Bug 873944 - Add FlushRendering API to the compositor interface. r=nrc

gfx/layers/Layers.h

@@ -466,6 +466,15 @@ public:
    */
   virtual void SetIsFirstPaint() {}
 
+  /**
+   * Make sure that the previous transaction has been entirely
+   * completed.
+   *
+   * Note: This may sychronously wait on a remote compositor
+   * to complete rendering.
+   */
+  virtual void FlushRendering() { }
+
   // We always declare the following logging symbols, because it's
   // extremely tricky to conditionally declare them.  However, for
   // ifndef MOZ_LAYERS_HAVE_LOG builds, they only have trivial

gfx/layers/client/ClientLayerManager.cpp

@@ -260,6 +260,16 @@ ClientLayerManager::MakeSnapshotIfRequired()
   mShadowTarget = nullptr;
 }
 
+void
+ClientLayerManager::FlushRendering()
+{
+  if (mWidget) {
+    if (CompositorChild* remoteRenderer = mWidget->GetRemoteRenderer()) {
+      remoteRenderer->SendFlushRendering();
+    }
+  }
+}
+
 void
 ClientLayerManager::ForwardTransaction()
 {

gfx/layers/client/ClientLayerManager.h

@@ -53,6 +53,8 @@ public:
   virtual already_AddRefed<ColorLayer> CreateColorLayer();
   virtual already_AddRefed<RefLayer> CreateRefLayer();
 
+  virtual void FlushRendering() MOZ_OVERRIDE;
+
   ShadowableLayer* Hold(Layer* aLayer);
 
   bool HasShadowManager() const { return ShadowLayerForwarder::HasShadowManager(); }

gfx/layers/ipc/CompositorParent.cpp

@@ -249,6 +249,18 @@ CompositorParent::RecvMakeSnapshot(const SurfaceDescriptor& aInSnapshot,
   return true;
 }
 
+bool
+CompositorParent::RecvFlushRendering()
+{
+  // If we're waiting to do a composite, then cancel it
+  // and do it immediately instead.
+  if (mCurrentCompositeTask) {
+    mCurrentCompositeTask->Cancel();
+    ComposeToTarget(nullptr);
+  }
+  return true;
+}
+
 void
 CompositorParent::ActorDestroy(ActorDestroyReason why)
 {
@@ -743,6 +755,7 @@ public:
   virtual bool RecvMakeSnapshot(const SurfaceDescriptor& aInSnapshot,
                                 SurfaceDescriptor* aOutSnapshot)
   { return true; }
+  virtual bool RecvFlushRendering() MOZ_OVERRIDE { return true; }
 
   virtual PLayerTransactionParent*
     AllocPLayerTransaction(const LayersBackend& aBackendType,

gfx/layers/ipc/CompositorParent.h

@@ -55,6 +55,7 @@ public:
   virtual bool RecvResume() MOZ_OVERRIDE;
   virtual bool RecvMakeSnapshot(const SurfaceDescriptor& aInSnapshot,
                                 SurfaceDescriptor* aOutSnapshot);
+  virtual bool RecvFlushRendering() MOZ_OVERRIDE;
 
   virtual void ActorDestroy(ActorDestroyReason why) MOZ_OVERRIDE;
 

gfx/layers/ipc/PCompositor.ipdl

@@ -53,6 +53,10 @@ parent:
   sync MakeSnapshot(SurfaceDescriptor inSnapshot)
     returns (SurfaceDescriptor outSnapshot);
 
+  // Make sure any pending composites are started immediately and
+  // block until they are completed.
+  sync FlushRendering();
+
   sync PLayerTransaction(LayersBackend layersBackendHint, uint64_t id)
     returns (TextureFactoryIdentifier textureFactoryIdentifier);
 };