Bug 1570721 - Simplify emulated medium setup in nsPresContext. r=heycam

Differential Revision: https://phabricator.services.mozilla.com/D40246

layout/base/nsDocumentViewer.cpp

@@ -318,6 +318,8 @@ class nsDocumentViewer final : public nsIContentViewer,
   // nsIDocumentViewerPrint Printing Methods
   NS_DECL_NSIDOCUMENTVIEWERPRINT
 
+  void EmulateMediumInternal(nsAtom*);
+
  protected:
   virtual ~nsDocumentViewer();
 
@@ -2957,61 +2959,42 @@ nsDocumentViewer::GetAuthorStyleDisabled(bool* aStyleDisabled) {
 }
 
 static bool ExtResourceEmulateMedium(Document* aDocument, void* aClosure) {
-  nsPresContext* ctxt = aDocument->GetPresContext();
-  if (ctxt) {
-    const nsAString* mediaType = static_cast<nsAString*>(aClosure);
-    ctxt->EmulateMedium(*mediaType);
+  if (nsPresContext* pc = aDocument->GetPresContext()) {
+    pc->EmulateMedium(static_cast<nsAtom*>(aClosure));
   }
 
   return true;
 }
 
 static void ChildEmulateMedium(nsDocumentViewer* aChild, void* aClosure) {
-  const nsAString* mediaType = static_cast<nsAString*>(aClosure);
-  aChild->EmulateMedium(*mediaType);
+  aChild->EmulateMediumInternal(static_cast<nsAtom*>(aClosure));
+}
+
+void nsDocumentViewer::EmulateMediumInternal(nsAtom* aMedia) {
+  if (mPresContext) {
+    mPresContext->EmulateMedium(aMedia);
+  }
+
+  CallChildren(ChildEmulateMedium, aMedia);
+
+  if (mDocument) {
+    mDocument->EnumerateExternalResources(ExtResourceEmulateMedium, aMedia);
+  }
 }
 
 NS_IMETHODIMP
 nsDocumentViewer::EmulateMedium(const nsAString& aMediaType) {
-  if (mPresContext) {
-    mPresContext->EmulateMedium(aMediaType);
-  }
-  CallChildren(ChildEmulateMedium, const_cast<nsAString*>(&aMediaType));
-
-  if (mDocument) {
-    mDocument->EnumerateExternalResources(ExtResourceEmulateMedium,
-                                          const_cast<nsAString*>(&aMediaType));
-  }
+  nsAutoString mediaType;
+  nsContentUtils::ASCIIToLower(aMediaType, mediaType);
+  RefPtr<nsAtom> media = NS_Atomize(mediaType);
 
+  EmulateMediumInternal(media);
   return NS_OK;
 }
 
-static bool ExtResourceStopEmulatingMedium(Document* aDocument,
-                                           void* aClosure) {
-  nsPresContext* ctxt = aDocument->GetPresContext();
-  if (ctxt) {
-    ctxt->StopEmulatingMedium();
-  }
-
-  return true;
-}
-
-static void ChildStopEmulatingMedium(nsIContentViewer* aChild, void* aClosure) {
-  aChild->StopEmulatingMedium();
-}
-
 NS_IMETHODIMP
 nsDocumentViewer::StopEmulatingMedium() {
-  if (mPresContext) {
-    mPresContext->StopEmulatingMedium();
-  }
-  CallChildren(ChildStopEmulatingMedium, nullptr);
-
-  if (mDocument) {
-    mDocument->EnumerateExternalResources(ExtResourceStopEmulatingMedium,
-                                          nullptr);
-  }
-
+  EmulateMediumInternal(nullptr);
   return NS_OK;
 }
 

layout/base/nsPresContext.cpp

@@ -144,7 +144,6 @@ nsPresContext::nsPresContext(dom::Document* aDocument, nsPresContextType aType)
       mPresShell(nullptr),
       mDocument(aDocument),
       mMedium(aType == eContext_Galley ? nsGkAtoms::screen : nsGkAtoms::print),
-      mMediaEmulated(mMedium),
       mInflationDisabledForShrinkWrap(false),
       mSystemFontScale(1.0),
       mTextZoom(1.0),
@@ -186,7 +185,6 @@ nsPresContext::nsPresContext(dom::Document* aDocument, nsPresContextType aType)
       mPendingUIResolutionChanged(false),
       mPrefChangePendingNeedsReflow(false),
       mPostedPrefChangedRunnable(false),
-      mIsEmulatingMedia(false),
       mIsGlyph(false),
       mUsesRootEMUnits(false),
       mUsesExChUnits(false),
@@ -1423,27 +1421,15 @@ void nsPresContext::UIResolutionChangedInternalScale(double aScale) {
                                    &aScale);
 }
 
