Remove concept of Layers from Servo

Layers were a feature of the legacy drawing path. If we re-add them at
some point, it probably makes more sense to make them a product of
display list inspection.

This change also remove a bunch of dead painting code.

7 files changed, 26 insertions, 153 deletions

diff --git a/components/layout/block.rs b/components/layout/block.rs
index 2011c50c181..b860d8347d1 100644
--- a/components/layout/block.rs
+++ b/components/layout/block.rs
@@ -36,15 +36,14 @@ use floats::{ClearType, FloatKind, Floats, PlacementInfo};
 use flow::{self, BaseFlow, EarlyAbsolutePositionInfo, Flow, FlowClass, ForceNonfloatedFlag};
 use flow::{BLOCK_POSITION_IS_STATIC, CLEARS_LEFT, CLEARS_RIGHT};
 use flow::{CONTAINS_TEXT_OR_REPLACED_FRAGMENTS, INLINE_POSITION_IS_STATIC};
-use flow::{FragmentationContext, NEEDS_LAYER, PreorderFlowTraversal};
+use flow::{FragmentationContext, PreorderFlowTraversal};
 use flow::{ImmutableFlowUtils, LateAbsolutePositionInfo, MutableFlowUtils, OpaqueFlow};
 use flow::IS_ABSOLUTELY_POSITIONED;
 use flow_list::FlowList;
 use flow_ref::FlowRef;
-use fragment::{CoordinateSystem, Fragment, FragmentBorderBoxIterator, HAS_LAYER, Overflow};
+use fragment::{CoordinateSystem, Fragment, FragmentBorderBoxIterator, Overflow};
 use fragment::SpecificFragmentInfo;
 use gfx::display_list::{ClippingRegion, StackingContext};
-use gfx_traits::LayerId;
 use gfx_traits::print_tree::PrintTree;
 use layout_debug;
 use model::{CollapsibleMargins, IntrinsicISizes, MarginCollapseInfo, MaybeAuto};
@@ -57,12 +56,12 @@ use std::cmp::{max, min};
 use std::fmt;
 use std::sync::Arc;
 use style::computed_values::{border_collapse, box_sizing, display, float, overflow_x, overflow_y};
-use style::computed_values::{position, text_align, transform_style};
+use style::computed_values::{position, text_align};
 use style::context::{SharedStyleContext, StyleContext};
 use style::logical_geometry::{LogicalPoint, LogicalRect, LogicalSize, WritingMode};
 use style::properties::ServoComputedValues;
-use style::values::computed::{LengthOrNone, LengthOrPercentageOrNone};
-use style::values::computed::{LengthOrPercentage, LengthOrPercentageOrAuto};
+use style::values::computed::{LengthOrPercentageOrNone, LengthOrPercentage};
+use style::values::computed::LengthOrPercentageOrAuto;
 use util::clamp;
 
 /// Information specific to floated blocks.
@@ -793,8 +792,6 @@ impl BlockFlow {
         let mut break_at = None;
         let content_box = self.fragment.content_box();
         if self.base.restyle_damage.contains(REFLOW) {
-            self.determine_if_layer_needed();
-
             // Our current border-box position.
             let mut cur_b = Au(0);
 
@@ -1679,34 +1676,6 @@ impl BlockFlow {
         self.base.flags = flags
     }
 
-    fn determine_if_layer_needed(&mut self) {
-        // Fixed position layers get layers.
-        if self.base.flags.contains(IS_ABSOLUTELY_POSITIONED) && self.is_fixed() {
-            self.base.flags.insert(NEEDS_LAYER);
-            return
-        }
-
-        // This flow needs a layer if it has a 3d transform, or provides perspective
-        // to child layers. See http://dev.w3.org/csswg/css-transforms/#3d-rendering-contexts.
-        let has_3d_transform = self.fragment.style().transform_requires_layer();
-        let has_perspective = self.fragment.style().get_effects().perspective !=
-            LengthOrNone::None;
-
-        if has_3d_transform || has_perspective {
-            self.base.flags.insert(NEEDS_LAYER);
-            return
-        }
-
-        match (self.fragment.style().get_box().overflow_x,
-               self.fragment.style().get_box().overflow_y.0) {
-            (overflow_x::T::auto, _) | (overflow_x::T::scroll, _) |
-            (_, overflow_x::T::auto) | (_, overflow_x::T::scroll) => {
-                self.base.flags.insert(NEEDS_LAYER);
-            }
-            _ => {}
-        }
-    }
-
     pub fn block_stacking_context_type(&self) -> BlockStackingContextType {
         if self.fragment.establishes_stacking_context() {
             return BlockStackingContextType::StackingContext
@@ -1956,10 +1925,6 @@ impl Flow for BlockFlow {
     }
 
