1 files changed, 16 insertions, 9 deletions
diff --git a/gfx/layers/wr/WebRenderLayerManager.cpp b/gfx/layers/wr/WebRenderLayerManager.cpp
index 66b98a7db3..c29517c696 100644
--- a/gfx/layers/wr/WebRenderLayerManager.cpp
+++ b/gfx/layers/wr/WebRenderLayerManager.cpp
@@ -96,6 +96,7 @@ bool WebRenderLayerManager::Initialize(
   }
 
   mWrChild = static_cast<WebRenderBridgeChild*>(bridge);
+  mHasFlushedThisChild = false;
 
   TextureFactoryIdentifier textureFactoryIdentifier;
   wr::MaybeIdNamespace idNamespace;
@@ -694,24 +695,30 @@ void WebRenderLayerManager::FlushRendering(wr::RenderReasons aReasons) {
   }
   MOZ_ASSERT(mWidget);
 
-  // If value of IsResizingNativeWidget() is nothing, we assume that resizing
-  // might happen.
-  bool resizing = mWidget && mWidget->IsResizingNativeWidget().valueOr(true);
+  // If widget bounds size is different from the last flush, consider
+  // this to be a resize. It's important to use GetClientSize here,
+  // because that has extra plumbing to support initial display cases
+  // where the widget doesn't yet have real bounds.
+  LayoutDeviceIntSize widgetSize = mWidget->GetClientSize();
+  bool resizing = widgetSize != mFlushWidgetSize;
+  mFlushWidgetSize = widgetSize;
 
   if (resizing) {
     aReasons = aReasons | wr::RenderReasons::RESIZE;
   }
 
-  // Limit async FlushRendering to !resizing and Win DComp.
-  // XXX relax the limitation
-  if (WrBridge()->GetCompositorUseDComp() && !resizing) {
-    cBridge->SendFlushRenderingAsync(aReasons);
-  } else if (mWidget->SynchronouslyRepaintOnResize() ||
-             StaticPrefs::layers_force_synchronous_resize()) {
+  // Check for the conditions where we we force a sync flush. The first
+  // flush for this child should always be sync. Resizes should be
+  // sometimes be sync. Everything else can be async.
+  if (!mHasFlushedThisChild ||
+      (resizing && (mWidget->SynchronouslyRepaintOnResize() ||
+                    StaticPrefs::layers_force_synchronous_resize()))) {
     cBridge->SendFlushRendering(aReasons);
   } else {
     cBridge->SendFlushRenderingAsync(aReasons);
   }
+
+  mHasFlushedThisChild = true;
 }
 
 void WebRenderLayerManager::WaitOnTransactionProcessed() {