Merge pull request #2788 from mrobinson/compositor-cleanup

Make compositor layer creation atomic

4 files changed, 152 insertions, 260 deletions

diff --git a/src/components/compositing/compositor.rs b/src/components/compositing/compositor.rs
index f92a2920531..bd76573a0b0 100644
--- a/src/components/compositing/compositor.rs
+++ b/src/components/compositing/compositor.rs
@@ -3,9 +3,8 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use compositor_data::CompositorData;
-use compositor_task::{Msg, CompositorTask, Exit, ChangeReadyState, SetUnRenderedColor};
-use compositor_task::{SetIds, GetGraphicsMetadata, CreateRootCompositorLayerIfNecessary};
-use compositor_task::{CreateDescendantCompositorLayerIfNecessary, SetLayerPageSize};
+use compositor_task::{Msg, CompositorTask, Exit, ChangeReadyState, SetIds, LayerProperties};
+use compositor_task::{GetGraphicsMetadata, CreateOrUpdateRootLayer, CreateOrUpdateDescendantLayer};
 use compositor_task::{SetLayerClipRect, Paint, ScrollFragmentPoint, LoadComplete};
 use compositor_task::{ShutdownComplete, ChangeRenderState};
 use constellation::SendableFrameTree;
@@ -19,12 +18,12 @@ use windowing::{QuitWindowEvent, RefreshWindowEvent, ResizeWindowEvent, ScrollWi
 use windowing::{WindowEvent, WindowMethods, WindowNavigateMsg, ZoomWindowEvent};
 use windowing::PinchZoomWindowEvent;
 
-use azure::azure_hl::{SourceSurfaceMethods, Color};
+use azure::azure_hl::SourceSurfaceMethods;
 use azure::azure_hl;
 use geom::matrix::identity;
 use geom::point::{Point2D, TypedPoint2D};
 use geom::rect::Rect;
-use geom::size::{Size2D, TypedSize2D};
+use geom::size::TypedSize2D;
 use geom::scale_factor::ScaleFactor;
 use layers::layers::LayerBufferSet;
 use layers::platform::surface::NativeCompositingGraphicsContext;
@@ -35,7 +34,7 @@ use layers::layers::Layer;
 use opengles::gl2;
 use png;
 use servo_msg::compositor_msg::{Blank, Epoch, FinishedLoading, IdleRenderState};
-use servo_msg::compositor_msg::{LayerId, ReadyState, RenderState, ScrollPolicy, Scrollable};
+use servo_msg::compositor_msg::{LayerId, ReadyState, RenderState};
 use servo_msg::constellation_msg::{ConstellationChan, ExitMsg, LoadUrlMsg, NavigateMsg};
 use servo_msg::constellation_msg::{PipelineId, ResizedWindowMsg, WindowSizeData};
 use servo_msg::constellation_msg;
@@ -279,10 +278,6 @@ impl IOCompositor {
                     self.change_render_state(render_state);
                 }
 
-                (Ok(SetUnRenderedColor(pipeline_id, layer_id, color)), NotShuttingDown) => {
-                    self.set_unrendered_color(pipeline_id, layer_id, color);
-                }
-
                 (Ok(SetIds(frame_tree, response_chan, new_constellation_chan)), _) => {
                     self.set_ids(frame_tree, response_chan, new_constellation_chan);
                 }
@@ -291,27 +286,14 @@ impl IOCompositor {
                     chan.send(Some(azure_hl::current_graphics_metadata()));
                 }
 
-                (Ok(CreateRootCompositorLayerIfNecessary(pipeline_id, layer_id, size, color)),
+                (Ok(CreateOrUpdateRootLayer(layer_properties)),
                  NotShuttingDown) => {
-                    self.create_root_compositor_layer_if_necessary(pipeline_id,
-                                                                   layer_id,
-                                                                   size,
-                                                                   color);
+                    self.create_or_update_root_layer(layer_properties);
                 }
 
-                (Ok(CreateDescendantCompositorLayerIfNecessary(pipeline_id,
-                                                                 layer_id,
-                                                                 rect,
-                                                                 scroll_behavior)),
+                (Ok(CreateOrUpdateDescendantLayer(layer_properties)),
                  NotShuttingDown) => {
-                    self.create_descendant_compositor_layer_if_necessary(pipeline_id,
-                                                                         layer_id,
-                                                                         rect,
-                                                                         scroll_behavior);
-                }
-
-                (Ok(SetLayerPageSize(pipeline_id, layer_id, new_size, epoch)), NotShuttingDown) => {
-                    self.set_layer_page_size(pipeline_id, layer_id, new_size, epoch);
+                    self.create_or_update_descendant_layer(layer_properties);
                 }
 