     fn compute_absolute_position(&mut self, _layout_context: &SharedLayoutContext) {
-        if self.base.flags.contains(NEEDS_LAYER) {
-            self.fragment.flags.insert(HAS_LAYER)
-        }
-
         // FIXME (mbrubeck): Get the real container size, taking the container writing mode into
         // account.  Must handle vertical writing modes.
         let container_size = Size2D::new(self.base.block_container_inline_size, Au(0));
@@ -1968,8 +1933,6 @@ impl Flow for BlockFlow {
             self.base.clip = ClippingRegion::max();
         }
 
-        let transform_style = self.fragment.style().get_used_transform_style();
-
         if self.base.flags.contains(IS_ABSOLUTELY_POSITIONED) {
             // `overflow: auto` and `overflow: scroll` force creation of layers, since we can only
             // scroll layers.
@@ -2103,16 +2066,6 @@ impl Flow for BlockFlow {
 
         // Process children.
         for kid in self.base.child_iter_mut() {
-            // If this layer preserves the 3d context of children,
-            // then children will need a render layer.
-            // TODO(gw): This isn't always correct. In some cases
-            // this may create extra layers than needed. I think
-            // there are also some edge cases where children don't
-            // get a layer when they should.
-            if transform_style == transform_style::T::preserve_3d {
-                flow::mut_base(kid).flags.insert(NEEDS_LAYER);
-            }
-
             if flow::base(kid).flags.contains(INLINE_POSITION_IS_STATIC) ||
                     flow::base(kid).flags.contains(BLOCK_POSITION_IS_STATIC) {
                 let kid_base = flow::mut_base(kid);
@@ -2177,14 +2130,6 @@ impl Flow for BlockFlow {
         (self.fragment.border_box - self.fragment.style().logical_border_width()).size
     }
 
-    fn layer_id(&self) -> LayerId {
-        self.fragment.layer_id()
-    }
-
-    fn layer_id_for_overflow_scroll(&self) -> LayerId {
-        self.fragment.layer_id_for_overflow_scroll()
-    }
-
     fn is_absolute_containing_block(&self) -> bool {
         self.contains_positioned_fragments()
     }
diff --git a/components/layout/context.rs b/components/layout/context.rs
index 7125c6ab44d..17a484e2930 100644
--- a/components/layout/context.rs
+++ b/components/layout/context.rs
@@ -7,13 +7,10 @@
 // for thread_local
 #![allow(unsafe_code)]
 
-use app_units::Au;
-use euclid::Rect;
 use fnv::FnvHasher;
 use gfx::display_list::WebRenderImageInfo;
 use gfx::font_cache_thread::FontCacheThread;
 use gfx::font_context::FontContext;
-use gfx_traits::LayerId;
 use heapsize::HeapSizeOf;
 use ipc_channel::ipc;
 use net_traits::image::base::Image;
@@ -87,9 +84,6 @@ pub struct SharedLayoutContext {
     /// Interface to the font cache thread.
     pub font_cache_thread: Mutex<FontCacheThread>,
 
