;
 use context::LayoutContext;
-use euclid::{Point2D, Rect};
+use euclid::Point2D;
 use floats::FloatKind;
 use flow::{Flow, FlowClass, OpaqueFlow, mut_base, FragmentationContext};
 use flow_ref::{self, FlowRef};
-use fragment::{Fragment, FragmentBorderBoxIterator};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow};
 use std::cmp::{min, max};
 use std::fmt;
 use std::sync::Arc;
@@ -186,7 +186,7 @@ impl Flow for MulticolFlow {
         self.block_flow.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         self.block_flow.compute_overflow()
     }
 
@@ -264,7 +264,7 @@ impl Flow for MulticolColumnFlow {
         self.block_flow.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         self.block_flow.compute_overflow()
     }
 

components/layout/table.rs

@@ -11,10 +11,10 @@ use block::{BlockFlow, CandidateBSizeIterator, ISizeAndMarginsComputer};
 use block::{ISizeConstraintInput, ISizeConstraintSolution};
 use context::LayoutContext;
 use display_list_builder::{BlockFlowDisplayListBuilding, BorderPaintingMode};
-use euclid::{Point2D, Rect};
+use euclid::Point2D;
 use flow::{IMPACTED_BY_RIGHT_FLOATS, ImmutableFlowUtils, OpaqueFlow};
 use flow::{self, EarlyAbsolutePositionInfo, Flow, FlowClass, IMPACTED_BY_LEFT_FLOATS};
-use fragment::{Fragment, FragmentBorderBoxIterator};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow};
 use gfx::display_list::DisplayList;
 use incremental::{REFLOW, REFLOW_OUT_OF_FLOW};
 use layout_debug;
@@ -536,7 +536,7 @@ impl Flow for TableFlow {
         self.block_flow.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         self.block_flow.compute_overflow()
     }
 

components/layout/table_caption.rs

@@ -9,9 +9,9 @@
 use app_units::Au;
 use block::BlockFlow;
 use context::LayoutContext;
-use euclid::{Point2D, Rect};
+use euclid::Point2D;
 use flow::{Flow, FlowClass, OpaqueFlow};
-use fragment::{Fragment, FragmentBorderBoxIterator};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow};
 use std::fmt;
 use std::sync::Arc;
 use style::properties::ComputedValues;
@@ -83,7 +83,7 @@ impl Flow for TableCaptionFlow {
         self.block_flow.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         self.block_flow.compute_overflow()
     }
 

components/layout/table_cell.rs

@@ -13,7 +13,7 @@ use cssparser::Color;
 use display_list_builder::{BlockFlowDisplayListBuilding, BorderPaintingMode};
 use euclid::{Point2D, Rect, SideOffsets2D, Size2D};
 use flow::{Flow, FlowClass, OpaqueFlow};
-use fragment::{Fragment, FragmentBorderBoxIterator};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow};
 use gfx::display_list::DisplayList;
 use layout_debug;
 use model::MaybeAuto;
@@ -197,7 +197,7 @@ impl Flow for TableCellFlow {
         self.block_flow.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         self.block_flow.compute_overflow()
     }
 

components/layout/table_colgroup.rs

@@ -8,9 +8,9 @@
 
 use app_units::Au;
 use context::LayoutContext;
-use euclid::{Point2D, Rect};
+use euclid::Point2D;
 use flow::{BaseFlow, Flow, FlowClass, ForceNonfloatedFlag, OpaqueFlow};
-use fragment::{Fragment, FragmentBorderBoxIterator, SpecificFragmentInfo};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow, SpecificFragmentInfo};
 use layout_debug;
 use std::cmp::max;
 use std::fmt;
@@ -94,8 +94,8 @@ impl Flow for TableColGroupFlow {
 
     fn repair_style(&mut self, _: &Arc<ComputedValues>) {}
 
-    fn compute_overflow(&self) -> Rect<Au> {
-        Rect::zero()
+    fn compute_overflow(&self) -> Overflow {
+        Overflow::new()
     }
 
     fn generated_containing_block_size(&self, _: OpaqueFlow) -> LogicalSize<Au> {

components/layout/table_row.rs

@@ -11,10 +11,10 @@ use block::{BlockFlow, ISizeAndMarginsComputer};
 use context::LayoutContext;
 use cssparser::{Color, RGBA};
 use display_list_builder::{BlockFlowDisplayListBuilding, BorderPaintingMode};
-use euclid::{Point2D, Rect};
+use euclid::Point2D;
 use flow::{self, EarlyAbsolutePositionInfo, Flow, FlowClass, ImmutableFlowUtils, OpaqueFlow};
 use flow_list::MutFlowListIterator;
-use fragment::{Fragment, FragmentBorderBoxIterator};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow};
 use gfx::display_list::DisplayList;
 use layout_debug;
 use model::MaybeAuto;
@@ -439,7 +439,7 @@ impl Flow for TableRowFlow {
         self.block_flow.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         self.block_flow.compute_overflow()
     }
 

components/layout/table_rowgroup.rs

@@ -9,9 +9,9 @@
 use app_units::Au;
 use block::{BlockFlow, ISizeAndMarginsComputer};
 use context::LayoutContext;
-use euclid::{Point2D, Rect};
+use euclid::Point2D;
 use flow::{Flow, FlowClass, OpaqueFlow};
-use fragment::{Fragment, FragmentBorderBoxIterator};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow};
 use layout_debug;
 use rustc_serialize::{Encodable, Encoder};
 use std::fmt;
@@ -217,7 +217,7 @@ impl Flow for TableRowGroupFlow {
         self.block_flow.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         self.block_flow.compute_overflow()
     }
 

components/layout/table_wrapper.rs

@@ -17,11 +17,11 @@ use app_units::Au;
 use block::{AbsoluteNonReplaced, BlockFlow, FloatNonReplaced, ISizeAndMarginsComputer, ISizeConstraintInput};
 use block::{ISizeConstraintSolution, MarginsMayCollapseFlag};
 use context::LayoutContext;
-use euclid::{Point2D, Rect};
+use euclid::Point2D;
 use floats::FloatKind;
 use flow::{Flow, FlowClass, ImmutableFlowUtils};
 use flow::{IMPACTED_BY_LEFT_FLOATS, IMPACTED_BY_RIGHT_FLOATS, INLINE_POSITION_IS_STATIC, OpaqueFlow};
-use fragment::{Fragment, FragmentBorderBoxIterator};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow};
 use model::MaybeAuto;
 use std::cmp::{max, min};
 use std::fmt;
@@ -451,7 +451,7 @@ impl Flow for TableWrapperFlow {
         self.block_flow.repair_style(new_style)
     }
 
-    fn compute_overflow(&self) -> Rect<Au> {
+    fn compute_overflow(&self) -> Overflow {
         self.block_flow.compute_overflow()
     }
 

tests/html/overflow-box-shadow.html

@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<!-- Nothing on this page should be scrollable. -->
+<style>
+  body {
+    margin: 0;
+  }
+
+  .red {
+    background: red;
+    position: absolute;
+    width: 100%;
+    height: 100%;
+    overflow: hidden;
+  }
+
+  .green {
+    background: green;
+    position: absolute;
+    width: 500px;
+    height: 100%;
+    right: 0px;
+
+    width: 500px;
+    transform: translateX(250px);
+    box-shadow: 0px 0px 200px black;
+  }
+</style>
+
+<div class="red">
+  <div class="green"></div>
+</div>
+