Bug 1916589 - Move forced-colors computation to nsPresContext. r=nchevobbe

Untested, but something like this is what I meant above.

Differential Revision: https://phabricator.services.mozilla.com/D221773

layout/base/nsPresContext.cpp

@@ -297,7 +297,8 @@ nsPresContext::nsPresContext(dom::Document* aDocument, nsPresContextType aType)
 #ifdef DEBUG
       mInitialized(false),
 #endif
-      mOverriddenOrEmbedderColorScheme(dom::PrefersColorSchemeOverride::None) {
+      mOverriddenOrEmbedderColorScheme(dom::PrefersColorSchemeOverride::None),
+      mForcedColors(StyleForcedColors::None) {
 #ifdef DEBUG
   PodZero(&mLayoutPhaseCount);
 #endif
@@ -328,6 +329,7 @@ nsPresContext::nsPresContext(dom::Document* aDocument, nsPresContextType aType)
   }
 
   UpdateFontVisibility();
+  UpdateForcedColors(/* aNotify = */ false);
 }
 
 static const char* gExactCallbackPrefs[] = {
@@ -617,6 +619,7 @@ void nsPresContext::PreferenceChanged(const char* aPrefName) {
   if (PreferenceSheet::AffectedByPref(prefName)) {
     restyleHint |= RestyleHint::RestyleSubtree();
     PreferenceSheet::Refresh();
+    UpdateForcedColors();
   }
 
   // Same, this just frees a bunch of memory.
@@ -736,6 +739,46 @@ nsresult nsPresContext::Init(nsDeviceContext* aDeviceContext) {
   return NS_OK;
 }
 
+void nsPresContext::UpdateForcedColors(bool aNotify) {
+  auto old = mForcedColors;
+  mForcedColors = [&] {
+    if (Document()->IsBeingUsedAsImage()) {
+      return StyleForcedColors::None;
+    }
+
+    // TODO: Handle BrowsingContext override.
+
+    const auto& prefs = PrefSheetPrefs();
+    if (!prefs.mUseDocumentColors) {
+      return StyleForcedColors::Active;
+    }
+    // On Windows, having a high contrast theme also means that the OS is
+    // requesting the colors to be forced. This is mostly convenience for the
+    // front-end, which wants to reuse the forced-colors styles for chrome in
+    // this case as well, and it's a lot more convenient to use
+    // `(forced-colors)` than `(forced-colors) or ((-moz-platform: windows) and
+    // (prefers-contrast))`.
+    //
+    // TODO(emilio): We might want to factor in here the lwtheme attribute in
+    // the root element and so on.
+#ifdef XP_WINDOWS
+    if (prefs.mUseAccessibilityTheme && prefs.mIsChrome) {
+      return StyleForcedColors::Requested;
+    }
+#endif
+    return StyleForcedColors::None;
+  }();
+  if (aNotify && mForcedColors != old) {
+    MediaFeatureValuesChanged(
+        MediaFeatureChange::ForPreferredColorSchemeOrForcedColorsChange(),
+        MediaFeatureChangePropagation::JustThisDocument);
+  }
+}
+
+bool nsPresContext::ForcingColors() const {
+  return mForcedColors == StyleForcedColors::Active;
+}
+
 bool nsPresContext::UpdateFontVisibility() {
   FontVisibility oldValue = mFontVisibility;
 
@@ -924,7 +967,7 @@ void nsPresContext::SetColorSchemeOverride(
 
   if (mDocument->PreferredColorScheme() != oldScheme) {
     MediaFeatureValuesChanged(
-        MediaFeatureChange::ForPreferredColorSchemeChange(),
+        MediaFeatureChange::ForPreferredColorSchemeOrForcedColorsChange(),
         MediaFeatureChangePropagation::JustThisDocument);
   }
 }
@@ -963,6 +1006,8 @@ void nsPresContext::RecomputeBrowsingContextDependentData() {
     return browsingContext->GetEmbedderColorSchemes().mPreferred;
   }());
 
+  UpdateForcedColors();
+
   SetInRDMPane(top->GetInRDMPane());
 
   if (doc == mDocument) {
@@ -1845,6 +1890,7 @@ void nsPresContext::ThemeChangedInternal() {
   LookAndFeel::HandleGlobalThemeChange();
 
   // Full zoom might have changed as a result of the text scale factor.
+  // Forced colors might also have changed.
   RecomputeBrowsingContextDependentData();
 
   // Changes to system metrics and other look and feel values can change media
@@ -1949,7 +1995,7 @@ void nsPresContext::EmulateMedium(nsAtom* aMediaType) {
 