                 (Ok(SetLayerClipRect(pipeline_id, layer_id, new_rect)), NotShuttingDown) => {
@@ -346,20 +328,6 @@ impl IOCompositor {
         }
     }
 
-    fn set_unrendered_color(&mut self, pipeline_id: PipelineId, layer_id: LayerId, color: Color) {
-        match self.scene.root {
-            Some(ref root_layer) => {
-                match CompositorData::find_layer_with_pipeline_and_layer_id(root_layer.clone(),
-                                                                            pipeline_id,
-                                                                            layer_id) {
-                    Some(ref layer) => CompositorData::set_unrendered_color(layer.clone(), color),
-                    None => { }
-                }
-            }
-            None => { }
-        }
-    }
-
     fn set_ids(&mut self,
                frame_tree: SendableFrameTree,
                response_chan: Sender<()>,
@@ -373,40 +341,41 @@ impl IOCompositor {
         self.send_window_size();
     }
 
-    fn create_root_compositor_layer_if_necessary(&mut self,
-                                                 id: PipelineId,
-                                                 layer_id: LayerId,
-                                                 size: Size2D<f32>,
-                                                 unrendered_color: Color) {
-        let (root_pipeline, root_layer_id) = match self.scene.root {
-            Some(ref root_layer) if root_layer.extra_data.borrow().pipeline.id == id => {
-                (root_layer.extra_data.borrow().pipeline.clone(),
-                 CompositorData::id_of_first_child(root_layer.clone()))
-            }
-            _ => {
-                match self.root_pipeline {
-                    Some(ref root_pipeline) => {
-                        (root_pipeline.clone(), LayerId::null())
-                    },
-                    _ => fail!("Compositor: Received new layer without initialized pipeline"),
-                }
+    fn update_layer_if_exists(&mut self, properties: LayerProperties) -> bool {
+        match self.scene.root {
+            Some(ref root_layer) => {
+                match CompositorData::find_layer_with_pipeline_and_layer_id(root_layer.clone(),
+                                                                            properties.pipeline_id,
+                                                                            properties.id) {
+                    Some(existing_layer) => {
+                        CompositorData::update_layer(existing_layer.clone(), properties);
+                        true
+                    }
+                    None => false,
+               }
             }
-        };
+            None => false,
+        }
+    }
 
-        if layer_id != root_layer_id {
+    fn create_or_update_root_layer(&mut self, layer_properties: LayerProperties) {
+        let need_new_root_layer = !self.update_layer_if_exists(layer_properties);
+        if need_new_root_layer {
+            let root_pipeline = match self.root_pipeline {
+                Some(ref root_pipeline) => root_pipeline.clone(),
+                None => fail!("Compositor: Making new layer without initialized pipeline"),
+            };
             let new_compositor_data = CompositorData::new_root(root_pipeline,
-                                                               size,
-                                                               self.opts.cpu_painting);
+                                                               layer_properties.epoch,
+                                                               layer_properties.rect.size,
+                                                               self.opts.cpu_painting,
+                                                               layer_properties.background_color);
+            let size = layer_properties.rect.size;
             let new_root = Rc::new(Layer::new(size,
                                               self.opts.tile_size,
                                               new_compositor_data));
-            new_root.extra_data.borrow_mut().unrendered_color = unrendered_color;
 
-            CompositorData::add_child_if_necessary(new_root.clone(),
-                                                   layer_id,
-                                                   Rect(Point2D(0f32, 0f32), size),
-                                                   size,
-                                                   Scrollable);
+            CompositorData::add_child(new_root.clone(), layer_properties, size);
 
             // Release all tiles from the layer before dropping it.
             match self.scene.root {
@@ -416,27 +385,30 @@ impl IOCompositor {
             self.scene.root = Some(new_root);
         }
 
