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diff --git a/components/script/layout_interface.rs b/components/script/layout_interface.rs
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! The high-level interface from script to layout. Using this abstract interface helps reduce
+/// coupling between these two components, and enables the DOM to be placed in a separate crate
+/// from layout.
+
+use dom::bindings::js::JS;
+use dom::node::{Node, LayoutDataRef};
+
+use geom::point::Point2D;
+use geom::rect::Rect;
+use libc::c_void;
+use script_traits::{ScriptControlChan, OpaqueScriptLayoutChannel};
+use servo_msg::constellation_msg::WindowSizeData;
+use servo_util::geometry::Au;
+use std::any::{Any, AnyRefExt};
+use std::cmp;
+use std::comm::{channel, Receiver, Sender};
+use std::owned::BoxAny;
+use style::Stylesheet;
+use url::Url;
+
+use serialize::{Encodable, Encoder};
+
+/// Asynchronous messages that script can send to layout.
+pub enum Msg {
+    /// Adds the given stylesheet to the document.
+    AddStylesheetMsg(Stylesheet),
+
+    /// Requests a reflow.
+    ReflowMsg(Box<Reflow>),
+
+    /// Get an RPC interface.
+    GetRPCMsg(Sender<Box<LayoutRPC + Send>>),
+
+    /// Destroys layout data associated with a DOM node.
+    ///
+    /// TODO(pcwalton): Maybe think about batching to avoid message traffic.
+    ReapLayoutDataMsg(LayoutDataRef),
+
+    /// Requests that the layout task enter a quiescent state in which no more messages are
+    /// accepted except `ExitMsg`. A response message will be sent on the supplied channel when
+    /// this happens.
+    PrepareToExitMsg(Sender<()>),
+
+    /// Requests that the layout task immediately shut down. There must be no more nodes left after
+    /// this, or layout will crash.
+    ExitNowMsg,
+}
+
+/// Synchronous messages that script can send to layout.
+///
+/// In general, you should use messages to talk to Layout. Use the RPC interface
+/// if and only if the work is
+///
+///   1) read-only with respect to LayoutTaskData,
+///   2) small,
+//    3) and really needs to be fast.
+pub trait LayoutRPC {
+    /// Requests the dimensions of the content box, as in the `getBoundingClientRect()` call.
+    fn content_box(&self, node: TrustedNodeAddress) -> ContentBoxResponse;
+    /// Requests the dimensions of all the content boxes, as in the `getClientRects()` call.
+    fn content_boxes(&self, node: TrustedNodeAddress) -> ContentBoxesResponse;
+    /// Requests the node containing the point of interest
+    fn hit_test(&self, node: TrustedNodeAddress, point: Point2D<f32>) -> Result<HitTestResponse, ()>;
+    fn mouse_over(&self, node: TrustedNodeAddress, point: Point2D<f32>) -> Result<MouseOverResponse, ()>;
+}
+
+/// The address of a node known to be valid. These must only be sent from content -> layout,
+/// because we do not trust layout.
+pub struct TrustedNodeAddress(pub *const c_void);
+
+impl<S: Encoder<E>, E> Encodable<S, E> for TrustedNodeAddress {
+    fn encode(&self, s: &mut S) -> Result<(), E> {
+        let TrustedNodeAddress(addr) = *self;
+        let node = addr as *const Node;
+        unsafe {
+            JS::from_raw(node).encode(s)
+        }
+    }
+}
+
+/// The address of a node. Layout sends these back. They must be validated via
+/// `from_untrusted_node_address` before they can be used, because we do not trust layout.
+pub type UntrustedNodeAddress = *const c_void;
+
+pub struct ContentBoxResponse(pub Rect<Au>);
+pub struct ContentBoxesResponse(pub Vec<Rect<Au>>);
+pub struct HitTestResponse(pub UntrustedNodeAddress);
+pub struct MouseOverResponse(pub Vec<UntrustedNodeAddress>);
+
+/// Determines which part of the
+#[deriving(PartialEq, PartialOrd, Eq, Ord, Encodable)]
+pub enum DocumentDamageLevel {
+    /// Reflow, but do not perform CSS selector matching.
+    ReflowDocumentDamage,
+    /// Perform CSS selector matching and reflow.
+    MatchSelectorsDocumentDamage,
+    /// Content changed; set full style damage and do the above.
+    ContentChangedDocumentDamage,
+}
+
+impl DocumentDamageLevel {
+    /// Sets this damage to the maximum of this damage and the given damage.
