content, layout: Very, very early beginnings of support for incremental reflow.

Don't perform CSS selector matching when the window is resized.

src/servo/content/content_task.rs

@@ -9,7 +9,8 @@ use dom::node::{Node, NodeScope, define_bindings};
 use dom::event::{Event, ResizeEvent, ReflowEvent};
 use dom::window::Window;
 use layout::layout_task;
-use layout::layout_task::{AddStylesheet, BuildData, BuildMsg, LayoutTask};
+use layout::layout_task::{AddStylesheet, BuildData, BuildMsg, Damage, LayoutTask};
+use layout::layout_task::{MatchSelectorsDamage, NoDamage, ReflowDamage};
 
 use core::comm::{Port, Chan, listen, select2};
 use core::either;
@@ -96,6 +97,9 @@ pub struct Content {
     resource_task: ResourceTask,
 
     compartment: Option<compartment>,
+
+    // What parts of layout are dirty.
+    mut damage: Damage,
 }
 
 fn Content(layout_task: LayoutTask, 
@@ -136,7 +140,9 @@ fn Content(layout_task: LayoutTask,
         window_size : Size2D(800u, 600u),
 
         resource_task : resource_task,
-        compartment : compartment
+        compartment : compartment,
+
+        damage : MatchSelectorsDamage,
     };
 
     cx.set_cx_private(ptr::to_unsafe_ptr(&*content) as *());
@@ -196,7 +202,10 @@ impl Content {
 
             let document = Document(root, self.scope);
             let window   = Window(self.control_chan.clone());
+
+            self.damage.add(MatchSelectorsDamage);
             self.relayout(&document, &url);
+
             self.document = Some(@move document);
             self.window   = Some(@move window);
             self.doc_url = Some(move url);
@@ -302,7 +311,8 @@ impl Content {
             url: copy *doc_url,
             dom_event_chan: self.event_chan.clone(),
             window_size: self.window_size,
-            content_join_chan: move join_chan
+            content_join_chan: move join_chan,
+            damage: replace(&mut self.damage, NoDamage),
         };
 
         self.layout_task.send(BuildMsg(move data));
@@ -331,6 +341,7 @@ impl Content {
         match event {
           ResizeEvent(new_width, new_height, response_chan) => {
             debug!("content got resize event: %u, %u", new_width, new_height);
+            self.damage.add(ReflowDamage);
             self.window_size = Size2D(new_width, new_height);
             match copy self.document {
                 None => {
@@ -346,6 +357,7 @@ impl Content {
           }
           ReflowEvent => {
             debug!("content got reflow event");
+            self.damage.add(MatchSelectorsDamage);
             match copy self.document {
                 None => {
                     // Nothing to do.

src/servo/layout/layout_task.rs

@@ -57,12 +57,31 @@ pub enum Msg {
     ExitMsg
 }
 
+// Dirty bits for layout.
+pub enum Damage {
+    NoDamage,               // Document is clean; do nothing.
+    ReflowDamage,           // Reflow; don't perform CSS selector matching.
+    MatchSelectorsDamage,   // Perform CSS selector matching and reflow.
+}
+
+impl Damage {
+    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
+        }
+    }
+}
+
 struct BuildData {
     node: Node,
     url: Url,
     dom_event_chan: pipes::SharedChan<Event>,
     window_size: Size2D<uint>,
-    content_join_chan: pipes::Chan<()>
+    content_join_chan: pipes::Chan<()>,
+    damage: Damage,
 }
 
 fn LayoutTask(render_task: RenderTask,
@@ -147,7 +166,6 @@ impl Layout {
     }
 
     fn handle_build(data: BuildData) {
-
         let node = &data.node;
         // FIXME: Bad copy
         let doc_url = copy data.url;
@@ -155,6 +173,7 @@ impl Layout {
         let dom_event_chan = data.dom_event_chan.clone();
 
         debug!("layout: received layout request for: %s", doc_url.to_str());
+        debug!("layout: damage is %?", data.damage);
         debug!("layout: parsed Node tree");
         debug!("%?", node.dump());
 
@@ -176,9 +195,15 @@ impl Layout {
             node.initialize_style_for_subtree(&self.layout_refs);
         }
 
-        do time("layout: selector matching") {
-            do self.css_select_ctx.borrow_imm |ctx| {
-                node.restyle_subtree(ctx);
+        // Perform CSS selector matching if necessary.
+        match data.damage {
+            NoDamage | ReflowDamage => {}
+            MatchSelectorsDamage => {
+                do time("layout: selector matching") {
+                    do self.css_select_ctx.borrow_imm |ctx| {
+                        node.restyle_subtree(ctx);
+                    }
+                }
             }
         }