-    /// The visible rects for each layer, as reported to us by the compositor.
-    pub visible_rects: Arc<HashMap<LayerId, Rect<Au>, BuildHasherDefault<FnvHasher>>>,
-
     /// A cache of WebRender image info.
     pub webrender_image_cache: Arc<RwLock<HashMap<(Url, UsePlaceholder),
                                                   WebRenderImageInfo,
diff --git a/components/layout/display_list_builder.rs b/components/layout/display_list_builder.rs
index 2574d345466..e714df23314 100644
--- a/components/layout/display_list_builder.rs
+++ b/components/layout/display_list_builder.rs
@@ -19,13 +19,13 @@ use euclid::{Matrix4D, Point2D, Radians, Rect, SideOffsets2D, Size2D};
 use flex::FlexFlow;
 use flow::{BaseFlow, Flow, IS_ABSOLUTELY_POSITIONED};
 use flow_ref;
-use fragment::{CoordinateSystem, Fragment, HAS_LAYER, ImageFragmentInfo, ScannedTextFragmentInfo};
+use fragment::{CoordinateSystem, Fragment, ImageFragmentInfo, ScannedTextFragmentInfo};
 use fragment::SpecificFragmentInfo;
 use gfx::display_list::{BLUR_INFLATION_FACTOR, BaseDisplayItem, BorderDisplayItem};
 use gfx::display_list::{BorderRadii, BoxShadowClipMode, BoxShadowDisplayItem, ClippingRegion};
 use gfx::display_list::{DisplayItem, DisplayItemMetadata, DisplayListSection, GradientDisplayItem};
 use gfx::display_list::{GradientStop, IframeDisplayItem, ImageDisplayItem, WebGLDisplayItem};
-use gfx::display_list::{LayerInfo, LineDisplayItem, OpaqueNode};
+use gfx::display_list::{LineDisplayItem, OpaqueNode};
 use gfx::display_list::{SolidColorDisplayItem, StackingContext, StackingContextType};
 use gfx::display_list::{TextDisplayItem, TextOrientation, WebRenderImageInfo};
 use gfx_traits::{ScrollPolicy, StackingContextId, color};
@@ -1410,12 +1410,6 @@ impl FragmentDisplayListBuilding for Fragment {
             filters.push(Filter::Opacity(effects.opacity))
         }
 
-        let layer_info = if self.flags.contains(HAS_LAYER) {
-            Some(LayerInfo::new(self.layer_id(), scroll_policy, None, color::transparent()))
-        } else {
-            None
-        };
-
         let transform_style = self.style().get_used_transform_style();
         let establishes_3d_context = scrolls_overflow_area ||
             transform_style == transform_style::T::flat;
@@ -1436,7 +1430,7 @@ impl FragmentDisplayListBuilding for Fragment {
                              transform,
                              perspective,
                              establishes_3d_context,
-                             layer_info,
+                             scroll_policy,
                              scroll_id)
     }
 
diff --git a/components/layout/flow.rs b/components/layout/flow.rs
index ea5d61e4cf0..0e92de265d1 100644
--- a/components/layout/flow.rs
+++ b/components/layout/flow.rs
@@ -35,7 +35,7 @@ use flow_list::{FlowList, MutFlowListIterator};
 use flow_ref::{self, FlowRef, WeakFlowRef};
 use fragment::{Fragment, FragmentBorderBoxIterator, Overflow, SpecificFragmentInfo};
 use gfx::display_list::{ClippingRegion, StackingContext};
-use gfx_traits::{LayerId, LayerType, StackingContextId};
+use gfx_traits::StackingContextId;
 use gfx_traits::print_tree::PrintTree;
 use inline::InlineFlow;
 use model::{CollapsibleMargins, IntrinsicISizes, MarginCollapseInfo};
@@ -399,16 +399,6 @@ pub trait Flow: fmt::Debug + Sync + Send + 'static {
     /// implications because this can be called on parents concurrently from descendants!
     fn generated_containing_block_size(&self, _: OpaqueFlow) -> LogicalSize<Au>;
 
