pipe through a scene_id to distinguish cached pictures

webrender/src/display_list_flattener.rs

@@ -204,6 +204,7 @@ impl<'a> DisplayListFlattener<'a> {
         output_pipelines: &FastHashSet<PipelineId>,
         frame_builder_config: &FrameBuilderConfig,
         new_scene: &mut Scene,
+        scene_id: u64,
     ) -> FrameBuilder {
         // We checked that the root pipeline is available on the render backend.
         let root_pipeline_id = scene.root_pipeline_id.unwrap();
@@ -254,7 +255,8 @@ impl<'a> DisplayListFlattener<'a> {
             view.inner_rect,
             background_color,
             view.window_size,
-            flattener
+            scene_id,
+            flattener,
         )
     }
 
@@ -2062,7 +2064,8 @@ pub fn build_scene(config: &FrameBuilderConfig, request: SceneRequest) -> BuiltS
         &request.view,
         &request.output_pipelines,
         config,
-        &mut new_scene
+        &mut new_scene,
+        request.scene_id,
     );
 
     BuiltScene {

webrender/src/frame_builder.rs

@@ -41,6 +41,7 @@ pub struct FrameBuilder {
     screen_rect: DeviceUintRect,
     background_color: Option<ColorF>,
     window_size: DeviceUintSize,
+    scene_id: u64,
     pub prim_store: PrimitiveStore,
     pub clip_store: ClipStore,
     pub hit_testing_runs: Vec<HitTestingRun>,
@@ -50,6 +51,7 @@ pub struct FrameBuilder {
 }
 
 pub struct FrameBuildingContext<'a> {
+    pub scene_id: u64,
     pub device_pixel_scale: DevicePixelScale,
     pub scene_properties: &'a SceneProperties,
     pub pipelines: &'a FastHashMap<PipelineId, Arc<ScenePipeline>>,
@@ -125,6 +127,7 @@ impl FrameBuilder {
             screen_rect: DeviceUintRect::zero(),
             window_size: DeviceUintSize::zero(),
             background_color: None,
+            scene_id: 0,
             config: FrameBuilderConfig {
                 enable_scrollbars: false,
                 default_font_render_mode: FontRenderMode::Mono,
@@ -138,6 +141,7 @@ impl FrameBuilder {
         screen_rect: DeviceUintRect,
         background_color: Option<ColorF>,
         window_size: DeviceUintSize,
+        scene_id: u64,
         flattener: DisplayListFlattener,
     ) -> Self {
         FrameBuilder {
@@ -149,6 +153,7 @@ impl FrameBuilder {
             screen_rect,
             background_color,
             window_size,
+            scene_id,
             config: flattener.config,
         }
     }
@@ -185,6 +190,7 @@ impl FrameBuilder {
             .display_list;
 
         let frame_context = FrameBuildingContext {
+            scene_id: self.scene_id,
             device_pixel_scale,
             scene_properties,
             pipelines,

webrender/src/picture.rs

@@ -80,7 +80,11 @@ pub struct PictureCacheKey {
     //       we relax that, we'll need to consider some
     //       extra parameters, depending on transform.
 
-    // The unique identifier for this picture.
+    // This is a globally unique id of the scene this picture 
+    // is associated with, to avoid picture id collisions.
+    scene_id: u64,
+
+    // The unique (for the scene_id) identifier for this picture.
     // TODO(gw): Currently, these will not be
     //           shared across new display lists,
     //           so will only remain valid during
@@ -374,6 +378,7 @@ impl PicturePrimitive {
                         RenderTaskCacheKey {
                             size: device_rect.size,
                             kind: RenderTaskCacheKeyKind::Picture(PictureCacheKey {
+                                scene_id: frame_context.scene_id,
                                 picture_id: self.id,
                                 unclipped_size: prim_screen_rect.unclipped.size,
                                 pic_relative_render_rect,

webrender/src/render_backend.rs

@@ -176,7 +176,7 @@ impl Document {
     }
 
     // TODO: We will probably get rid of this soon and always forward to the scene building thread.
-    fn build_scene(&mut self, resource_cache: &mut ResourceCache) {
+    fn build_scene(&mut self, resource_cache: &mut ResourceCache, scene_id: u64) {
         let max_texture_size = resource_cache.max_texture_size();
 
         if self.view.window_size.width > max_texture_size ||
@@ -199,7 +199,7 @@ impl Document {
             return;
         }
 