+        self.scroll_layer_to_fragment_point_if_necessary(layer_properties.pipeline_id,
+                                                         layer_properties.id);
+        self.ask_for_tiles();
+    }
+
+    fn create_or_update_descendant_layer(&mut self, layer_properties: LayerProperties) {
+        if !self.update_layer_if_exists(layer_properties) {
+            self.create_descendant_layer(layer_properties);
+        }
+        self.scroll_layer_to_fragment_point_if_necessary(layer_properties.pipeline_id,
+                                                         layer_properties.id);
         self.ask_for_tiles();
     }
 
-    fn create_descendant_compositor_layer_if_necessary(&mut self,
-                                                       pipeline_id: PipelineId,
-                                                       layer_id: LayerId,
-                                                       rect: Rect<f32>,
-                                                       scroll_policy: ScrollPolicy) {
+    fn create_descendant_layer(&self, layer_properties: LayerProperties) {
         match self.scene.root {
             Some(ref root_layer) => {
                 let parent_layer_id = root_layer.extra_data.borrow().id;
                 match CompositorData::find_layer_with_pipeline_and_layer_id(root_layer.clone(),
-                                                                            pipeline_id,
+                                                                            layer_properties.pipeline_id,
                                                                             parent_layer_id) {
                     Some(ref mut parent_layer) => {
                         let page_size = root_layer.extra_data.borrow().page_size.unwrap();
-                        CompositorData::add_child_if_necessary(parent_layer.clone(),
-                                                               layer_id,
-                                                               rect,
-                                                               page_size,
-                                                               scroll_policy);
+                        CompositorData::add_child(parent_layer.clone(), layer_properties, page_size);
                     }
                     None => {
                         fail!("Compositor: couldn't find parent layer");
@@ -445,8 +417,6 @@ impl IOCompositor {
             }
             None => fail!("Compositor: Received new layer without initialized pipeline")
         }
-
-        self.ask_for_tiles();
     }
 
     /// The size of the content area in CSS px at the current zoom level
@@ -467,33 +437,24 @@ impl IOCompositor {
         }));
     }
 
-    fn set_layer_page_size(&mut self,
-                           pipeline_id: PipelineId,
-                           layer_id: LayerId,
-                           new_size: Size2D<f32>,
-                           epoch: Epoch) {
+    fn scroll_layer_to_fragment_point_if_necessary(&mut self,
+                                                   pipeline_id: PipelineId,
+                                                   layer_id: LayerId) {
         let page_window = self.page_window();
-        let (ask, move): (bool, bool) = match self.scene.root {
-            Some(ref layer) => {
-                CompositorData::resize(layer.clone(),
-                                       pipeline_id,
-                                       layer_id,
-                                       new_size,
-                                       page_window,
-                                       epoch);
-                let move = self.fragment_point.take().map_or(false, |point| {
-                    CompositorData::move(layer.clone(), pipeline_id, layer_id, point, page_window)
-                });
-
-                (true, move)
-            }
-            None => (false, false)
+        let needs_recomposite = match self.scene.root {
+            Some(ref mut root_layer) => {
+                self.fragment_point.take().map_or(false, |fragment_point| {
+                    CompositorData::move(root_layer.clone(),
+                                         pipeline_id,
+                                         layer_id,
+                                         fragment_point,
+                                         page_window)
+                })
+            }
+            None => fail!("Compositor: Tried to scroll to fragment without root layer."),
         };
 
-        if ask {
-            self.recomposite_if(move);
-            self.ask_for_tiles();
-        }
+        self.recomposite_if(needs_recomposite);
     }
 
     fn set_layer_clip_rect(&mut self,
diff --git a/src/components/compositing/compositor_data.rs b/src/components/compositing/compositor_data.rs
index 86d4fa2aeb0..af845f5312a 100644
--- a/src/components/compositing/compositor_data.rs
+++ b/src/components/compositing/compositor_data.rs
@@ -2,6 +2,7 @@
  * 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/. */
 