-    /// Returns a layer ID for the given fragment.
-    fn layer_id(&self) -> LayerId {
-        LayerId::new_of_type(LayerType::FragmentBody, base(self).flow_id())
-    }
-
-    /// Returns a layer ID for the given fragment.
-    fn layer_id_for_overflow_scroll(&self) -> LayerId {
-        LayerId::new_of_type(LayerType::OverflowScroll, base(self).flow_id())
-    }
-
     /// Attempts to perform incremental fixup of this flow by replacing its fragment's style with
     /// the new style. This can only succeed if the flow has exactly one fragment.
     fn repair_style(&mut self, new_style: &Arc<ServoComputedValues>);
@@ -634,10 +624,6 @@ bitflags! {
     #[doc = "Flags used in flows."]
     pub flags FlowFlags: u32 {
         // text align flags
-        #[doc = "Whether this flow must have its own layer. Even if this flag is not set, it might"]
-        #[doc = "get its own layer if it's deemed to be likely to overlap flows with their own"]
-        #[doc = "layer."]
-        const NEEDS_LAYER = 0b0000_0000_0000_0000_0010_0000,
         #[doc = "Whether this flow is absolutely positioned. This is checked all over layout, so a"]
         #[doc = "virtual call is too expensive."]
         const IS_ABSOLUTELY_POSITIONED = 0b0000_0000_0000_0000_0100_0000,
diff --git a/components/layout/fragment.rs b/components/layout/fragment.rs
index 7693e111347..68faff25430 100644
--- a/components/layout/fragment.rs
+++ b/components/layout/fragment.rs
@@ -17,7 +17,7 @@ use gfx;
 use gfx::display_list::{BLUR_INFLATION_FACTOR, OpaqueNode};
 use gfx::text::glyph::ByteIndex;
 use gfx::text::text_run::{TextRun, TextRunSlice};
-use gfx_traits::{FragmentType, LayerId, LayerType, StackingContextId};
+use gfx_traits::{FragmentType, StackingContextId};
 use inline::{FIRST_FRAGMENT_OF_ELEMENT, InlineFragmentContext, InlineFragmentNodeInfo};
 use inline::{InlineMetrics, LAST_FRAGMENT_OF_ELEMENT, LineMetrics};
 use ipc_channel::ipc::IpcSender;
@@ -48,7 +48,7 @@ use style::dom::TRestyleDamage;
 use style::logical_geometry::{LogicalMargin, LogicalRect, LogicalSize, WritingMode};
 use style::properties::ServoComputedValues;
 use style::str::char_is_whitespace;
-use style::values::computed::{LengthOrPercentage, LengthOrPercentageOrAuto};
+use style::values::computed::{LengthOrNone, LengthOrPercentage, LengthOrPercentageOrAuto};
 use style::values::computed::LengthOrPercentageOrNone;
 use text;
 use text::TextRunScanner;
@@ -122,9 +122,6 @@ pub struct Fragment {
     /// The pseudo-element that this fragment represents.
     pub pseudo: PseudoElementType<()>,
 
-    /// Various flags for this fragment.
-    pub flags: FragmentFlags,
-
     /// A debug ID that is consistent for the life of this fragment (via transform etc).
     /// This ID should not be considered stable across multiple layouts or fragment
     /// manipulations.
@@ -919,7 +916,6 @@ impl Fragment {
             specific: specific,
             inline_context: None,
             pseudo: node.get_pseudo_element_type().strip(),
-            flags: FragmentFlags::empty(),
             debug_id: DebugId::new(),
             stacking_context_id: StackingContextId::new(0),
         }
@@ -948,7 +944,6 @@ impl Fragment {
             specific: specific,
             inline_context: None,
             pseudo: pseudo,
-            flags: FragmentFlags::empty(),
             debug_id: DebugId::new(),
             stacking_context_id: StackingContextId::new(0),
         }
@@ -976,7 +971,6 @@ impl Fragment {
             specific: info,
             inline_context: self.inline_context.clone(),
             pseudo: self.pseudo.clone(),
-            flags: FragmentFlags::empty(),
             debug_id: self.debug_id.clone(),
             stacking_context_id: StackingContextId::new(0),
         }
@@ -2535,9 +2529,6 @@ impl Fragment {
             _ => {}
         }
 
-        if self.flags.contains(HAS_LAYER) {
-            return true
-        }
         if self.style().get_effects().opacity != 1.0 {
             return true
         }
@@ -2550,6 +2541,18 @@ impl Fragment {
         if self.style().get_effects().transform.0.is_some() {
             return true
         }
+
+        // TODO(mrobinson): Determine if this is necessary, since blocks with
+        // transformations already create stacking contexts.
+        if self.style().get_effects().perspective != LengthOrNone::None {
+            return true
+        }
+
+        // Fixed position blocks always create stacking contexts.
+        if self.style.get_box().position == position::T::fixed {
+            return true
+        }
+
         match self.style().get_used_transform_style() {
             transform_style::T::flat | transform_style::T::preserve_3d => {
                 return true
@@ -2874,21 +2877,6 @@ impl Fragment {
         }
     }
 