-        // The DisplayListFlattener will re-create the up-to-date current scene's pipeline epoch
+        // The DisplayListFlattener  re-create the up-to-date current scene's pipeline epoch
         // map and clip scroll tree from the information in the pending scene.
         self.current.scene.pipeline_epochs.clear();
         let old_scrolling_states = self.clip_scroll_tree.drain();
@@ -213,6 +213,7 @@ impl Document {
             &self.output_pipelines,
             &self.frame_builder_config,
             &mut self.current.scene,
+            scene_id,
         );
 
         self.clip_scroll_tree.finalize_and_apply_pending_scroll_offsets(old_scrolling_states);
@@ -233,6 +234,7 @@ impl Document {
         transaction_msg: TransactionMsg,
         document_ops: &DocumentOps,
         document_id: DocumentId,
+        scene_id: u64,
         resource_cache: &ResourceCache,
         scene_tx: &Sender<SceneBuilderRequest>,
     ) {
@@ -250,6 +252,7 @@ impl Document {
                 view: self.view.clone(),
                 font_instances: resource_cache.get_font_instances(),
                 output_pipelines: self.output_pipelines.clone(),
+                scene_id,
             })
         } else {
             None
@@ -397,6 +400,7 @@ struct PlainRenderBackend {
     frame_config: FrameBuilderConfig,
     documents: FastHashMap<DocumentId, DocumentView>,
     resources: PlainResources,
+    last_scene_id: u64,
 }
 
 /// The render backend is responsible for transforming high level display lists into
@@ -424,6 +428,7 @@ pub struct RenderBackend {
     recorder: Option<Box<ApiRecordingReceiver>>,
     sampler: Option<Box<AsyncPropertySampler + Send>>,
 
+    last_scene_id: u64,
     enable_render_on_scroll: bool,
 }
 
@@ -460,6 +465,7 @@ impl RenderBackend {
             notifier,
             recorder,
             sampler,
+            last_scene_id: 0,
             enable_render_on_scroll,
         }
     }
@@ -688,6 +694,12 @@ impl RenderBackend {
         IdNamespace(NEXT_NAMESPACE_ID.fetch_add(1, Ordering::Relaxed) as u32)
     }
 
+    pub fn make_unique_scene_id(&mut self) -> u64 {
+        // 2^64 scenes ought to be enough for anybody!
+        self.last_scene_id += 1;
+        self.last_scene_id
+    }
+
     pub fn run(&mut self, mut profile_counters: BackendProfileCounters) {
         let mut frame_counter: u32 = 0;
         let mut keep_going = true;
@@ -746,7 +758,7 @@ impl RenderBackend {
                                 document_id,
                                 transaction_msg,
                                 &mut frame_counter,
-                                &mut profile_counters
+                                &mut profile_counters,
                             );
                         }
                     },
@@ -945,7 +957,7 @@ impl RenderBackend {
                     document_id,
                     doc_msgs,
                     frame_counter,
-                    profile_counters
+                    profile_counters,
                 )
             }
         }
@@ -975,11 +987,14 @@ impl RenderBackend {
         }
 
         if transaction_msg.use_scene_builder_thread {
+            let scene_id = self.make_unique_scene_id();
             let doc = self.documents.get_mut(&document_id).unwrap();
+
             doc.forward_transaction_to_scene_builder(
                 transaction_msg,
                 &op,
                 document_id,
+                scene_id,
                 &self.resource_cache,
                 &self.scene_tx,
             );
@@ -993,11 +1008,12 @@ impl RenderBackend {
         );
 
         if op.build {
+            let scene_id = self.make_unique_scene_id();
             let doc = self.documents.get_mut(&document_id).unwrap();
             let _timer = profile_counters.total_time.timer();
             profile_scope!("build scene");
 
-            doc.build_scene(&mut self.resource_cache);
+            doc.build_scene(&mut self.resource_cache, scene_id);
             doc.render_on_hittest = true;
         }
 
@@ -1269,6 +1285,7 @@ impl RenderBackend {
                 .map(|(id, doc)| (*id, doc.view.clone()))
                 .collect(),
             resources,
+            last_scene_id: self.last_scene_id,
         };
 
         config.serialize(&backend, "backend");
@@ -1328,6 +1345,7 @@ impl RenderBackend {
         self.frame_config = backend.frame_config;
         self.enable_render_on_scroll = backend.enable_render_on_scroll;
 
+        let mut last_scene_id = backend.last_scene_id;
         for (id, view) in backend.documents {
             debug!("\tdocument {:?}", id);
             let scene_name = format!("scene-{}-{}", (id.0).0, id.1);
@@ -1362,7 +1380,8 @@ impl RenderBackend {
                     RenderedDocument::new(frame)
                 }
                 None => {
-                    doc.build_scene(&mut self.resource_cache);
+                    last_scene_id += 1;
+                    doc.build_scene(&mut self.resource_cache, last_scene_id);
                     doc.render(
                         &mut self.resource_cache,
                         &mut self.gpu_cache,

webrender/src/scene_builder.rs

@@ -57,6 +57,7 @@ pub struct SceneRequest {
     pub font_instances: FontInstanceMap,
     pub output_pipelines: FastHashSet<PipelineId>,
     pub removed_pipelines: Vec<PipelineId>,
+    pub scene_id: u64,
 }
 
 pub struct BuiltScene {