+use compositor_task::LayerProperties;
 use pipeline::CompositionPipeline;
 use windowing::{MouseWindowEvent, MouseWindowClickEvent, MouseWindowMouseDownEvent};
 use windowing::{MouseWindowMouseUpEvent};
@@ -13,7 +14,6 @@ use geom::point::{Point2D, TypedPoint2D};
 use geom::rect::{Rect, TypedRect};
 use geom::size::{Size2D, TypedSize2D};
 use gfx::render_task::{ReRenderMsg, UnusedBufferMsg};
-use gfx;
 use layers::layers::{Layer, Flip, LayerBuffer, LayerBufferSet, NoFlip, TextureLayer};
 use layers::quadtree::{Tile, Normal, Hidden};
 use layers::platform::surface::{NativeCompositingGraphicsContext, NativeSurfaceMethods};
@@ -103,77 +103,67 @@ impl Clampable for f32 {
 impl CompositorData {
     pub fn new(pipeline: CompositionPipeline,
                layer_id: LayerId,
+               epoch: Epoch,
                bounds: Rect<f32>,
                page_size: Option<Size2D<f32>>,
                cpu_painting: bool,
                wants_scroll_events: WantsScrollEventsFlag,
                scroll_policy: ScrollPolicy,
-               hidden: bool) -> CompositorData {
+               unrendered_color: Color)
+               -> CompositorData {
         CompositorData {
             pipeline: pipeline,
             id: layer_id,
             scroll_offset: TypedPoint2D(0f32, 0f32),
             bounds: bounds,
             page_size: page_size,
-            hidden: hidden,
+            hidden: false,
             wants_scroll_events: wants_scroll_events,
             scroll_policy: scroll_policy,
             cpu_painting: cpu_painting,
-            unrendered_color: gfx::color::rgba(0.0, 0.0, 0.0, 0.0),
+            unrendered_color: unrendered_color,
             scissor: None,
-            epoch: Epoch(0),
+            epoch: epoch,
         }
     }
 
     pub fn new_root(pipeline: CompositionPipeline,
+                    epoch: Epoch,
                     page_size: Size2D<f32>,
-                    cpu_painting: bool) -> CompositorData {
+                    cpu_painting: bool,
+                    unrendered_color: Color) -> CompositorData {
         CompositorData::new(pipeline,
                             LayerId::null(),
+                            epoch,
                             Rect(Point2D(0f32, 0f32), page_size),
                             Some(page_size),
                             cpu_painting,
                             WantsScrollEvents,
                             FixedPosition,
-                            false)
-    }
-
-
-    pub fn id_of_first_child(layer: Rc<Layer<CompositorData>>) -> LayerId {
-        layer.children().iter().next().expect("no first child!").extra_data.borrow().id
+                            unrendered_color)
     }
 
     /// Adds a child layer to the layer with the given ID and the given pipeline, if it doesn't
     /// exist yet. The child layer will have the same pipeline, tile size, memory limit, and CPU
     /// painting status as its parent.
-    pub fn add_child_if_necessary(layer: Rc<Layer<CompositorData>>,
-                                  child_layer_id: LayerId,
-                                  rect: Rect<f32>,
-                                  page_size: Size2D<f32>,
-                                  scroll_policy: ScrollPolicy) {
-        // See if we've already made this child layer.
-        let pipeline_id = layer.extra_data.borrow().pipeline.id;
-        if layer.children().iter().any(|kid| {
-                    kid.extra_data.borrow().pipeline.id == pipeline_id &&
-                    kid.extra_data.borrow().id == child_layer_id
-                }) {
-            return;
-        }
-
+    pub fn add_child(layer: Rc<Layer<CompositorData>>,
+                     layer_properties: LayerProperties,
+                     page_size: Size2D<f32>) {
         let new_compositor_data = CompositorData::new(layer.extra_data.borrow().pipeline.clone(),
-                                                      child_layer_id,
-                                                      rect,
+                                                      layer_properties.id,
+                                                      layer_properties.epoch,
+                                                      layer_properties.rect,
                                                       Some(page_size),
                                                       layer.extra_data.borrow().cpu_painting,
                                                       DoesntWantScrollEvents,
-                                                      scroll_policy,
-                                                      false);
+                                                      layer_properties.scroll_policy,
+                                                      layer_properties.background_color);
         let new_kid = Rc::new(Layer::new(page_size,
                                          Layer::tile_size(layer.clone()),
                                          new_compositor_data));
 
-        new_kid.extra_data.borrow_mut().scissor = Some(rect);
-        *new_kid.origin.borrow_mut() = rect.origin;
+        new_kid.extra_data.borrow_mut().scissor = Some(layer_properties.rect);
+        *new_kid.origin.borrow_mut() = layer_properties.rect.origin;
 
         // Place the kid's layer in the container passed in.
         Layer::add_child(layer.clone(), new_kid.clone());
@@ -423,46 +413,42 @@ impl CompositorData {
         }
     }
 
