Bug 1372912 - Make the clip id more strongly typed. r=jrmuizel,mrobinson

This patch is not really needed, but it avoids accidental conversion
between FrameMetrics::ViewID (which represents a scrolling clip) and a
uint64_t id for a non-scrolling clip.

MozReview-Commit-ID: BU7p4WNocXa

--HG--
extra : rebase_source : 0cf69ca0a7b716bd9ad5c3cef114a3b99ec00e1b

gfx/layers/wr/ScrollingLayersHelper.cpp

@@ -84,7 +84,7 @@ ScrollingLayersHelper::ScrollingLayersHelper(WebRenderLayer* aLayer,
   if (layer->GetIsFixedPosition()) {
     FrameMetrics::ViewID fixedFor = layer->GetFixedPositionScrollContainerId();
     Maybe<FrameMetrics::ViewID> scrollsWith = mBuilder->ParentScrollIdFor(fixedFor);
-    Maybe<uint64_t> clipId = mBuilder->TopmostClipId();
+    Maybe<wr::WrClipId> clipId = mBuilder->TopmostClipId();
     // Default to 0 if there is no ancestor, because 0 refers to the root scrollframe.
     mBuilder->PushClipAndScrollInfo(scrollsWith.valueOr(0), clipId.ptrOr(nullptr));
   }

gfx/webrender_bindings/WebRenderAPI.cpp

@@ -587,13 +587,13 @@ DisplayListBuilder::PushClip(const WrRect& aClipRect,
   WRDL_LOG("PushClip id=%" PRIu64 " r=%s m=%p b=%s\n", clip_id,
       Stringify(aClipRect).c_str(), aMask,
       aMask ? Stringify(aMask->rect).c_str() : "none");
-  mClipIdStack.push_back(clip_id);
+  mClipIdStack.push_back(WrClipId { clip_id });
 }
 
 void
 DisplayListBuilder::PopClip()
 {
-  WRDL_LOG("PopClip id=%" PRIu64 "\n", mClipIdStack.back());
+  WRDL_LOG("PopClip id=%" PRIu64 "\n", mClipIdStack.back().id);
   mClipIdStack.pop_back();
   wr_dp_pop_clip(mWrState);
 }
@@ -627,11 +627,12 @@ DisplayListBuilder::PopScrollLayer()
 
 void
 DisplayListBuilder::PushClipAndScrollInfo(const layers::FrameMetrics::ViewID& aScrollId,
-                                          const uint64_t* aClipId)
+                                          const WrClipId* aClipId)
 {
   WRDL_LOG("PushClipAndScroll s=%" PRIu64 " c=%s\n", aScrollId,
-      aClipId ? Stringify(*aClipId).c_str() : "none");
-  wr_dp_push_clip_and_scroll_info(mWrState, aScrollId, aClipId);
+      aClipId ? Stringify(aClipId->id).c_str() : "none");
+  wr_dp_push_clip_and_scroll_info(mWrState, aScrollId,
+      aClipId ? &(aClipId->id) : nullptr);
 }
 
 void
@@ -891,7 +892,7 @@ DisplayListBuilder::PushClipRegion(const WrRect& aMain,
                                 aMask);
 }
 
-Maybe<uint64_t>
+Maybe<WrClipId>
 DisplayListBuilder::TopmostClipId()
 {
   if (mClipIdStack.empty()) {

gfx/webrender_bindings/WebRenderAPI.h

@@ -168,7 +168,7 @@ public:
   void PopScrollLayer();
 
   void PushClipAndScrollInfo(const layers::FrameMetrics::ViewID& aScrollId,
-                             const uint64_t* aClipId);
+                             const WrClipId* aClipId);
   void PopClipAndScrollInfo();
 
   void PushRect(const WrRect& aBounds,
@@ -292,7 +292,7 @@ public:
   // Returns the clip id that was most recently pushed with PushClip and that
   // has not yet been popped with PopClip. Return Nothing() if the clip stack
   // is empty.
-  Maybe<uint64_t> TopmostClipId();
+  Maybe<WrClipId> TopmostClipId();
   // Returns the scroll id that was pushed just before the given scroll id.
   // If the given scroll id is not in the stack of active scrolled layers, or if
   // it is the rootmost scroll id (and therefore has no ancestor), this function
@@ -308,7 +308,7 @@ protected:
   // (by PushClip and PushScrollLayer, respectively) and are still active.
   // This is helpful for knowing e.g. what the ancestor scroll id of a particular
   // scroll id is, and doing other "queries" of current state.
-  std::vector<uint64_t> mClipIdStack;
+  std::vector<WrClipId> mClipIdStack;
   std::vector<layers::FrameMetrics::ViewID> mScrollIdStack;
 
   friend class WebRenderAPI;

gfx/webrender_bindings/WebRenderTypes.h

@@ -584,6 +584,14 @@ static inline WrFilterOp ToWrFilterOp(const layers::CSSFilter& filter) {
   };
 }
 
+// Corresponds to an "internal" webrender clip id. That is, a
+// ClipId::Clip(x,pipeline_id) maps to a WrClipId{x}. We use a struct wrapper
+// instead of a typedef so that this is a distinct type from FrameMetrics::ViewID
+// and the compiler will catch accidental conversions between the two.
+struct WrClipId {
+  uint64_t id;
+};
+
 } // namespace wr
 } // namespace mozilla