+    pub fn add(&mut self, new_damage: DocumentDamageLevel) {
+        *self = cmp::max(*self, new_damage);
+    }
+}
+
+/// What parts of the document have changed, as far as the script task can tell.
+///
+/// Note that this is fairly coarse-grained and is separate from layout's notion of the document
+#[deriving(Encodable)]
+pub struct DocumentDamage {
+    /// The topmost node in the tree that has changed.
+    pub root: TrustedNodeAddress,
+    /// The amount of damage that occurred.
+    pub level: DocumentDamageLevel,
+}
+
+/// Why we're doing reflow.
+#[deriving(PartialEq)]
+pub enum ReflowGoal {
+    /// We're reflowing in order to send a display list to the screen.
+    ReflowForDisplay,
+    /// We're reflowing in order to satisfy a script query. No display list will be created.
+    ReflowForScriptQuery,
+}
+
+/// Information needed for a reflow.
+pub struct Reflow {
+    /// The document node.
+    pub document_root: TrustedNodeAddress,
+    /// The style changes that need to be done.
+    pub damage: DocumentDamage,
+    /// The goal of reflow: either to render to the screen or to flush layout info for script.
+    pub goal: ReflowGoal,
+    /// The URL of the page.
+    pub url: Url,
+    /// The channel through which messages can be sent back to the script task.
+    pub script_chan: ScriptControlChan,
+    /// The current window size.
+    pub window_size: WindowSizeData,
+    /// The channel that we send a notification to.
+    pub script_join_chan: Sender<()>,
+    /// Unique identifier
+    pub id: uint
+}
+
+/// Encapsulates a channel to the layout task.
+#[deriving(Clone)]
+pub struct LayoutChan(pub Sender<Msg>);
+
+impl LayoutChan {
+    pub fn new() -> (Receiver<Msg>, LayoutChan) {
+        let (chan, port) = channel();
+        (port, LayoutChan(chan))
+    }
+}
+
+/// A trait to manage opaque references to script<->layout channels without needing
+/// to expose the message type to crates that don't need to know about them.
+pub trait ScriptLayoutChan {
+    fn new(sender: Sender<Msg>, receiver: Receiver<Msg>) -> Self;
+    fn sender(&self) -> Sender<Msg>;
+    fn receiver(self) -> Receiver<Msg>;
+}
+
+impl ScriptLayoutChan for OpaqueScriptLayoutChannel {
+    fn new(sender: Sender<Msg>, receiver: Receiver<Msg>) -> OpaqueScriptLayoutChannel {
+        let inner = (box sender as Box<Any+Send>, box receiver as Box<Any+Send>);
+        OpaqueScriptLayoutChannel(inner)
+    }
+
+    fn sender(&self) -> Sender<Msg> {
+        let &OpaqueScriptLayoutChannel((ref sender, _)) = self;
+        (*sender.downcast_ref::<Sender<Msg>>().unwrap()).clone()
+    }
+
+    fn receiver(self) -> Receiver<Msg> {
+        let OpaqueScriptLayoutChannel((_, receiver)) = self;
+        *receiver.downcast::<Receiver<Msg>>().unwrap()
+    }
+}
+
+#[test]
+fn test_add_damage() {
+    fn assert_add(mut a: DocumentDamageLevel, b: DocumentDamageLevel,
+                  result: DocumentDamageLevel) {
+        a.add(b);
+        assert!(a == result);
+    }
+
+    assert_add(ReflowDocumentDamage, ReflowDocumentDamage, ReflowDocumentDamage);
+    assert_add(ContentChangedDocumentDamage, ContentChangedDocumentDamage, ContentChangedDocumentDamage);
+    assert_add(ReflowDocumentDamage, MatchSelectorsDocumentDamage, MatchSelectorsDocumentDamage);
+    assert_add(MatchSelectorsDocumentDamage, ReflowDocumentDamage, MatchSelectorsDocumentDamage);
+    assert_add(ReflowDocumentDamage, ContentChangedDocumentDamage, ContentChangedDocumentDamage);
+    assert_add(ContentChangedDocumentDamage, ReflowDocumentDamage, ContentChangedDocumentDamage);
+    assert_add(MatchSelectorsDocumentDamage, ContentChangedDocumentDamage, ContentChangedDocumentDamage);
+    assert_add(ContentChangedDocumentDamage, MatchSelectorsDocumentDamage, ContentChangedDocumentDamage);
+}