Bug 1501382 - Cull items within an opacity:0 container when using WebRender. r=kats

Depends on D14230

Differential Revision: https://phabricator.services.mozilla.com/D14231

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

gfx/layers/wr/WebRenderCommandBuilder.cpp

@@ -1541,6 +1541,13 @@ void WebRenderCommandBuilder::CreateWebRenderCommandsFromDisplayList(
       MOZ_ASSERT(item && itemType == item->GetType());
     }
 
+    if (mForEventsAndPluginsOnly &&
+        (itemType != DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO &&
+         itemType != DisplayItemType::TYPE_PLUGIN)) {
+      // Only process hit test info items or plugin items.
+      continue;
+    }
+
     bool forceNewLayerData = false;
     size_t layerCountBeforeRecursing = mLayerScrollData.size();
     if (apzEnabled) {
@@ -1594,6 +1601,13 @@ void WebRenderCommandBuilder::CreateWebRenderCommandsFromDisplayList(
         GP("attempting to enter the grouping code\n");
       }
 
+      AutoRestore<bool> restoreForEventsAndPluginsOnly(
+          mForEventsAndPluginsOnly);
+      if (itemType == DisplayItemType::TYPE_OPACITY &&
+          static_cast<nsDisplayOpacity*>(item)->ForEventsAndPluginsOnly()) {
+        mForEventsAndPluginsOnly = true;
+      }
+
       if (dumpEnabled) {
         std::stringstream ss;
         nsFrame::PrintDisplayItem(aDisplayListBuilder, item, ss,

gfx/layers/wr/WebRenderCommandBuilder.h

@@ -42,6 +42,7 @@ class WebRenderCommandBuilder {
         mBuilderDumpIndex(0),
         mDumpIndent(0),
         mDoGrouping(false),
+        mForEventsAndPluginsOnly(false),
         mContainsSVGGroup(false) {}
 
   void Destroy();
@@ -199,6 +200,10 @@ class WebRenderCommandBuilder {
   // blob image.
   bool mDoGrouping;
 
+  // True if we're currently within an opacity:0 container, and only
+  // plugin and hit test items should be considered.
+  bool mForEventsAndPluginsOnly;
+
   // True if the most recently build display list contained an svg that
   // we did grouping for.
   bool mContainsSVGGroup;

layout/painting/nsDisplayList.h

@@ -5336,6 +5336,8 @@ class nsDisplayOpacity : public nsDisplayWrapList {
 
   float GetOpacity() const { return mOpacity; }
 
+  bool ForEventsAndPluginsOnly() const { return mForEventsAndPluginsOnly; }
+
  private:
   bool ApplyOpacityToChildren(nsDisplayListBuilder* aBuilder);
   bool IsEffectsWrapper() const;