-void nsPresContext::EmulateMedium(const nsAString& aMediaType) {
-  nsAtom* previousMedium = Medium();
-  mIsEmulatingMedia = true;
-
-  nsAutoString mediaType;
-  nsContentUtils::ASCIIToLower(aMediaType, mediaType);
-
-  mMediaEmulated = NS_Atomize(mediaType);
+void nsPresContext::EmulateMedium(nsAtom* aMediaType) {
+  MOZ_ASSERT(!aMediaType || aMediaType->IsAsciiLowercase());
+  RefPtr<const nsAtom> previousMedium = Medium();
+  mMediaEmulated = aMediaType;
   if (mMediaEmulated != previousMedium && mPresShell) {
     MediaFeatureValuesChanged({MediaFeatureChangeReason::MediumChange});
   }
 }
 
-void nsPresContext::StopEmulatingMedium() {
-  nsAtom* previousMedium = Medium();
-  mIsEmulatingMedia = false;
-  if (Medium() != previousMedium) {
-    MediaFeatureValuesChanged({MediaFeatureChangeReason::MediumChange});
-  }
-}
-
 void nsPresContext::ContentLanguageChanged() {
   PostRebuildAllStyleDataEvent(nsChangeHint(0),
                                RestyleHint::RecascadeSubtree());

layout/base/nsPresContext.h

@@ -303,21 +303,18 @@ class nsPresContext : public nsISupports,
   /**
    * Get medium of presentation
    */
-  nsAtom* Medium() {
-    if (!mIsEmulatingMedia) return mMedium;
-    return mMediaEmulated;
+  const nsAtom* Medium() {
+    MOZ_ASSERT(mMedium);
+    return mMediaEmulated ? mMediaEmulated.get() : mMedium;
   }
 
   /*
    * Render the document as if being viewed on a device with the specified
    * media type.
+   *
+   * If passed null, it stops emulating.
    */
-  void EmulateMedium(const nsAString& aMediaType);
-
-  /*
-   * Restore the viewer's natural medium
-   */
-  void StopEmulatingMedium();
+  void EmulateMedium(nsAtom* aMediaType);
 
   /** Get a cached integer pref, by its type */
   // *  - initially created for bugs 30910, 61883, 74186, 84398
@@ -1119,8 +1116,7 @@ class nsPresContext : public nsISupports,
   mozilla::UniquePtr<nsAnimationManager> mAnimationManager;
   mozilla::UniquePtr<mozilla::RestyleManager> mRestyleManager;
   RefPtr<mozilla::CounterStyleManager> mCounterStyleManager;
-  nsAtom* MOZ_UNSAFE_REF(
-      "always a static atom") mMedium;  // initialized by subclass ctors
+  const nsStaticAtom* mMedium;
   RefPtr<nsAtom> mMediaEmulated;
   RefPtr<gfxFontFeatureValueSet> mFontFeatureValuesLookup;
 
@@ -1221,7 +1217,6 @@ class nsPresContext : public nsISupports,
   unsigned mPendingUIResolutionChanged : 1;
   unsigned mPrefChangePendingNeedsReflow : 1;
   unsigned mPostedPrefChangedRunnable : 1;
-  unsigned mIsEmulatingMedia : 1;
 
   // Are we currently drawing an SVG glyph?
   unsigned mIsGlyph : 1;

servo/components/style/gecko/media_queries.rs

@@ -213,12 +213,11 @@ impl Device {
             None => return MediaType::screen(),
         };
 
-        // Gecko allows emulating random media with mIsEmulatingMedia and
-        // mMediaEmulated.
-        let medium_to_use = if pc.mIsEmulatingMedia() != 0 {
+        // Gecko allows emulating random media with mMediaEmulated.
+        let medium_to_use = if !pc.mMediaEmulated.mRawPtr.is_null() {
             pc.mMediaEmulated.mRawPtr
         } else {
-            pc.mMedium
+            pc.mMedium as *const bindings::nsAtom as *mut _
         };
 
         MediaType(CustomIdent(unsafe { Atom::from_raw(medium_to_use) }))