From 7675f794c13e504dce28dc14a9ddabf449a1fde0 Mon Sep 17 00:00:00 2001
From: Ethan Lin <ethlin@mozilla.com>
Date: Fri, 25 Aug 2017 16:36:15 +0800
Subject: [PATCH] Bug 1393706 - Compute display item's visibility when creating
 fallback data in layers-free mode. r=jrmuizel

MozReview-Commit-ID: 6eUnABLce2Z

--HG--
extra : rebase_source : 1a1b462897ef838c70eb8613501b940c06dd0f99
---
 gfx/layers/wr/WebRenderLayerManager.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/gfx/layers/wr/WebRenderLayerManager.cpp b/gfx/layers/wr/WebRenderLayerManager.cpp
index 41d42180b19c..f678faa2d015 100644
--- a/gfx/layers/wr/WebRenderLayerManager.cpp
+++ b/gfx/layers/wr/WebRenderLayerManager.cpp
@@ -516,6 +516,13 @@ WebRenderLayerManager::GenerateFallbackData(nsDisplayItem* aItem,
     clippedBounds = itemBounds.Intersect(clip.GetClipRect());
   }
 
+  // nsDisplayItem::Paint() may refer the variables that come from ComputeVisibility().
+  // So we should call ComputeVisibility() before painting. e.g.: nsDisplayBoxShadowInner
+  // uses mVisibleRegion in Paint() and mVisibleRegion is computed in
+  // nsDisplayBoxShadowInner::ComputeVisibility().
+  nsRegion visibleRegion(clippedBounds);
+  aItem->ComputeVisibility(aDisplayListBuilder, &visibleRegion);
+
   const int32_t appUnitsPerDevPixel = aItem->Frame()->PresContext()->AppUnitsPerDevPixel();
   LayerRect bounds = ViewAs<LayerPixel>(
       LayoutDeviceRect::FromAppUnits(clippedBounds, appUnitsPerDevPixel),