Bug 1574745 - Reorder layer rendering invocations. r=mattwoodrow

This change groups the work that has to be done per compositing tile.

Differential Revision: https://phabricator.services.mozilla.com/D43878

--HG--
extra : moz-landing-system : lando

gfx/layers/composite/LayerManagerComposite.cpp

@@ -1022,14 +1022,7 @@ bool LayerManagerComposite::Render(const nsIntRegion& aInvalidRegion,
                                             ScreenPoint(0.0f, offset));
 #endif
 
-  RefPtr<CompositingRenderTarget> previousTarget;
-  if (haveLayerEffects) {
-    previousTarget = PushGroupForLayerEffects();
-  } else {
-    mTwoPassTmpTarget = nullptr;
-  }
-
-  // Render our layers.
+  // Prepare our layers.
   {
     Diagnostics::Record record(mRenderStartTime);
     RootLayer()->Prepare(RenderTargetIntRect::FromUnknownRect(clipRect));
@@ -1037,34 +1030,37 @@ bool LayerManagerComposite::Render(const nsIntRegion& aInvalidRegion,
       mDiagnostics->RecordPrepareTime(record.Duration());
     }
   }
-  // Execute draw commands.
+
   {
     Diagnostics::Record record;
+    RefPtr<CompositingRenderTarget> previousTarget;
+    if (haveLayerEffects) {
+      previousTarget = PushGroupForLayerEffects();
+    } else {
+      mTwoPassTmpTarget = nullptr;
+    }
+
+    // Execute draw commands.
     RootLayer()->RenderLayer(clipRect, Nothing());
+
+    if (mTwoPassTmpTarget) {
+      MOZ_ASSERT(haveLayerEffects);
+      PopGroupForLayerEffects(previousTarget, clipRect, grayscaleVal, invertVal,
+                              contrastVal);
+    }
+    if (!mRegionToClear.IsEmpty()) {
+      for (auto iter = mRegionToClear.RectIter(); !iter.Done(); iter.Next()) {
+        mCompositor->ClearRect(Rect(iter.Get()));
+      }
+    }
+    mCompositor->NormalDrawingDone();
     if (record.Recording()) {
       mDiagnostics->RecordCompositeTime(record.Duration());
     }
   }
+
   RootLayer()->Cleanup();
 
-  if (!mRegionToClear.IsEmpty()) {
-    for (auto iter = mRegionToClear.RectIter(); !iter.Done(); iter.Next()) {
-      mCompositor->ClearRect(Rect(iter.Get()));
-    }
-  }
-
-  if (mTwoPassTmpTarget) {
-    MOZ_ASSERT(haveLayerEffects);
-    PopGroupForLayerEffects(previousTarget, clipRect, grayscaleVal, invertVal,
-                            contrastVal);
-  }
-
-  // Allow widget to render a custom foreground.
-  mCompositor->GetWidget()->DrawWindowOverlay(
-      &widgetContext, LayoutDeviceIntRect::FromUnknownRect(bounds));
-
-  mCompositor->NormalDrawingDone();
-
   mProfilerScreenshotGrabber.MaybeGrabScreenshot(mCompositor);
 
   if (mCompositionRecorder) {
@@ -1081,6 +1077,10 @@ bool LayerManagerComposite::Render(const nsIntRegion& aInvalidRegion,
     }
   }
 
+  // Allow widget to render a custom foreground.
+  mCompositor->GetWidget()->DrawWindowOverlay(
+      &widgetContext, LayoutDeviceIntRect::FromUnknownRect(bounds));
+
 #if defined(MOZ_WIDGET_ANDROID)
   // Depending on the content shift the toolbar may be rendered on top of
   // some of the content so it must be rendered after the content.