-    pub fn layer_id(&self) -> LayerId {
-        let layer_type = match self.pseudo {
-            PseudoElementType::Normal => LayerType::FragmentBody,
-            PseudoElementType::Before(_) => LayerType::BeforePseudoContent,
-            PseudoElementType::After(_) => LayerType::AfterPseudoContent,
-            PseudoElementType::DetailsSummary(_) => LayerType::FragmentBody,
-            PseudoElementType::DetailsContent(_) => LayerType::FragmentBody,
-        };
-        LayerId::new_of_type(layer_type, self.node.id() as usize)
-    }
-
-    pub fn layer_id_for_overflow_scroll(&self) -> LayerId {
-        LayerId::new_of_type(LayerType::OverflowScroll, self.node.id() as usize)
-    }
-
     /// Returns true if any of the inline styles associated with this fragment have
     /// `vertical-align` set to `top` or `bottom`.
     pub fn is_vertically_aligned_to_top_or_bottom(&self) -> bool {
@@ -3094,13 +3082,6 @@ impl Overflow {
     }
 }
 
-bitflags! {
-    pub flags FragmentFlags: u8 {
-        /// Whether this fragment has a layer.
-        const HAS_LAYER = 0x01,
-    }
-}
-
 /// Specified distances from the margin edge of a block to its content in the inline direction.
 /// These are returned by `guess_inline_content_edge_offsets()` and are used in the float placement
 /// speculation logic.
diff --git a/components/layout/query.rs b/components/layout/query.rs
index 822377ef86f..a71bc246113 100644
--- a/components/layout/query.rs
+++ b/components/layout/query.rs
@@ -12,14 +12,13 @@ use euclid::size::Size2D;
 use flow::{self, Flow};
 use fragment::{Fragment, FragmentBorderBoxIterator, SpecificFragmentInfo};
 use gfx::display_list::{DisplayItemMetadata, DisplayList, OpaqueNode, ScrollOffsetMap};
-use gfx_traits::LayerId;
 use ipc_channel::ipc::IpcSender;
 use opaque_node::OpaqueNodeMethods;
 use script_layout_interface::rpc::{ContentBoxResponse, ContentBoxesResponse};
 use script_layout_interface::rpc::{HitTestResponse, LayoutRPC};
 use script_layout_interface::rpc::{MarginStyleResponse, NodeGeometryResponse};
-use script_layout_interface::rpc::{NodeLayerIdResponse, NodeOverflowResponse};
-use script_layout_interface::rpc::{OffsetParentResponse, ResolvedStyleResponse};
+use script_layout_interface::rpc::{NodeOverflowResponse, OffsetParentResponse};
+use script_layout_interface::rpc::ResolvedStyleResponse;
 use script_layout_interface::wrapper_traits::{LayoutNode, ThreadSafeLayoutNode};
 use script_traits::LayoutMsg as ConstellationMsg;
 use script_traits::UntrustedNodeAddress;
@@ -61,8 +60,6 @@ pub struct LayoutThreadData {
     /// A queued response for the client {top, left, width, height} of a node in pixels.
     pub client_rect_response: Rect<i32>,
 
-    pub layer_id_response: Option<LayerId>,
-
     /// A queued response for the node at a given point
     pub hit_test_response: (Option<DisplayItemMetadata>, bool),
 
@@ -180,13 +177,6 @@ impl LayoutRPC for LayoutRPCImpl {
         }
     }
 
-    fn node_layer_id(&self) -> NodeLayerIdResponse {
-        NodeLayerIdResponse {
-            layer_id: self.0.lock().unwrap().layer_id_response
-                          .expect("layer_id is not correctly fetched, see PR #9968")
-        }
-    }
-
     /// Retrieves the resolved value for a CSS style property.
     fn resolved_style(&self) -> ResolvedStyleResponse {
         let &LayoutRPCImpl(ref rw_data) = self;
@@ -587,11 +577,6 @@ pub fn process_node_geometry_request<N: LayoutNode>(requested_node: N, layout_ro
     iterator.client_rect
 }
 