-    // Set the layer's page size. This signals that the renderer is ready for BufferRequests.
-    // If the layer is hidden and has a defined clipping rect, unhide it.
-    // This method returns false if the specified layer is not found.
-    pub fn resize(layer: Rc<Layer<CompositorData>>,
-                  pipeline_id: PipelineId,
-                  layer_id: LayerId,
-                  new_size: Size2D<f32>,
-                  window_size: TypedSize2D<PagePx, f32>,
-                  epoch: Epoch)
-                  -> bool {
-        debug!("compositor_data: starting resize()");
-        if layer.extra_data.borrow().pipeline.id != pipeline_id ||
-           layer.extra_data.borrow().id != layer_id {
-            return CompositorData::resize_helper(layer.clone(),
-                                                 pipeline_id,
-                                                 layer_id,
-                                                 new_size,
-                                                 epoch)
-        }
+    pub fn update_layer(layer: Rc<Layer<CompositorData>>, layer_properties: LayerProperties) {
+        layer.extra_data.borrow_mut().epoch = layer_properties.epoch;
+        layer.extra_data.borrow_mut().unrendered_color = layer_properties.background_color;
+        CompositorData::resize(layer.clone(), layer_properties.rect.size);
+    }
+
+    // Resize and unhide a pre-existing layer. A new layer's size is set during creation.
+    fn resize(layer: Rc<Layer<CompositorData>>,
+              new_size: Size2D<f32>) {
+        debug!("compositor_data: starting resize_helper()");
 
-        debug!("compositor_data: layer found for resize()");
-        layer.extra_data.borrow_mut().epoch = epoch;
+        debug!("compositor_data: layer found for resize_helper()");
         layer.extra_data.borrow_mut().page_size = Some(new_size);
 
         let unused_buffers = Layer::resize(layer.clone(), new_size);
         if !unused_buffers.is_empty() {
-            let _ = layer.extra_data.borrow().pipeline
-                    .render_chan
-                    .send_opt(UnusedBufferMsg(unused_buffers));
+            let msg = UnusedBufferMsg(unused_buffers);
+            let _ = layer.extra_data.borrow().pipeline.render_chan.send_opt(msg);
+        }
+
+        let scissor_clone = layer.extra_data.borrow().scissor.clone();
+        match scissor_clone {
+            Some(scissor) => {
+                // Call scroll for bounds checking if the page shrunk. Use (-1, -1) as the
+                // cursor position to make sure the scroll isn't propagated downwards.
+                let size: TypedSize2D<PagePx, f32> = Size2D::from_untyped(&scissor.size);
+                CompositorData::handle_scroll_event(layer.clone(),
+                                                    TypedPoint2D(0f32, 0f32),
+                                                    TypedPoint2D(-1f32, -1f32),
+                                                    size);
+                layer.extra_data.borrow_mut().hidden = false;
+            }
+            None => {} // Nothing to do
         }
 
-        // Call scroll for bounds checking if the page shrunk. Use (-1, -1) as the cursor position
-        // to make sure the scroll isn't propagated downwards.
-        CompositorData::handle_scroll_event(layer.clone(),
-                                            TypedPoint2D(0f32, 0f32),
-                                            TypedPoint2D(-1f32, -1f32),
-                                            window_size);
-        layer.extra_data.borrow_mut().hidden = false;
         CompositorData::set_occlusions(layer.clone());
-        true
     }
 
     pub fn move(layer: Rc<Layer<CompositorData>>,
@@ -537,8 +523,6 @@ impl CompositorData {
         (NoFlip, TextureTarget2D)
     }
 
-
-
     fn find_child_with_pipeline_and_layer_id(layer: Rc<Layer<CompositorData>>,
                                              pipeline_id: PipelineId,
                                              layer_id: LayerId)
@@ -573,60 +557,6 @@ impl CompositorData {
         return None;
     }
 
