Backed out changeset 339795d0a51e (bug 1574746) for causing browser_startup_syncIPC.js failures CLOSED TREE

widget/gtk/nsWindow.cpp

@@ -3963,8 +3963,10 @@ nsresult nsWindow::Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
       // gfxVars, used below.
       Unused << gfxPlatform::GetPlatform();
 
+      bool useWebRender =
+          gfx::gfxVars::UseWebRender() && AllowWebRenderForThisWindow();
+
       mIsAccelerated = ComputeShouldAccelerate();
-      bool useWebRender = gfx::gfxVars::UseWebRender() && mIsAccelerated;
       MOZ_ASSERT(mIsAccelerated | !useWebRender);
 
       if (mWindowType == eWindowType_toplevel) {

widget/nsBaseWidget.cpp

@@ -823,6 +823,12 @@ bool nsBaseWidget::IsSmallPopup() const {
 }
 
 bool nsBaseWidget::ComputeShouldAccelerate() {
+  if (gfx::gfxVars::UseWebRender() && !AllowWebRenderForThisWindow()) {
+    // If WebRender is enabled, non-WebRender widgets use the basic compositor
+    // (at least for now), even though they would get an accelerated compositor
+    // if WebRender wasn't enabled.
+    return false;
+  }
   return gfx::gfxConfig::IsEnabled(gfx::Feature::HW_COMPOSITING) &&
          WidgetTypeSupportsAcceleration();
 }
@@ -835,6 +841,13 @@ bool nsBaseWidget::UseAPZ() {
             StaticPrefs::apz_popups_enabled())));
 }
 
+bool nsBaseWidget::AllowWebRenderForThisWindow() {
+  return WindowType() == eWindowType_toplevel ||
+         WindowType() == eWindowType_child ||
+         WindowType() == eWindowType_dialog ||
+         (WindowType() == eWindowType_popup && HasRemoteContent());
+}
+
 void nsBaseWidget::CreateCompositor() {
   LayoutDeviceIntRect rect = GetBounds();
   CreateCompositor(rect.Width(), rect.Height());
@@ -1199,8 +1212,9 @@ already_AddRefed<LayerManager> nsBaseWidget::CreateCompositorSession(
     // If widget type does not supports acceleration, we use ClientLayerManager
     // even when gfxVars::UseWebRender() is true. WebRender could coexist only
     // with BasicCompositor.
-    bool enableWR =
-        gfx::gfxVars::UseWebRender() && WidgetTypeSupportsAcceleration();
+    bool enableWR = gfx::gfxVars::UseWebRender() &&
+                    WidgetTypeSupportsAcceleration() &&
+                    AllowWebRenderForThisWindow();
     bool enableAPZ = UseAPZ();
     CompositorOptions options(enableAPZ, enableWR);