-pub fn process_node_layer_id_request<N: LayoutNode>(requested_node: N) -> LayerId {
-    let layout_node = requested_node.to_threadsafe();
-    layout_node.layer_id()
-}
-
 pub fn process_node_scroll_area_request< N: LayoutNode>(requested_node: N, layout_root: &mut Flow)
         -> Rect<i32> {
     let mut iterator = UnioningFragmentScrollAreaIterator::new(requested_node.opaque());
diff --git a/components/layout/webrender_helpers.rs b/components/layout/webrender_helpers.rs
index 6e8821fc572..19e645c80a5 100644
--- a/components/layout/webrender_helpers.rs
+++ b/components/layout/webrender_helpers.rs
@@ -26,7 +26,6 @@ trait WebRenderStackingContextConverter {
                                 pipeline_id: webrender_traits::PipelineId,
                                 epoch: webrender_traits::Epoch,
                                 scroll_layer_id: Option<webrender_traits::ScrollLayerId>,
-                                scroll_policy: ScrollPolicy,
                                 frame_builder: &mut WebRenderFrameBuilder)
                                 -> webrender_traits::StackingContextId;
 
@@ -36,7 +35,6 @@ trait WebRenderStackingContextConverter {
                                          pipeline_id: webrender_traits::PipelineId,
                                          epoch: webrender_traits::Epoch,
                                          scroll_layer_id: Option<webrender_traits::ScrollLayerId>,
-                                         scroll_policy: ScrollPolicy,
                                          builder: &mut webrender_traits::DisplayListBuilder,
                                          frame_builder: &mut WebRenderFrameBuilder,
                                          force_positioned_stacking_level: bool);
@@ -256,7 +254,6 @@ impl WebRenderStackingContextConverter for StackingContext {
                                          pipeline_id: webrender_traits::PipelineId,
                                          epoch: webrender_traits::Epoch,
                                          scroll_layer_id: Option<webrender_traits::ScrollLayerId>,
-                                         scroll_policy: ScrollPolicy,
                                          builder: &mut webrender_traits::DisplayListBuilder,
                                          frame_builder: &mut WebRenderFrameBuilder,
                                          _force_positioned_stacking_level: bool) {
@@ -278,7 +275,6 @@ impl WebRenderStackingContextConverter for StackingContext {
                                                               pipeline_id,
                                                               epoch,
                                                               scroll_layer_id_for_children,
-                                                              scroll_policy,
                                                               frame_builder);
                     builder.push_stacking_context(stacking_context_id);
 
@@ -295,14 +291,9 @@ impl WebRenderStackingContextConverter for StackingContext {
                                 pipeline_id: webrender_traits::PipelineId,
                                 epoch: webrender_traits::Epoch,
                                 scroll_layer_id: Option<webrender_traits::ScrollLayerId>,
-                                mut scroll_policy: ScrollPolicy,
                                 frame_builder: &mut WebRenderFrameBuilder)
                                 -> webrender_traits::StackingContextId {
-        if let Some(ref layer_info) = self.layer_info {
-            scroll_policy = layer_info.scroll_policy
-        }
-
-        let webrender_scroll_policy = match scroll_policy {
+        let webrender_scroll_policy = match self.scroll_policy {
             ScrollPolicy::Scrollable => webrender_traits::ScrollPolicy::Scrollable,
             ScrollPolicy::FixedPosition => webrender_traits::ScrollPolicy::Fixed,
         };
@@ -353,7 +344,6 @@ impl WebRenderStackingContextConverter for StackingContext {
                                                pipeline_id,
                                                epoch,
                                                None,
-                                               scroll_policy,
                                                &mut inner_builder,
                                                frame_builder,
                                                false);
@@ -367,7 +357,6 @@ impl WebRenderStackingContextConverter for StackingContext {
                                                pipeline_id,
                                                epoch,
                                                scroll_layer_id,
-                                               scroll_policy,
                                                &mut builder,
                                                frame_builder,
                                                false);
@@ -397,7 +386,6 @@ impl WebRenderDisplayListConverter for DisplayList {
                                                       pipeline_id,
                                                       epoch,
                                                       scroll_layer_id,
-                                                      ScrollPolicy::Scrollable,
                                                       frame_builder)
             }
             _ => unreachable!("DisplayList did not start with StackingContext."),