-    // A helper method to resize sublayers.
-    fn resize_helper(layer: Rc<Layer<CompositorData>>,
-                     pipeline_id: PipelineId,
-                     layer_id: LayerId,
-                     new_size: Size2D<f32>,
-                     epoch: Epoch)
-                     -> bool {
-        debug!("compositor_data: starting resize_helper()");
-
-        let found = match CompositorData::find_child_with_pipeline_and_layer_id(layer.clone(),
-                                                                                pipeline_id,
-                                                                                layer_id) {
-            Some(child) => {
-                debug!("compositor_data: layer found for resize_helper()");
-                child.extra_data.borrow_mut().epoch = epoch;
-                child.extra_data.borrow_mut().page_size = Some(new_size);
-
-                let unused_buffers = Layer::resize(child.clone(), new_size);
-                if !unused_buffers.is_empty() {
-                    let msg = UnusedBufferMsg(unused_buffers);
-                    let _ = child.extra_data.borrow().pipeline.render_chan.send_opt(msg);
-                }
-
-                let scissor_clone = child.extra_data.borrow().scissor.clone();
-                match scissor_clone {
-                    Some(scissor) => {
-                        // Call scroll for bounds checking if the page shrunk. Use (-1, -1) as the
-                        // cursor position to make sure the scroll isn't propagated downwards.
-                        let size: TypedSize2D<PagePx, f32> = Size2D::from_untyped(&scissor.size);
-                        CompositorData::handle_scroll_event(child.clone(),
-                                                            TypedPoint2D(0f32, 0f32),
-                                                            TypedPoint2D(-1f32, -1f32),
-                                                            size);
-                        child.extra_data.borrow_mut().hidden = false;
-                    }
-                    None => {} // Nothing to do
-                }
-                true
-            }
-            None => false,
-        };
-
-        if found { // Boolean flag to get around double borrow of self
-            CompositorData::set_occlusions(layer.clone());
-            return true
-        }
-
-        // If we got here, the layer's ID does not match ours, so recurse on descendents (including
-        // hidden children).
-        layer.children().iter().any(|kid| {
-            CompositorData::resize_helper(kid.clone(), pipeline_id, layer_id, new_size, epoch)
-        })
-    }
-
     // Collect buffers from the quadtree. This method IS NOT recursive, so child layers
     // are not rebuilt directly from this method.
     pub fn build_layer_tree(layer: Rc<Layer<CompositorData>>,
@@ -766,9 +696,5 @@ impl CompositorData {
             CompositorData::forget_all_tiles(kid.clone());
         }
     }
-
-    pub fn set_unrendered_color(layer: Rc<Layer<CompositorData>>, color: Color) {
-        layer.extra_data.borrow_mut().unrendered_color = color;
-    }
 }
 
diff --git a/src/components/compositing/compositor_task.rs b/src/components/compositing/compositor_task.rs
index 1b8e9653744..7534131a935 100644
--- a/src/components/compositing/compositor_task.rs
+++ b/src/components/compositing/compositor_task.rs
@@ -61,6 +61,31 @@ impl ScriptListener for CompositorChan {
     }
 }
 
+pub struct LayerProperties {
+    pub pipeline_id: PipelineId,
+    pub epoch: Epoch,
+    pub id: LayerId,
+    pub rect: Rect<f32>,
+    pub background_color: Color,
+    pub scroll_policy: ScrollPolicy,
+}
+
+impl LayerProperties {
+    fn new(pipeline_id: PipelineId, epoch: Epoch, metadata: &LayerMetadata) -> LayerProperties {
+        LayerProperties {
+            pipeline_id: pipeline_id,
+            epoch: epoch,
+            id: metadata.id,
+            rect: Rect(Point2D(metadata.position.origin.x as f32,
+                               metadata.position.origin.y as f32),
+                       Size2D(metadata.position.size.width as f32,
+                              metadata.position.size.height as f32)),
+           background_color: metadata.background_color,
+           scroll_policy: metadata.scroll_policy,
+        }
+    }
+}
+
 /// Implementation of the abstract `RenderListener` interface.
 impl RenderListener for CompositorChan {
     fn get_graphics_metadata(&self) -> Option<NativeGraphicsMetadata> {
@@ -86,30 +111,15 @@ impl RenderListener for CompositorChan {
         // `position: fixed` but will not be sufficient to handle `overflow: scroll` or transforms.
         let mut first = true;
         for metadata in metadata.iter() {
-            let origin = Point2D(metadata.position.origin.x as f32,
-                                 metadata.position.origin.y as f32);
-            let size = Size2D(metadata.position.size.width as f32,
-                              metadata.position.size.height as f32);
-            let rect = Rect(origin, size);
+            let layer_properties = LayerProperties::new(pipeline_id, epoch, metadata);
             if first {
-                self.chan.send(CreateRootCompositorLayerIfNecessary(pipeline_id,
-                                                                    metadata.id,
-                                                                    size,
-                                                                    metadata.background_color));
+                self.chan.send(CreateOrUpdateRootLayer(layer_properties));
                 first = false
             } else {
-                self.chan
-                    .send(CreateDescendantCompositorLayerIfNecessary(pipeline_id,
-                                                                     metadata.id,
-                                                                     rect,
-                                                                     metadata.scroll_policy));
+                self.chan.send(CreateOrUpdateDescendantLayer(layer_properties));
             }
 
