Separate the DOM and layout into separate crates.

src/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::node::{AbstractNode, ScriptView};
+use script_task::ScriptMsg;
+
+use core::comm::{Chan, SharedChan};
+use geom::rect::Rect;
+use geom::size::Size2D;
+use gfx::geometry::Au;
+use newcss::stylesheet::Stylesheet;
+use std::net::url::Url;
+
+/// Asynchronous messages that script can send to layout.
+///
+/// FIXME(pcwalton): I think this should probably be merged with `LayoutQuery` below.
+pub enum Msg {
+    /// Adds the given stylesheet to the document.
+    AddStylesheetMsg(Stylesheet),
+
+    /// Requests a reflow.
+    ///
+    /// FIXME(pcwalton): Call this `reflow` instead?
+    BuildMsg(~BuildData),
+
+    /// Performs a synchronous layout request.
+    ///
+    /// FIXME(pcwalton): As noted below, this isn't very type safe.
+    QueryMsg(LayoutQuery, Chan<Result<LayoutResponse,()>>),
+
+    /// Requests that the layout task shut down and exit.
+    ExitMsg,
+}
+
+/// Synchronous messages that script can send to layout.
+pub enum LayoutQuery {
+    /// Requests the dimensions of the content box, as in the `getBoundingClientRect()` call.
+    ContentBoxQuery(AbstractNode<ScriptView>),
+    /// Requests the dimensions of all the content boxes, as in the `getClientRects()` call.
+    ContentBoxesQuery(AbstractNode<ScriptView>),
+}
+
+/// The reply of a synchronous message from script to layout.
+///
+/// FIXME(pcwalton): This isn't very type safe. Maybe `LayoutQuery` objects should include
+/// response channels?
+pub enum LayoutResponse {
+    /// A response to the `ContentBoxQuery` message.
+    ContentBoxResponse(Rect<Au>),
+    /// A response to the `ContentBoxesQuery` message.
+    ContentBoxesResponse(~[Rect<Au>]),
+}
+
+/// Dirty bits for layout.
+pub enum Damage {
+    /// The document is clean; nothing needs to be done.
+    NoDamage,
+    /// Reflow, but do not perform CSS selector matching.
+    ReflowDamage,
+    /// Perform CSS selector matching and reflow.
+    MatchSelectorsDamage,
+}
+
+impl Damage {
+    /// Sets this damage to the maximum of this damage and the given damage.
+    ///
+    /// FIXME(pcwalton): This could be refactored to use `max` and the `Ord` trait, and this
+    /// function removed.
+    fn add(&mut self, new_damage: Damage) {
+        match (*self, new_damage) {
+            (NoDamage, _) => *self = new_damage,
+            (ReflowDamage, NoDamage) => *self = ReflowDamage,
+            (ReflowDamage, new_damage) => *self = new_damage,
+            (MatchSelectorsDamage, _) => *self = MatchSelectorsDamage
+        }
+    }
+}
+
+/// Information needed for a reflow.
+pub struct BuildData {
+    node: AbstractNode<ScriptView>,
+    /// What reflow needs to be done.
+    damage: Damage,
+    /// The URL of the page.
+    url: Url,
+    /// The channel through which messages can be sent back to the script task.
+    script_chan: SharedChan<ScriptMsg>,
+    /// The current window size.
+    window_size: Size2D<uint>,
+    script_join_chan: Chan<()>,
+}
+
+/// Encapsulates a channel to the layout task.
+#[deriving(Clone)]
+pub struct LayoutTask {
+    chan: SharedChan<Msg>,
+}
+