Composite only when needed.

gfx/layers/ipc/CompositorChild.cpp

@@ -59,7 +59,7 @@ CompositorChild::CompositorChild(Thread *aCompositorThread, LayerManager *aLayer
 
 CompositorChild::~CompositorChild()
 {
-  printf("del\n");
+  printf("del compositor child\n");
   MOZ_COUNT_DTOR(CompositorChild);
 }
 
@@ -76,7 +76,7 @@ CompositorChild::CreateCompositor(LayerManager *aLayerManager)
   if (compositorThread->Start()) {
     MessageLoop *parentMessageLoop = MessageLoop::current();
     MessageLoop *childMessageLoop = compositorThread->message_loop();
-    CompositorParent *compositorParent = new CompositorParent();
+    CompositorParent* compositorParent = new CompositorParent();
     CompositorChild *compositorChild = new CompositorChild(compositorThread, aLayerManager);
     mozilla::ipc::AsyncChannel *parentChannel =
       compositorParent->GetIPCChannel();
@@ -87,6 +87,7 @@ CompositorChild::CreateCompositor(LayerManager *aLayerManager)
 
     compositorChild->Open(parentChannel, childMessageLoop, childSide);
     compositorChild->CallInit();
+    compositorChild->mCompositorParent = compositorParent;
 
     return compositorChild;
   }

gfx/layers/ipc/CompositorChild.h

@@ -42,7 +42,6 @@
 
 #include "mozilla/layers/PCompositorChild.h"
 
-
 namespace base {
   class Thread;
 }
@@ -53,6 +52,7 @@ namespace mozilla {
 namespace layers {
 
 class LayerManager;
+class CompositorParent;
 
 class CompositorChild : public PCompositorChild
 {
@@ -75,6 +75,7 @@ protected:
 private:
   Thread *mCompositorThread;
   LayerManager *mLayerManager;
+  nsRefPtr<CompositorParent> mCompositorParent;
 
   DISALLOW_EVIL_CONSTRUCTORS(CompositorChild);
 };

gfx/layers/ipc/CompositorParent.cpp

@@ -77,16 +77,22 @@ CompositorParent::AnswerStop()
 }
 
 void
-CompositorParent::Composite()
+CompositorParent::RequestComposition()
 {
   CancelableTask *composeTask = NewRunnableMethod(this, &CompositorParent::Composite);
-  MessageLoop::current()->PostDelayedTask(FROM_HERE, composeTask, 10);
+  MessageLoop::current()->PostTask(FROM_HERE, composeTask);
+}
 
-  if (!mLayerManager)
+void
+CompositorParent::Composite()
+{
+  if (!mLayerManager) {
+    CancelableTask *composeTask = NewRunnableMethod(this, &CompositorParent::Composite);
+    MessageLoop::current()->PostDelayedTask(FROM_HERE, composeTask, 10);
     return;
+  }
 
   mLayerManager->EndEmptyTransaction();
-
 }
 
 PLayersParent*

gfx/layers/ipc/CompositorParent.h

@@ -60,6 +60,8 @@ public:
   bool AnswerInit();
   bool AnswerStop();
 
+  void RequestComposition();
+
   virtual mozilla::layout::RenderFrameParent* GetRenderFrameParent() { return NULL; }
   virtual CompositorParent* GetCompositorParent() { return this; }
 

gfx/layers/ipc/ShadowLayersParent.cpp

@@ -47,6 +47,7 @@
 #include "mozilla/unused.h"
 
 #include "mozilla/layout/RenderFrameParent.h"
+#include "CompositorParent.h"
 
 #include "gfxSharedImageSurface.h"
 
@@ -395,6 +396,9 @@ ShadowLayersParent::RecvUpdate(const InfallibleTArray<Edit>& cset,
     Frame()->ShadowLayersUpdated();
   }
 
+  if (mHost->GetCompositorParent()) {
+    mHost->GetCompositorParent()->RequestComposition();
+  }
   return true;
 }