Stop rendering when script queries layout

src/components/main/layout/layout_task.rs

@@ -36,7 +36,7 @@ use script::layout_interface::{AddStylesheetMsg, BuildData, BuildMsg, ContentBox
 use script::layout_interface::{HitTestQuery, ContentBoxResponse, HitTestResponse};
 use script::layout_interface::{ContentBoxesQuery, ContentBoxesResponse, ExitMsg, LayoutQuery};
 use script::layout_interface::{LayoutResponse, LayoutTask, MatchSelectorsDamage, Msg, NoDamage};
-use script::layout_interface::{QueryMsg, ReflowDamage};
+use script::layout_interface::{QueryMsg, ReflowDamage, ReflowForDisplay};
 use script::script_task::{ScriptMsg, SendEventMsg};
 use servo_net::image_cache_task::{ImageCacheTask, ImageResponseMsg};
 use servo_net::local_image_cache::LocalImageCache;
@@ -227,29 +227,31 @@ impl Layout {
             };
         }
 
-        // Build the display list, and send it to the renderer.
-        do profile(time::LayoutDispListBuildCategory, self.profiler_chan.clone()) {
-            let builder = DisplayListBuilder {
-                ctx: &layout_ctx,
-            };
+        // Build the display list if necessary, and send it to the renderer.
+        if data.goal == ReflowForDisplay {
+            do profile(time::LayoutDispListBuildCategory, self.profiler_chan.clone()) {
+                let builder = DisplayListBuilder {
+                    ctx: &layout_ctx,
+                };
 
-            let display_list = @Cell(DisplayList::new());
-            
-            // TODO: Set options on the builder before building.
-            // TODO: Be smarter about what needs painting.
-            layout_root.build_display_list(&builder, &layout_root.position(), display_list);
+                let display_list = @Cell(DisplayList::new());
 
-            let root_size = do layout_root.with_base |base| {
-                base.position.size
-            };
+                // TODO: Set options on the builder before building.
+                // TODO: Be smarter about what needs painting.
+                layout_root.build_display_list(&builder, &layout_root.position(), display_list);
 
-            let render_layer = RenderLayer {
-                display_list: display_list.take(),
-                size: Size2D(root_size.width.to_px() as uint, root_size.height.to_px() as uint)
-            };
+                let root_size = do layout_root.with_base |base| {
+                    base.position.size
+                };
 
-            self.render_task.channel.send(RenderMsg(render_layer));
-        } // time(layout: display list building)
+                let render_layer = RenderLayer {
+                    display_list: display_list.take(),
+                    size: Size2D(root_size.width.to_px() as uint, root_size.height.to_px() as uint)
+                };
+
+                self.render_task.channel.send(RenderMsg(render_layer));
+            } // time(layout: display list building)
+        }
 
         // Tell script that we're done.
         data.script_join_chan.send(());

src/components/script/layout_interface.rs

@@ -86,11 +86,22 @@ impl Damage {
     }
 }
 
+/// Why we're doing reflow.
+#[deriving(Eq)]
+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 BuildData {
     node: AbstractNode<ScriptView>,
     /// What reflow needs to be done.
     damage: Damage,
+    /// The goal of reflow: either to render to the screen or to flush layout info for script.
+    goal: ReflowGoal,
     /// The URL of the page.
     url: Url,
     /// The channel through which messages can be sent back to the script task.

src/components/script/script_task.rs

@@ -12,7 +12,7 @@ use dom::node::define_bindings;
 use dom::window::Window;
 use layout_interface::{AddStylesheetMsg, BuildData, BuildMsg, Damage, LayoutQuery, HitTestQuery};
 use layout_interface::{LayoutResponse, HitTestResponse, LayoutTask, MatchSelectorsDamage, NoDamage};
-use layout_interface::{QueryMsg, ReflowDamage};
+use layout_interface::{QueryMsg, ReflowDamage, ReflowForDisplay, ReflowForScriptQuery, ReflowGoal};
 use layout_interface;
 
 use core::cast::transmute;
@@ -283,7 +283,7 @@ impl ScriptContext {
                              null(),
                              &rval);
 
-        self.relayout()
+        self.relayout(ReflowForScriptQuery)
     }
 
     /// Handles a request to exit the script task and shut down layout.
@@ -349,7 +349,7 @@ impl ScriptContext {
 
         // Perform the initial reflow.
         self.damage.add(MatchSelectorsDamage);
-        self.relayout();
+        self.relayout(ReflowForDisplay);
 
         // Define debug functions.
         self.js_compartment.define_functions(debug_fns);
@@ -383,10 +383,10 @@ impl ScriptContext {
         }
     }
 
-    /// Initiate an asynchronous relayout operation
+    /// Initiate an asynchronous relayout operation to handle a script layout query.
     pub fn trigger_relayout(&mut self, damage: Damage) {
         self.damage.add(damage);
-        self.relayout();
+        self.relayout(ReflowForScriptQuery);
     }
 
     /// This method will wait until the layout task has completed its current action, join the
@@ -394,7 +394,7 @@ impl ScriptContext {
     /// computation to finish.
     ///
     /// This function fails if there is no root frame.
-    fn relayout(&mut self) {
+    fn relayout(&mut self, goal: ReflowGoal) {
         debug!("script: performing relayout");
 
         // Now, join the layout so that they will see the latest changes we have made.
@@ -411,6 +411,7 @@ impl ScriptContext {
                 let data = ~BuildData {
                     node: root_frame.document.root,
                     url: copy root_frame.url,
+                    goal: goal,
                     script_chan: self.script_chan.clone(),
                     window_size: self.window_size,
                     script_join_chan: join_chan,
@@ -445,7 +446,7 @@ impl ScriptContext {
                 self.window_size = Size2D(new_width, new_height);
 
                 if self.root_frame.is_some() {
-                    self.relayout()
+                    self.relayout(ReflowForDisplay)
                 }
 
                 response_chan.send(())
@@ -457,7 +458,7 @@ impl ScriptContext {
                 self.damage.add(MatchSelectorsDamage);
 
                 if self.root_frame.is_some() {
-                    self.relayout()
+                    self.relayout(ReflowForDisplay)
                 }
             }