From 427fc1d03cb42af65bba318a08f0b751c7c51a45 Mon Sep 17 00:00:00 2001
From: David Anderson <danderson@mozilla.com>
Date: Mon, 31 Jul 2017 12:29:18 -0700
Subject: [PATCH] Include visible region changes in the cached invalid region
 for ContainerLayers. (bug 1381666 part 4, r=mattwoodrow)

---
 gfx/layers/LayerTreeInvalidation.cpp | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/gfx/layers/LayerTreeInvalidation.cpp b/gfx/layers/LayerTreeInvalidation.cpp
index 3de5968e1f5d..c138a163fcfd 100644
--- a/gfx/layers/LayerTreeInvalidation.cpp
+++ b/gfx/layers/LayerTreeInvalidation.cpp
@@ -421,10 +421,22 @@ public:
     }
 
     if (container->UseIntermediateSurface()) {
-      IntRect bounds = invalidateWholeLayer
-                       ? mLayer->GetLocalVisibleRegion().ToUnknownRegion().GetBounds()
-                       : result.GetBounds();
-      container->SetInvalidCompositeRect(bounds);
+      Maybe<IntRect> bounds;
+
+      if (!invalidateWholeLayer) {
+        bounds = Some(result.GetBounds());
+
+        // Process changes in the visible region.
+        IntRegion newVisible = mLayer->GetLocalVisibleRegion().ToUnknownRegion();
+        if (!newVisible.IsEqual(mVisibleRegion)) {
+          newVisible.XorWith(mVisibleRegion);
+          bounds = bounds->SafeUnion(newVisible.GetBounds());
+        }
+      }
+      if (!bounds) {
+        bounds = Some(mLayer->GetLocalVisibleRegion().GetBounds().ToUnknownRect());
+      }
+      container->SetInvalidCompositeRect(bounds.value());
     }
 
     if (!mLayer->Extend3DContext()) {