Fix resize jank on Linux with OMTC (bug 926618, r=mattwoodrow).

gfx/layers/client/ClientLayerManager.cpp

@@ -43,6 +43,7 @@ ClientLayerManager::ClientLayerManager(nsIWidget* aWidget)
   , mIsRepeatTransaction(false)
   , mTransactionIncomplete(false)
   , mCompositorMightResample(false)
+  , mNeedsComposite(false)
 {
   MOZ_COUNT_CTOR(ClientLayerManager);
 }
@@ -299,8 +300,9 @@ ClientLayerManager::ForwardTransaction()
   mPhase = PHASE_FORWARD;
 
   // forward this transaction's changeset to our LayerManagerComposite
+  bool sent;
   AutoInfallibleTArray<EditReply, 10> replies;
-  if (HasShadowManager() && ShadowLayerForwarder::EndTransaction(&replies)) {
+  if (HasShadowManager() && ShadowLayerForwarder::EndTransaction(&replies, &sent)) {
     for (nsTArray<EditReply>::size_type i = 0; i < replies.Length(); ++i) {
       const EditReply& reply = replies[i];
 
@@ -349,6 +351,10 @@ ClientLayerManager::ForwardTransaction()
         NS_RUNTIMEABORT("not reached");
       }
     }
+
+    if (sent) {
+      mNeedsComposite = false;
+    }
   } else if (HasShadowManager()) {
     NS_WARNING("failed to forward Layers transaction");
   }

gfx/layers/client/ClientLayerManager.h

@@ -142,6 +142,12 @@ public:
 #endif
   bool InTransaction() { return mPhase != PHASE_NONE; }
 
+  void SetNeedsComposite(bool aNeedsComposite)
+  {
+    mNeedsComposite = aNeedsComposite;
+  }
+  bool NeedsComposite() const { return mNeedsComposite; }
+
 protected:
   enum TransactionPhase {
     PHASE_NONE, PHASE_CONSTRUCTION, PHASE_DRAWING, PHASE_FORWARD
@@ -200,6 +206,7 @@ private:
   bool mIsRepeatTransaction;
   bool mTransactionIncomplete;
   bool mCompositorMightResample;
+  bool mNeedsComposite;
 };
 
 class ClientLayer : public ShadowableLayer

gfx/layers/ipc/ShadowLayers.cpp

@@ -467,8 +467,10 @@ ShadowLayerForwarder::UseTexture(CompositableClient* aCompositable,
 }
 
 bool
-ShadowLayerForwarder::EndTransaction(InfallibleTArray<EditReply>* aReplies)
+ShadowLayerForwarder::EndTransaction(InfallibleTArray<EditReply>* aReplies, bool* aSent)
 {
+  *aSent = false;
+
   PROFILER_LABEL("ShadowLayerForwarder", "EndTranscation");
   RenderTraceScope rendertrace("Foward Transaction", "000091");
   NS_ABORT_IF_FALSE(HasShadowManager(), "no manager to forward to");
@@ -582,6 +584,7 @@ ShadowLayerForwarder::EndTransaction(InfallibleTArray<EditReply>* aReplies)
     }
   }
 
+  *aSent = true;
   mIsFirstPaint = false;
   MOZ_LAYERS_LOG(("[LayersForwarder] ... done"));
   return true;

gfx/layers/ipc/ShadowLayers.h

@@ -334,7 +334,7 @@ public:
    * |aReplies| are directions from the LayerManagerComposite to the
    * caller of EndTransaction().
    */
-  bool EndTransaction(InfallibleTArray<EditReply>* aReplies);
+  bool EndTransaction(InfallibleTArray<EditReply>* aReplies, bool* aSent);
 
   /**
    * Set an actor through which layer updates will be pushed.

widget/gtk/nsWindow.cpp

@@ -1980,10 +1980,17 @@ nsWindow::OnExposeEvent(cairo_t *cr)
     if (!listener)
         return FALSE;
 
-    // Do an early async composite so that we at least have something on screen
-    // in the right place, even if the content is out of date.
-    if (GetLayerManager()->GetBackendType() == LAYERS_CLIENT && mCompositorParent) {
-        mCompositorParent->ScheduleRenderOnCompositorThread();
+    ClientLayerManager *clientLayers =
+        (GetLayerManager()->GetBackendType() == LAYERS_CLIENT)
+        ? static_cast<ClientLayerManager*>(GetLayerManager())
+        : nullptr;
+
+    if (clientLayers && mCompositorParent &&
+        !gdk_screen_is_composited(gdk_window_get_screen(mGdkWindow)))
+    {
+        // We need to paint to the screen even if nothing changed, since if we
+        // don't have a compositing window manager, our pixels could be stale.
+        clientLayers->SetNeedsComposite(true);
     }
 
     // Dispatch WillPaintWindow notification to allow scripts etc. to run
@@ -2004,6 +2011,11 @@ nsWindow::OnExposeEvent(cairo_t *cr)
             return FALSE;
     }
 
+    if (clientLayers && mCompositorParent && clientLayers->NeedsComposite()) {
+        mCompositorParent->ScheduleRenderOnCompositorThread();
+        clientLayers->SetNeedsComposite(false);
+    }
+
 #if (MOZ_WIDGET_GTK == 2)
     GdkRectangle *rects;
     gint nrects;