From e54839acce2d8c967765fe5a5a363f5e69cd55ab Mon Sep 17 00:00:00 2001
From: Ryan Hunt <rhunt@eqrion.net>
Date: Tue, 27 Nov 2018 15:40:57 -0600
Subject: [PATCH] Bug 1305957 part 13 - Highlight scroll anchor when
 'layout.scroll-anchoring.highlight' is enabled. r=mattwoodrow

This commit adds a debug pref that will highlight the frames that are marked as
anchor nodes. This is helpful to debug anchor selection.

Differential Revision: https://phabricator.services.mozilla.com/D13276

--HG--
extra : rebase_source : 61109b3d967f0e4f8e5a260a71fecc01ebf22c73
extra : histedit_source : d2275fdb4edc3d7f6b006c8c7ab24fca1223998d
---
 layout/generic/ScrollAnchorContainer.cpp |  8 ++++++++
 layout/generic/nsFrame.cpp               | 12 ++++++++++++
 modules/libpref/init/StaticPrefList.h    |  6 ++++++
 3 files changed, 26 insertions(+)

diff --git a/layout/generic/ScrollAnchorContainer.cpp b/layout/generic/ScrollAnchorContainer.cpp
index 19de19a801a1..c9a40e490910 100644
--- a/layout/generic/ScrollAnchorContainer.cpp
+++ b/layout/generic/ScrollAnchorContainer.cpp
@@ -63,6 +63,14 @@ static void SetAnchorFlags(const nsIFrame* aScrolledFrame,
   }
   MOZ_ASSERT(frame,
              "The anchor node should be a descendant of the scroll frame");
+  // If needed, invalidate the frame so that we start/stop highlighting the
+  // anchor
+  if (StaticPrefs::layout_css_scroll_anchoring_highlight()) {
+    for (nsIFrame* frame = aAnchorNode->FirstContinuation(); !!frame;
+         frame = frame->GetNextContinuation()) {
+      frame->InvalidateFrame();
+    }
+  }
 }
 
 /**
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index 3c434a97ee7e..033d77174319 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -22,6 +22,7 @@
 #include "mozilla/gfx/gfxVars.h"
 #include "mozilla/gfx/PathHelpers.h"
 #include "mozilla/Sprintf.h"
+#include "mozilla/StaticPrefs.h"
 
 #include "nsCOMPtr.h"
 #include "nsFlexContainerFrame.h"
@@ -3517,6 +3518,17 @@ void nsIFrame::BuildDisplayListForChild(nsDisplayListBuilder* aBuilder,
       // Animations may change the stacking context state.
       !(child->MayHaveTransformAnimation() || child->MayHaveOpacityAnimation());
 
+  if (StaticPrefs::layout_css_scroll_anchoring_highlight()) {
+    if (child->FirstContinuation()->IsScrollAnchor()) {
+      nsRect bounds = child->GetContentRectRelativeToSelf() +
+                      aBuilder->ToReferenceFrame(child);
+      nsDisplaySolidColor* color = MakeDisplayItem<nsDisplaySolidColor>(
+          aBuilder, child, bounds, NS_RGBA(255, 0, 255, 64));
+      color->SetOverrideZIndex(INT32_MAX);
+      aLists.PositionedDescendants()->AppendToTop(color);
+    }
+  }
+
   if (doingShortcut) {
     BuildDisplayListForSimpleChild(aBuilder, child, aLists);
     return;
diff --git a/modules/libpref/init/StaticPrefList.h b/modules/libpref/init/StaticPrefList.h
index 4240efb559bd..616cb4c3f65d 100644
--- a/modules/libpref/init/StaticPrefList.h
+++ b/modules/libpref/init/StaticPrefList.h
@@ -896,6 +896,12 @@ VARCACHE_PREF(
 )
 #undef PREF_VALUE
 
+VARCACHE_PREF(
+  "layout.css.scroll-anchoring.highlight",
+   layout_css_scroll_anchoring_highlight,
+  bool, false
+)
+
 //---------------------------------------------------------------------------
 // JavaScript prefs
 //---------------------------------------------------------------------------