Bug 1410777 - Force a full transaction for WR when the window overlay changes. r=mstange

The window buttons are drawn as part of the AddWindowOverlayWebRenderCommands
function which is invoked in the full-transaction codepath. It should be possible
to have the empty transaction codepath simply update the image (without building
a full WR display list) and do a recomposite. That would be more performant but
it requires some plumbing to build and ship across a IpcResourceUpdateQueue on
empty transactions.

MozReview-Commit-ID: 2Mrb0wELD6E

--HG--
extra : rebase_source : 9a94c32f94403050835bf3445176f4fe2c1579fa

gfx/layers/wr/WebRenderLayerManager.cpp

@@ -28,6 +28,7 @@ namespace layers {
 WebRenderLayerManager::WebRenderLayerManager(nsIWidget* aWidget)
   : mWidget(aWidget)
   , mLatestTransactionId(0)
+  , mWindowOverlayChanged(false)
   , mNeedsComposite(false)
   , mIsFirstPaint(false)
   , mTarget(nullptr)
@@ -174,6 +175,16 @@ WebRenderLayerManager::BeginTransaction()
 bool
 WebRenderLayerManager::EndEmptyTransaction(EndTransactionFlags aFlags)
 {
+  if (mWindowOverlayChanged) {
+    // If the window overlay changed then we can't do an empty transaction
+    // because we need to repaint the window overlay which we only currently
+    // support in a full transaction.
+    // XXX If we end up hitting this branch a lot we can probably optimize it
+    // by just sending an updated window overlay image instead of rebuilding
+    // the entire WR display list.
+    return false;
+  }
+
   // With the WebRenderLayerManager we reject attempts to set most kind of
   // "pending data" for empty transactions. Any place that attempts to update
   // transforms or scroll offset, for example, will get failure return values
@@ -275,6 +286,8 @@ WebRenderLayerManager::EndTransactionWithoutLayer(nsDisplayList* aDisplayList,
                                                   contentSize);
 
   mWidget->AddWindowOverlayWebRenderCommands(WrBridge(), builder, resourceUpdates);
+  mWindowOverlayChanged = false;
+
   WrBridge()->ClearReadLocks();
 
   if (AsyncPanZoomEnabled()) {

gfx/layers/wr/WebRenderLayerManager.h

@@ -154,6 +154,7 @@ public:
   WebRenderScrollData& GetScrollData() { return mScrollData; }
 
   void WrUpdated();
+  void WindowOverlayChanged() { mWindowOverlayChanged = true; }
 
 private:
   /**
@@ -191,6 +192,7 @@ private:
   // APZ to do it's job
   WebRenderScrollData mScrollData;
 
+  bool mWindowOverlayChanged;
   bool mNeedsComposite;
   bool mIsFirstPaint;
   FocusTarget mFocusTarget;

widget/cocoa/nsChildView.mm

@@ -71,6 +71,7 @@
 #include "mozilla/layers/InputAPZContext.h"
 #include "mozilla/layers/IpcResourceUpdateQueue.h"
 #include "mozilla/layers/WebRenderBridgeChild.h"
+#include "mozilla/layers/WebRenderLayerManager.h"
 #include "mozilla/webrender/WebRenderAPI.h"
 #include "mozilla/widget/CompositorWidget.h"
 #include "gfxUtils.h"
@@ -4021,6 +4022,8 @@ NSEvent* gLastDragMouseDownEvent = nil;
     if ([self isUsingOpenGL]) {
       if (ShadowLayerForwarder* slf = mGeckoChild->GetLayerManager()->AsShadowForwarder()) {
         slf->WindowOverlayChanged();
+      } else if (WebRenderLayerManager* wrlm = mGeckoChild->GetLayerManager()->AsWebRenderLayerManager()) {
+        wrlm->WindowOverlayChanged();
       }
     }