   MediaFeatureChange change(MediaFeatureChangeReason::MediumChange);
   if (oldScheme != mDocument->PreferredColorScheme()) {
-    change |= MediaFeatureChange::ForPreferredColorSchemeChange();
+    change |= MediaFeatureChange::ForPreferredColorSchemeOrForcedColorsChange();
   }
   MediaFeatureValuesChanged(change,
                             MediaFeatureChangePropagation::JustThisDocument);

layout/base/nsPresContext.h

@@ -85,6 +85,7 @@ class TimelineManager;
 struct MediaFeatureChange;
 enum class MediaFeatureChangePropagation : uint8_t;
 enum class ColorScheme : uint8_t;
+enum class StyleForcedColors : uint8_t;
 namespace layers {
 class ContainerLayer;
 class LayerManager;
@@ -377,10 +378,7 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
     return mozilla::PreferenceSheet::PrefsFor(*mDocument);
   }
 
-  bool ForcingColors() const {
-    return mozilla::PreferenceSheet::MayForceColors() &&
-           !PrefSheetPrefs().mUseDocumentColors;
-  }
+  bool ForcingColors() const;
 
   mozilla::ColorScheme DefaultBackgroundColorScheme() const;
   nscolor DefaultBackgroundColor() const;
@@ -560,6 +558,7 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
   void SetOverrideDPPX(float);
   void SetInRDMPane(bool aInRDMPane);
   void UpdateTopInnerSizeForRFP();
+  void UpdateForcedColors(bool aNotify = true);
 
  public:
   float GetFullZoom() { return mFullZoom; }
@@ -1402,6 +1401,7 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
   // that breaks bindgen in win32.
   FontVisibility mFontVisibility = FontVisibility::Unknown;
   mozilla::dom::PrefersColorSchemeOverride mOverriddenOrEmbedderColorScheme;
+  mozilla::StyleForcedColors mForcedColors;
 
  protected:
   virtual ~nsPresContext();

layout/style/MediaFeatureChange.h

@@ -77,7 +77,7 @@ struct MediaFeatureChange {
     return *this;
   }
 
-  static MediaFeatureChange ForPreferredColorSchemeChange() {
+  static MediaFeatureChange ForPreferredColorSchemeOrForcedColorsChange() {
     // We need to restyle because not only media queries have changed, system
     // colors may as well via the prefers-color-scheme meta tag / effective
     // color-scheme property value.

layout/style/ServoBindings.toml

@@ -595,6 +595,7 @@ cbindgen-types = [
     { gecko = "StyleImageRendering", servo = "crate::values::computed::ImageRendering" },
     { gecko = "StylePrintColorAdjust", servo = "crate::values::computed::PrintColorAdjust" },
     { gecko = "StyleForcedColorAdjust", servo = "crate::values::computed::ForcedColorAdjust" },
+    { gecko = "StyleForcedColors", servo = "crate::gecko::media_features::ForcedColors" },
     { gecko = "StyleScrollbarGutter", servo = "crate::values::computed::ScrollbarGutter" },
     { gecko = "StyleHyphenateCharacter", servo = "crate::values::computed::HyphenateCharacter" },
     { gecko = "StyleColumnCount", servo = "crate::values::computed::ColumnCount" },

servo/components/style/gecko/media_queries.rs

@@ -500,26 +500,7 @@ impl Device {
     /// Returns whether document colors are enabled.
     #[inline]
     pub fn forced_colors(&self) -> ForcedColors {
-        if self.document().mIsBeingUsedAsImage() {
-            // SVG images never force colors.
-            return ForcedColors::None;
-        }
-        let prefs = self.pref_sheet_prefs();
-        if !prefs.mUseDocumentColors {
-            return ForcedColors::Active;
-        }
-        // On Windows, having a high contrast theme also means that the OS is requesting the
-        // colors to be forced. This is mostly convenience for the front-end, which wants to
-        // reuse the forced-colors styles for chrome in this case as well, and it's a lot
-        // more convenient to use `(forced-colors)` than
-        // `(forced-colors) or ((-moz-platform: windows) and (prefers-contrast))`.
-        //
-        // TODO(emilio): We might want to factor in here the lwtheme attribute in the root element
-        // and so on.
-        if cfg!(target_os = "windows") && prefs.mUseAccessibilityTheme && prefs.mIsChrome {
-            return ForcedColors::Requested;
-        }
-        ForcedColors::None
+        self.pres_context().map_or(ForcedColors::None, |pc| pc.mForcedColors)
     }
 
     /// Computes a system color and returns it as an nscolor.

servo/ports/geckolib/cbindgen.toml

@@ -305,6 +305,7 @@ include = [
   "ImageRendering",
   "PrintColorAdjust",
   "ForcedColorAdjust",
+  "ForcedColors",
   "ScrollbarGutter",
   "ScrollDirection",
   "HyphenateCharacter",