-            self.chan.send(SetUnRenderedColor(pipeline_id,
-                                              metadata.id,
-                                              metadata.background_color));
-            self.chan.send(SetLayerPageSize(pipeline_id, metadata.id, size, epoch));
-            self.chan.send(SetLayerClipRect(pipeline_id, metadata.id, rect));
+            self.chan.send(SetLayerClipRect(pipeline_id, metadata.id, layer_properties.rect));
         }
     }
 
@@ -161,12 +171,10 @@ pub enum Msg {
 
     /// Tells the compositor to create the root layer for a pipeline if necessary (i.e. if no layer
     /// with that ID exists).
-    CreateRootCompositorLayerIfNecessary(PipelineId, LayerId, Size2D<f32>, Color),
+    CreateOrUpdateRootLayer(LayerProperties),
     /// Tells the compositor to create a descendant layer for a pipeline if necessary (i.e. if no
     /// layer with that ID exists).
-    CreateDescendantCompositorLayerIfNecessary(PipelineId, LayerId, Rect<f32>, ScrollPolicy),
-    /// Alerts the compositor that the specified layer has changed size.
-    SetLayerPageSize(PipelineId, LayerId, Size2D<f32>, Epoch),
+    CreateOrUpdateDescendantLayer(LayerProperties),
     /// Alerts the compositor that the specified layer's clipping rect has changed.
     SetLayerClipRect(PipelineId, LayerId, Rect<f32>),
     /// Scroll a page in a window
@@ -179,8 +187,6 @@ pub enum Msg {
     ChangeRenderState(RenderState),
     /// Sets the channel to the current layout and render tasks, along with their id
     SetIds(SendableFrameTree, Sender<()>, ConstellationChan),
-    /// Sets the color of unrendered content for a layer.
-    SetUnRenderedColor(PipelineId, LayerId, Color),
     /// The load of a page for a given URL has completed.
     LoadComplete(PipelineId, Url),
 }
diff --git a/src/components/compositing/headless.rs b/src/components/compositing/headless.rs
index c588b57cfad..a76cbfa9905 100644
--- a/src/components/compositing/headless.rs
+++ b/src/components/compositing/headless.rs
@@ -2,9 +2,8 @@
  * 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/. */
 
-use compositor_task::{Msg, Exit, ChangeReadyState, SetUnRenderedColor};
-use compositor_task::{SetIds, GetGraphicsMetadata, CreateRootCompositorLayerIfNecessary};
-use compositor_task::{CreateDescendantCompositorLayerIfNecessary, SetLayerPageSize};
+use compositor_task::{Msg, Exit, ChangeReadyState, SetIds};
+use compositor_task::{GetGraphicsMetadata, CreateOrUpdateRootLayer, CreateOrUpdateDescendantLayer};
 use compositor_task::{SetLayerClipRect, Paint, ScrollFragmentPoint, LoadComplete};
 use compositor_task::{ShutdownComplete, ChangeRenderState};
 
@@ -89,11 +88,11 @@ impl NullCompositor {
                 // we'll notice and think about whether it needs a response, like
                 // SetIds.
 
-                CreateRootCompositorLayerIfNecessary(..) |
-                CreateDescendantCompositorLayerIfNecessary(..) | SetLayerPageSize(..) |
+                CreateOrUpdateRootLayer(..) |
+                CreateOrUpdateDescendantLayer(..) |
                 SetLayerClipRect(..) | Paint(..) |
                 ChangeReadyState(..) | ChangeRenderState(..) | ScrollFragmentPoint(..) |
-                SetUnRenderedColor(..) | LoadComplete(..) => ()
+                LoadComplete(..) => ()
             }
         }
     }